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Author Archive

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  1. 1986: Thompson, Lonnie G., et al. “The Little Ice Age as recorded in the stratigraphy of the tropical Quelccaya ice cap.” Science234.4774 (1986): 361-364. The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event.
  2. 1990: Clark, James S. “Fire and climate change during the last 750 yr in northwestern Minnesota.” Ecological Monographs 60.2 (1990): 135-159. Charcoal stratigraphic analysis and fire scars on red pine (Pinus resinosa) trees were used to determine spatial and temporal occurrence of fire in 1 km2 of old—growth mixed conifer/hardwood forests in northwestern Minnesota. Charcoal was analyzed year by year on petrographic thin sections from annually laminated sediments of three small (≤5 ha) lakes having adjacent catchments. Dated fire scars (n = 150) from recent treefalls provided an independent record of the spatial patterns of past burns. Sedimentology of the varved sediments, water—balance models that use 150 yr of instrumental temperature and precipitation data, and published data were used to identify climate changes in separate studies, and they were used in this study to examine the possible connection between changing fire regimes and climate change. Fire—history data were used to show the changing probability of fire with time since the last fire and the effects of spatial variance (slope and aspect) on the distribution of fires through time. Over the last 750 yr, fire was most frequent (8.6 ± 2.9—yr intervals) during the warm/dry 15th and 16th centuries. Intervals were longer (13.2 ± 8.0 yr) during cooler/moister times from AD 1240 to 1440 and since 1600 (the Little Ice Age). The fire regime during the Little Ice Age consisted of periods during the mid—18th and mid—19th centuries characterized by longer fire intervals of 24.5 ± 10.4 and 43.6 ± 15.9 yr, respectively, and short—term warm/dry periods from 1770 to 1820 and 1870 to 1920 when intervals were 17.9 ± 10.6 and 12.7 ± 10.1, respectively. The probability of fire increased through time, probably in step with fuel accumulation. South— and west—facing slopes burned more frequently than did north and east aspects. Fire suppression began in 1910. During warm periods, probability of fire was sufficiently high that a continuous litter layer was all that was necessary for fire to spread and scar trees. During cool and moist times fire was most likely to occur in years with higher moisture deficits. The combined methods for fire—history analysis provided a more detailed spatial and temporal documentation of fire regimes than has previously been possible from analysis of fire scars or of charcoal counts derived from fossil pollen preparations. Results support predictions of particle—motion physics that thin sections record a local fire history. Because climate varies continuously, the responsiveness of disturbance regime to short— and long—term climatic change suggests caution in the interpretation of fire frequencies that derive from space/time analogies or extrapolation from short—term data.
  3. 1993: Bradley, Raymond S., and Philip D. Jonest. “‘Little Ice Age’summer temperature variations: their nature and relevance to recent global warming trends.” The Holocene 3.4 (1993): 367-376. Climatic changes resulting from greenhouse gases will be superimposed on natural climatic variations. High-resolution proxy records of past climate can be used to extend our perspective on regional and hemispheric changes of climate back in time by several hundred years. Using historical, tree-ring and ice core data, we examine climatic variations during the period commonly called the ‘Little Ice Age’. The coldest conditions of the last 560 years were between AD 1570 and 1730, and in the nineteenth century. Unusually warm conditions have prevailed since the 1920s, probably related to a relative absence of major explosive volcanic eruptions and higher levels of greenhouse gases.
  4. 1996: Rumsby, Barbara T., and Mark G. Macklin. “River response to the last neoglacial (the ‘Little Ice Age’) in northern, western and central Europe.” Geological Society, London, Special Publications 115.1 (1996): 217-233. Climate changes since AD 1200 have been of high magnitude. Significant lowering of temperatures occurred during the neoglacial (‘Little Ice Age’), between AD 1200–1400 and AD 1600–1800 with maximum cooling in the mid-late eighteenth century. At this time many European valley/cirque glaciers reached their maximum extent since the late Pleistocene. Neoglaciation was followed by an overall warming trend, although with significant reversals superimposed. Alongside these temperature changes were variations in the nature and amount of precipitation, and in consequence, river basins in north, west and central Europe experienced enhanced fluvial activity between 1250 and 1550 and particularly between 1750 and 1900. These phases coincide with periods of climatic transition; cooling after the Medieval optimum and warming during the latter stages of the Little Ice Age respectively. In contrast, the intervening period (1550–1750), which corresponds with the most severe phases of the last neoglacial, was associated with lower rates of fluvial activity.
  5. 1996: Keigwin, Lloyd D. “The little ice age and medieval warm period in the Sargasso Sea.” Science (1996): 1504-1508. Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbondated box core show that SST was ∼1°C cooler than today ∼400 years ago (the Little Ice Age) and 1700 years ago, and ∼1°C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation.
  6. 1998: Fischer, Hubertus, et al. “Little ice age clearly recorded in northern Greenland ice cores.” Geophysical Research Letters25.10 (1998): 1749-1752. Four ice cores drilled in the little investigated area of northern and northeastern Greenland were evaluated for their isotopic (δ18O) and chemical content. From these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced, which reveals distinct climate cooling during the 17th and the first half of the 19th century. Timing of the preindustrial temperature deviations agrees well with other northern hemisphere temperature reconstructions, however, their extent (∼1°C) significantly exceeds both continental records as well as previous southern and central Greenland ice core time series. A 20–30% increase in the sea salt aerosol load during these periods supports accompanying circulation changes over the North Atlantic. Comparison with records of potential natural climate driving forces points to an important role of the long‐term solar influence but to only episodically relevant cooling during years directly following major volcano eruptions.
  7. 1999: Lean, Judith, and David Rind. “Evaluating sun–climate relationships since the Little Ice Age.” Journal of Atmospheric and Solar-Terrestrial Physics 61.1-2 (1999): 25-36. From the coldest period of the Little Ice Age to the present time, the surface temperature of the Earth increased by perhaps 0.8°C. Solar variability may account for part of this warming which, during the past 350 years, generally tracks fluctuating solar activity levels. While increases in greenhouse gas concentrations are widely assumed to be the primary cause of recent climate change, surface temperatures nevertheless varied significantly during pre-industrial periods, under minimal levels of greenhouse gas variations. A climate forcing of 0.3 W m−2 arising from a speculated 0.13% solar irradiance increase can account for the 0.3°C surface warming evident in the paleoclimate record from 1650 to 1790, assuming that climate sensitivity is 1°C W−1 m−2 (which is within the IPCC range). The empirical Sun–climate relationship defined by these pre-industrial data suggests that solar variability may have contributed 0.25°C of the 0.6°C subsequent warming from 1900 to 1990, a scenario which time dependent GCM simulations replicate when forced with reconstructed solar irradiance. Thus, while solar variability likely played a dominant role in modulating climate during the Little Ice Age prior to 1850, its influence since 1900 has become an increasingly less significant component of climate change in the industrial epoch. It is unlikely that Sun–climate relationships can account for much of the warming since 1970, not withstanding recent attempts to deduce long term solar irradiance fluctuations from the observational data base, which has notable occurrences of instrumental drifts. Empirical evidence suggests that Sun–climate relationships exist on decadal as well as centennial time scales, but present sensitivities of the climate system are insufficient to explain these short-term relationships. Still to be simulated over the time scale of the Little Ice Age to the present is the combined effect of direct radiative forcing, indirect forcing via solar-induced ozone changes in the atmosphere, and speculated charged particle mechanisms whose pathways and sensitivities are not yet specified.
  8. 1999: Free, Melissa, and Alan Robock. “Global warming in the context of the Little Ice Age.” Journal of Geophysical Research: Atmospheres 104.D16 (1999): 19057-19070. Understanding the role of volcanic and solar variations in climate change is important not only for understanding the Little Ice Age but also for understanding and predicting the effects of anthropogenic changes in atmospheric composition in the twentieth century and beyond. To evaluate the significance of solar and volcanic effects, we use four solar reconstructions and three volcanic indices as forcings to an energy‐balance model and compare the results with temperature reconstructions. Our use of a model representing the climate system response to solar and volcanic forcings distinguishes this from previous direct comparisons of forcings with temperature series for the Little Ice Age. Use of the model allows us to assess the effects of the ocean heat capacity on the evolution of the temperature response. Using a middle‐of‐the‐road model sensitivity of 3°C for doubled CO2, solar forcings of less than 0.5% are too small to account for the cooling of the Little Ice Age. Volcanic forcings, in contrast, give climate responses comparable in amplitude to the changes of the Little Ice Age. A combination of solar and volcanic forcings explains much of the Little Ice Age climate change, but these factors alone cannot explain the warming of the twentieth century. The best simulations of the period since 1850 include anthropogenic, solar, and volcanic forcings.
  9. 1999: Bond, Gerard C., et al. “The North Atlantic’s 1‐2 kyr climate rhythm: relation to Heinrich events, Dansgaard/Oeschger cycles and the Little Ice Age.” Mechanisms of global climate change at millennial time scales 112 (1999): 35-58. New evidence from deep-sea sediment cores in the subpolar North Atlantic demonstrates that a significant component of sub-Milankovitch climate variability occurs in distinct 1-2 kyr cycles. We have traced that cyclicity from the present to within marine isotope stage 5, an interval spanning more than 80 kyrs. The most robust indicators of the cycle are repeated increases in the percentages of two petrologic tracers, Icelandic glass and hematite-stained grains. Both are sensitive measures of ice rafting episodes associated with ocean surface coolings. The petrologic tracers exhibit a consistent relation to Heinrich events, implying that mechanisms forcing Heinrich events were closely linked to those forcing the cyclicity. Our records further suggest that Dansgaard/Oeschger events may be amplifications of the cycle brought about by the impact of iceberg (fresh water) discharges on North Atlantic thermohaline circulation. The tendency of thermohaline circulation to undergo threshold behavior only when fresh water input is relatively large may explain the absence of Dansgaard/Oeschger events in the Holocene and their long pacings (thousands of years) in the early part of the glaciation. Finally, evidence from cores near Newfoundland confirms previous suggestions that the Little Ice Age was the most recent cold phase of the 1-2 kyr cycle and that the North Atlantic tended to oscillate in a muted Dansgaard/Oeschger-like mode during the Holocene.
  10. 2000: Reiter, Paul. “From Shakespeare to Defoe: malaria in England in the Little Ice Age.” Emerging infectious diseases 6.1 (2000): Present global temperatures are in a warming phase that began 200 to 300 years ago. Some climate models suggest that human activities may have exacerbated this phase by raising the atmospheric concentration of carbon dioxide and other greenhouse gases. Discussions of the potential effects of the weather include predictions that malaria will emerge from the tropics and become established in Europe and North America. The complex ecology and transmission dynamics of the disease, as well as accounts of its early history, refute such predictions. Until the second half of the 20th century, malaria was endemic and widespread in many temperate regions, with major epidemics as far north as the Arctic Circle. From 1564 to the 1730s the coldest period of the Little Ice Age malaria was an important cause of illness and death in several parts of England. Transmission began to decline only in the 19th century, when the present warming trend was well under way. The history of the disease in England underscores the role of factors other than temperature in malaria transmission.
  11. 2001: Ogilvie, Astrid EJ, and Trausti Jónsson. “” Little ice age” research: A perspective from Iceland.” Climatic Change 48.1 (2001): 9-52. The development during the nineteenth and twentieth centuries of the sciences of meteorology and climatology and their subdisciplines has made possible an ever-increasing understanding of the climate of the past. In particular, the refinement of palaeoclimatic proxy data has meant that the climate of the past thousand years has begun to be extensively studied. In the context of this research, it has often been suggested that a warm epoch occurred in much of northern Europe, the north Atlantic, and other parts of the world, from around the ninth through the fourteenth centuries, and that this was followed by a decline in temperatures culminating in a “Little Ice Age” from about 1550 to 1850 (see e.g. Lamb, 1965, 1977; Flohn, 1978). The appelations “Medieval Warm Period” and “Little Ice Age” have entered the literature and are frequently used without clear definition. More recently, however, these terms have come under closer scrutiny (see, e.g. Ogilvie, 1991, 1992; Bradley and Jones, 1992; Mikami, 1992; Briffa and Jones, 1993; Bradley and Jones, 1993; Hughes and Diaz, 1994; Jones et al., 1998; Mann et al., 1999; Crowley and Lowery, 2000). As research continues into climatic fluctuations over the last 1000 to 2000 years, a pattern is emerging which suggests a far more complex picture than early research into the history of climate suggested. In this paper, the origins of the term “Little Ice Age” are considered. Because of the emphasis on the North Atlantic in this volume, the prime focus is on research that has been undertaken in this region, with a perspective on the historiography of historical climatology in Iceland as well as on the twentieth-century climate of Iceland. The phrase “Little Ice Age” has become part of the scientific and popular thinking on the climate of the past thousand years. However, as knowledge of the climate of the Holocene continues to grow, the term now seems to cloud rather than clarify thinking on the climate of the past thousand years. It is hoped that the discussion here will encourage future researchers to focus their thinking on exactly and precisely what is meant when the term “Little Ice Age” is used.
  12. 2001: Grove, Jean M. “The initiation of the” Little Ice Age” in regions round the North Atlantic.” Climatic change 48.1 (2001): 53-82. The “Little Ice Age” was the most recent period during which glaciers extended globally, their fronts oscillating about advanced positions. It is frequently taken as having started in the sixteenth or seventeenth century and ending somewhere between 1850 and 1890, but Porter (1981) pointed out that the “Little Ice Age” may ‘have begun at least three centuries earlier in the North Atlantic region than is generally inferred’. The glacial fluctuations of the last millennium have been traced in the greatest detail in the Swiss Alps, where the “Little Ice Age” is now seen as starting with advances in the thirteenth century, and reaching an initial culmination in the fourteenth century. In the discussion here, evidence from Canada, Greenland, Iceland, Spitsbergen and Scandinavia is compared with that from Switzerland. Such comparisons have been facilitated by improved methods of calibrating radiocarbon dates to calendar dates and by increasing availability of evidence revealed during the current retreat phase. It is concluded that the “Little Ice Age” was initiated before the early fourteenth century in regions surrounding the North Atlantic.
  13. 2002: Hendy, Erica J., et al. “Abrupt decrease in tropical Pacific sea surface salinity at end of Little Ice Age.” Science 295.5559 (2002): 1511-1514. A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores from the Great Barrier Reef, Australia, indicates that sea surface temperature and salinity were higher in the 18th century than in the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific
  14. 2002: Mann, Michael E. “Little ice age.” Encyclopedia of global environmental change 1 (2002): 504-509. The term Little Ice Age is reserved for the most extensive recent period of mountain glacier expansion and is conventionally defined as the 16th–mid 19th century period during which European climate was most strongly impacted. This period begins with a trend towards enhanced glacial
    conditions in Europe following the warmer conditions of the so-called medieval warm period or medieval climatic optimum of Europe (see Medieval Climatic Optimum, Volume 1), and terminates with the dramatic retreat of these glaciers during the 20th century. While there is evidence that many other regions outside Europe exhibited periods of cooler conditions, expanded glaciation, and significantly altered climate conditions, the timing and nature of these variations are highly variable from region to region, and the notion of the Little Ice Age as a globally synchronous cold period has all but been dismissed (Bradley and Jones, 1993; Mann et al., 1999). If defined as a large-scale event, the Little Ice Age must instead be considered a time of modest cooling of the Northern Hemisphere, with temperatures dropping by about 0.6 °C during the 15th–19th
  15. 2003: Nesje, Atle, and Svein Olaf Dahl. “The ‘Little Ice Age’–only temperature?.” The Holocene 13.1 (2003): 139-145. Understanding the climate of the last few centuries, including the ‘Little Ice Age’, may help us better understand modern-day natural climate variability and make climate predictions. The conventional view of the climate development during the last millennium has been that it followed the simple sequence of a ‘Mediaeval Warm Period’, a cool ‘Little Ice Age’ followed by warming in the later part of the nineteenth century and during the twentieth century. This view was mainly based on evidence from western Europe and the North Atlantic region. Recent research has, however, challenged this rather simple sequence of climate development in the recent past. Data presented here indicate that the rapid glacier advance in the early eighteenth century in southern Norway was mainly due to increased winter precipitation: mild, wet winters due to prevailing ‘positive North Atlantic Oscillation (NAO) weather mode’ in the first half of the eighteenth century; and not only lower summer temperatures. A comparison of recent mass-balance records and ‘Little Ice Age’ glacier fluctuations in southern Norway and the European Alps suggests that the asynchronous ‘Little Ice Age’ maxima in the two regions may be attributed to multidecadal trends in the north–south dipole NAO pattern.
  16. 2005: Matthews, John A., and Keith R. Briffa. “The ‘Little Ice Age’: re‐evaluation of an evolving concept.” Geografiska Annaler: Series A, Physical Geography 87.1 (2005): 17-36. This review focuses on the development of the ‘Little Ice Age’ as a glaciological and climatic concept, and evaluates its current usefulness in the light of new data on the glacier and climatic variations of the last millennium and of the Holocene. ‘Little Ice Age’ glacierization occurred over about 650 years and can be defined most precisely in the European Alps (c. AD 1300–1950) when extended glaciers were larger than before or since. ‘Little Ice Age’ climate is defined as a shorter time interval of about 330 years (c. AD 1570–1900) when Northern Hemisphere summer temperatures (land areas north of 20°N) fell significantly below the AD 1961–1990 mean. This climatic definition overlaps the times when the Alpine glaciers attained their latest two highstands (AD 1650 and 1850). It is emphasized, however, that ‘Little Ice Age’ glacierization was highly dependent on winter precipitation and that ‘Little Ice Age’ climate was not simply a matter of summer temperatures. Both the glacier‐centred and the climate‐centred concepts necessarily encompass considerable spatial and temporal variability, which are investigated using maps of mean summer temperature variations over the Northern Hemisphere at 30‐year intervals from AD 1571 to 1900. ‘Little Ice Age’‐type events occurred earlier in the Holocene as exemplified by at least seven glacier expansion episodes that have been identified in southern Norway. Such events provide a broader context and renewed relevance for the ‘Little Ice Age’, which may be viewed as a ‘modern analogue’ for the earlier events; and the likelihood that similar events will occur in the future has implications for climatic change in the twenty‐first century. It is concluded that the concept of a ‘Little Ice Age’ will remain useful only by (1) continuing to incorporate the temporal and spatial complexities of glacier and climatic variations as they become better known, and (2) by reflecting improved understanding of the Earth‐atmosphere‐ocean system and its forcing factors through the interaction of palaeoclimatic reconstruction with climate modelling.
  17. 2005: Brázdil, Rudolf, et al. “Historical climatology in Europe–the state of the art.” Climatic change 70.3 (2005): 363-430. This paper discusses the state of European research in historical climatology. This field of science and an overview of its development are described in detail. Special attention is given to the documentary evidence used for data sources, including its drawbacks and advantages. Further, methods and significant results of historical-climatological research, mainly achieved since 1990, are presented. The main focus concentrates on data, methods, definitions of the “Medieval Warm Period” and the “Little Ice Age”, synoptic interpretation of past climates, climatic anomalies and natural disasters, and the vulnerability of economies and societies to climate as well as images and social representations of past weather and climate. The potential of historical climatology for climate modelling research is discussed briefly. Research perspectives in historical climatology are formulated with reference to data, methods, interdisciplinarity and impacts.
  18. 2006: Pfister, Christian, and Rudolf Brázdil. “Social vulnerability to climate in the” Little Ice Age“: an example from Central Europe in the early 1770s.” Climate of the Past 2.2 (2006): 115-129. The paper is oriented on social vulnerability to climate in Switzerland and in the Czech Lands during the early 1770s. Documentary sources of climate related to man-made archives are discussed. Methods of temperature and precipitation reconstruction based on this evidence as well as climate impact analyses are presented. Modelling of Little Ice Age-type Impacts (LIATIMP) is applied to highlight climate impacts during the period 1750?1800 in the Swiss Plateau and in the Czech Lands. LIATIMP are defined as adverse climate situations affecting agricultural production, mainly in terms of rainy autumns, cold springs and rainy harvest-periods. The most adverse weather patterns according to this model occurred from 1769 to 1771 causing two, in the case of the Czech Lands even three successive harvest failures. The paper addresses the social and economic consequences of this accumulation of climatic stress and explores how the authorities and the victims dealt with this situation.
  19. 2008: Crowley, Thomas J., et al. “Volcanism and the little ice age.” PAGES news 16.2 (2008): 22-23.  Although solar variability has often been considered the primary agent for LIA cooling, the most comprehensive test of this explanation (Hegerl et al., 2003) points instead to volcanism being substantially more important, explaining as much as 40% of the decadal-scale variance during the LIA. Yet, one problem that has continually plagued climate researchers is that the paleovolcanic record, reconstructed from Antarctic and Greenland ice cores, cannot be well calibrated against the instrumental record. This is because the primary in-strumental volcano reconstruction used by the climate community is that of Sato et al. (1993), which is relatively poorly con-strained by observations prior to 1960 (es-pecially in the southern hemisphere). Here, we report on a new study that has successfully calibrated the Antarctic sulfate record of volcanism from the 1991 eruptions of Pinatubo (Philippines) and Hudson (Chile) against satellite aerosol op-tical depth (AOD) data (AOD is a measure of stratospheric transparency to incoming solar radiation). A total of 22 cores yield an area-weighted sulfate accumulation rate of 10.5 kg/km2, which translates into a conversion rate for AOD of 0.011 AOD/kg/km2 sulfate. We validated our time series by comparing a canonical growth and decay curve for eruptions for Krakatau (1883), the 1902 Caribbean eruptions (pri marily Santa Maria), and the 1912 eruption of Novarupta/Katmai (Alaska) against a reanalysis (Stothers, 1996) of the original AOD data and lunar eclipse estimates of AOD for Krakatau (Keen, 1983). The agreement (Fig. 1) is very good—essentially within the uncertainty of the independent data. Our new ice core reconstruction shows several significant disagreements with the Sato et al. (1993).
  20. 2009: Mann & Zhang. “Global signatures and dynamical origins of the Little Ice Age and Medieval Climate Anomaly.” Science 326.5957 (2009): 1256-1260. Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña–like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation–Arctic Oscillation.
  21. 2011: Bertler, N. A. N., P. A. Mayewski, and L. Carter. “Cold conditions in Antarctica during the Little Ice Age—Implications for abrupt climate change mechanisms.” Earth and Planetary Science Letters 308.1 (2011): 41-51. The Little Ice Age (LIA) is one of the most prominent climate shifts in the past 5000 yrs. It has been suggested that the LIA might be the most recent of the Dansgaard–Oeschger events, which are better known as abrupt, large scale climate oscillations during the last glacial period. If the case, then according to Broecker (2000a, 2000b) Antarctica should have warmed during the LIA, when the Northern Hemisphere was cold. Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~ 2 °C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. Whilst we find there was large spatial and temporal variability, overall Antarctica was cooler and stormier during the LIA. Although temperatures have warmed since the termination of the LIA, atmospheric circulation strength has remained at the same, elevated level. We conclude, that the LIA was either caused by alternative forcings, or that the sea-saw mechanism operates differently during warm periods.
  22. 2012: Orsi, Anais J., Bruce D. Cornuelle, and Jeffrey P. Severinghaus. “Little Ice Age cold interval in West Antarctica: evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) divide.” Geophysical Research Letters 39.9 (2012).  The largest climate anomaly of the last 1000 years in the Northern Hemisphere was the Little Ice Age (LIA) from 1400–1850 C.E., but little is known about the signature of this event in the Southern Hemisphere, especially in Antarctica. We present temperature data from a 300 m borehole at the West Antarctic Ice Sheet (WAIS) Divide. Results show that WAIS Divide was colder than the last 1000‐year average from 1300 to 1800 C.E. The temperature in the time period 1400–1800 C.E. was on average 0.52 ± 0.28°C colder than the last 100‐year average. This amplitude is about half of that seen at Greenland Summit (GRIP). This result is consistent with the idea that the LIA was a global event, probably caused by a change in solar and volcanic forcing, and was not simply a seesaw‐type redistribution of heat between the hemispheres as would be predicted by some ocean‐circulation hypotheses. The difference in the magnitude of the LIA between Greenland and West Antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions
  23. 2012: Miller, Gifford H., et al. “Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea‐ice/ocean feedbacks.” Geophysical Research Letters 39.2 (2012). Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes. However, the causes of superposed century‐scale cold summer anomalies, of which the Little Ice Age (LIA) is the most extreme, remain debated, largely because the natural forcings are either weak or, in the case of volcanism, short lived. Here we present precisely dated records of ice‐cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea‐ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50‐year‐long episode with four large sulfur‐rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea‐ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required.
  24. 2013: Lehner, Flavio, et al. “Amplified inception of European Little Ice Age by sea ice–ocean–atmosphere feedbacks.” Journal of Climate 26.19 (2013): 7586-7602. The inception of the Little Ice Age (~1400–1700 AD) is believed to have been driven by an interplay of external forcing and climate system internal variability. While the hemispheric signal seems to have been dominated by solar irradiance and volcanic eruptions, the understanding of mechanisms shaping the climate on a continental scale is less robust. In an ensemble of transient model simulations and a new type of sensitivity experiments with artificial sea ice growth, the authors identify a sea ice–ocean–atmosphere feedback mechanism that amplifies the Little Ice Age cooling in the North Atlantic–European region and produces the temperature pattern suggested by paleoclimatic reconstructions. Initiated by increasing negative forcing, the Arctic sea ice substantially expands at the beginning of the Little Ice Age. The excess of sea ice is exported to the subpolar North Atlantic, where it melts, thereby weakening convection of the ocean. Consequently, northward ocean heat transport is reduced, reinforcing the expansion of the sea ice and the cooling of the Northern Hemisphere. In the Nordic Seas, sea surface height anomalies cause the oceanic recirculation to strengthen at the expense of the warm Barents Sea inflow, thereby further reinforcing sea ice growth. The absent ocean–atmosphere heat flux in the Barents Sea results in an amplified cooling over Northern Europe. The positive nature of this feedback mechanism enables sea ice to remain in an expanded state for decades up to a century, favoring sustained cold periods over Europe such as the Little Ice Age. Support for the feedback mechanism comes from recent proxy reconstructions around the Nordic Seas.
  25. 2013: Schleussner, Carl-Friedrich, and G. Feulner. “A volcanically triggered regime shift in the subpolar North Atlantic Ocean as a possible origin of the Little Ice Age.” Climate of the Past 9.3 (2013). Among the climatological events of the last millennium, the Northern Hemisphere Medieval Climate
    Anomaly succeeded by the Little Ice Age are of exceptional importance. The origin of these regional climate anomalies remains a subject of debate and besides external influences like solar and volcanic activity, internal dynamics of the climate system might have also played a dominant role. Here, we present transient last millennium simulations of the fully coupled model of intermediate complexity Climber 3α forced with stochastically reconstructed wind-stress fields. Our results indicate that short-lived volcanic eruptions might have triggered a cascade of sea ice–ocean feedbacks in the North Atlantic, ultimately leading to a persistent regime shift in the ocean circulation. We find that an increase in the Nordic Sea sea-ice extent on decadal timescales as a consequence of major volcanic eruptions in our model leads to a spin-up of the subpolar gyre and a weakened Atlantic meridional overturning circulation, eventually causing a persistent, basin-wide cooling. These results highlight the importance of regional climate feedbacks such as a regime shift in the subpolar gyre circulation for understanding the dynamics of past and future climate.
  26. 2014: Lorrey, Andrew, et al. “The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach.” Climate dynamics 42.11-12 (2014): 3039-3060. Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of −0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. Reconstructed geopotential height at 1,000 hPa (z1000) suggests enhanced southwesterly flow across New Zealand occurred during the LIA to generate the terrestrial temperature anomalies. The mean atmospheric circulation pattern for summer resulted from a crucial reduction of the ‘HSE’-blocking synoptic type (highs over and to the west of NZ; largely settled conditions) and increases in both the ‘T’- and ‘SW’-trough synoptic types (lows passing over NZ; enhanced southerly and southwesterly flow) relative to normal. Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Niño-Modoki in the tropical Pacific and negative Southern Annular Mode activity.

noctilucent

  1. 1962: Witt, Georg. “Height, structure and displacements of noctilucent clouds.” Tellus 14.1 (1962): 1-18.Observations of noctilucent clouds have been carried out during the summer of 1958 at Torsta (63.3° N; 14.6° E) in Central Sweden. Simultaneous pairs of cloud photographs have been taken with accurate phototheodolite cameras from the end-points of a geodetically determined base-line of length 51.5 km. The picture pairs were subsequently analyzed in stereo instruments (autographs) by which Cartesian space coordinates were obtained for various points in the cloud system. These coordinates, duly corrected for atmospheric refraction, were used for determination of the height of the individual features. Through the stereoscopic effect, measurements could be made on diffuse parts of the cloud system as well as on marked details. Additional information about movements of the cloud system was obtained from a time-lapse film in Kodachrome. The results were plotted and analyzed by conventional methods and maps of the cloud topography at consecutive time intervals could be prepared. In addition to these maps, vertical cross-sections through the cloud system were made as well as detailed studies of particularly interesting cloud features. This paper gives a presentation and interpretation of the results obtained so far and a brief description of the photogrammetric technique applied. The results presented below were obtained during a very bright cloud display with good visibility conditions on August 10–11th, 1958. Thirty pairs of pictures were taken of various parts of the cloud system, which covered the entire northern horizon. Eight of these have been analyzed so far. The results can be summarized as follows. The cloud system moved in a direction north-east to south-west with velocities of the order of 50 to 100 m/s. It consisted of a continuous diffuse layer interchanging with regions of sharply defined features such as systems of parallel billows and bands, blobs and other smaller-scale irregularities of various shapes. The measured heights varied between 81.5 and 85.5 km. The long parallel bands were identified as a system of waves with wavelengths of the order of 50 km and amplitudes up to 4 km which propagated in a direction nearly opposite to that of the cloud system with absolute velocities of the order of 10 to 20 m/s. The wave crests were oriented nearly perpendicular to the main air flow and were continuous over distances of hundreds of kilometers and exhibited local refraction effects. The smaller billows had wavelengths of the order of 5–10 km and amplitudes about 0.5–1.0 km; they moved with the cloud system. The billows showed no preferred orientation and were observed to pass through the crests of the longer waves. It is indicated by the analysis the regular changes in the brightness of these clouds are due to changes of the optical thickness of the cloud layer.
  2. 1964: Hemenway, C. L., R. K. Soberman, and G. Witt. “Sampling of noctilucent cloud particles.” Tellus 16.1 (1964): 84-88. Sampling of noctilucent cloud particles by means of sounding rockets has been successfully carried out from northern Sweden in the Summer of 1962. Two successful flights were achieved, one in the presence of noctilucent clouds and one when no such clouds could be visually observed from the ground or from aircraft. The collecting surfaces were exposed between the altitudes of approximately 75 and 98 kilometers during ascent only. The particle concentration in a vertical column through the noctilucent cloud display is found to be greater than 8 × 1010particles per square meter which is at least one thousand times greater than in the case when no clouds were observed. The integral size distribution of the cloud particles is of the form N = Ad−p where 3 < p < 4. A significant fraction of the collected cloud particles had a volatile coating prior to collection. The particles were analyzed by electron diffraction, neutron activation, and electron beam microprobe techniques. Electron-beam microprobe analysis has given evidence for iron particles with high nickel content. Calcium films were used as indicators of moisture associated with the collected particles. Study of the exposed and unexposed films flown in the sampling experiments has revealed evidence for moisture. Laboratory simulation of a ring- or halo-patterns found in the electron microscopic examination of the noctilucent cloud particles has been attempted. This was done by impacting ice-coated nickel particles on collecting surfaces similar to those used in the sampling experiment. Ring patterns similar to those observed on the rocket sampling surfaces have been produced. The primary conclusions are that the cloud particles are probably of extraterrestrial origin and that a significant fraction appears to have been coated with terrestrial ice. Plans for future experiments are briefly outlined
  3. 1966: Fogle, Benson, and B. Haurwitz. “Noctilucent clouds (NLC).” Space Science Reviews 6.3 (1966): 279-340. There has been an intensive study of NLC since the I.G.Y. showed that these clouds occur over North America as frequently as they do in Europe and the U.S.S.R. NLC displays are persistent and last for periods up to and greater than 5 hours, but individual parts (particularly the billow structure) often form and decay within a few minutes or tens of minutes. The rapid structural changes in the clouds indicate that the layer in which they are formed is well stirred and often in wave motion. In the Northern Hemisphere NLC are observed predominantly between June 1 and August 15, with the peak of activity occurring around 20 to 30 days after the summer solstice and the brightest and most widespread displays taking place between July 1 and August 15. The optimum latitude for NLC observations is around 60° N. NLC occur far more frequently than previously supposed — during the month of July, NLC are seen nearly every night in some part of the Northern Hemisphere. An observer at 60° N might expect to see NLC on about 75% of the clear nights during the month of July. Occasionally NLC displays extend over an area in excess of millions of square kilometers.

    Recent studies of NLC in the Southern Hemisphere have resulted in the proof of the existence of NLC there and in the determination of some of their characteristics. Southern Hemisphere NLC were found to have a general drift motion toward the west-north-west. NLC were observed there (at 53° S) during the period December 25–January 20, with the brightest and most widespread displays occurring during the first four days of January. A comparison of these results for 53° S with those obtained from stations at 53° N suggests that NLC in the Southern Hemisphere have the same apparent frequency of occurrence with respect to the solstice as NLC in the Northern Hemisphere and that the clouds are likely to be seen at 60° S from December 1 to February 15. Geometrical considerations of NLC observations and observational results show that the clouds are likely to be seen only during the time periods when the solar depression angle (SDA) is between 6° and 16° and that they are most easily detected at SDA from 9° to 14°. At SDA greater than 16°, the 82 km level where the NLC are formed is no longer illuminated by the sun even at the observer’s horizon. An atmospheric screening height of around 30 km appears to be operative in the case of NLC. The collection and statistical analysis of all available data on NLC provides the following picture of their characteristics in the Northern Hemisphere: Color: bluish white Height: (average) 82.7 km Latitude of Observations: 45° to 80°, best at about 60° Season for Observations: March through October, best in June through August Times for Observations: nautical and part of astronomical twilight, SDA = 6° to 16° Spatial Extent: 10 000 to more than 4000 000 km2Duration: several minutes to more than 5 hours Average Velocity: 40 m/sec towards SW; individual bands often move in different directions and at different speeds than the display as a whole Thickness: 0.5 to 2 km Vertical Wave Amplitude: 1.5 to 3 km Average Particle Diameter: about 0.3 microns Number Density of Particles: 10−2 to 1 per cm3 Temperature in Presence of NLC: about 135° K. The available evidence suggests that the dust particles in NLC are of extraterrestrial origin and that they have a volatile coating, the nature of which is uncertain at this time although it is largely assumed to be water substance. The fact that no uncoated particles with diameters greater than 0.20 micron were found in the NLC samples obtained over Sweden in 1962 indicates that particles of this size are absent in the regions above and below the cloud layer. This result suggests that the larger particles may be formed in the NLC layer by coagulation of the smaller ones and that these particles are retained in the NLC layer by some mechanism such as large-scale vertical motions. Calculations of the fall speed of NLC particles indicate that the particles are likely to be of low density (below 1 g/cm3) and/or non-spherical in shape. In view of the large uncertainties remaining as to the nature of NLC particles and the characteristics of the region in which they form, a definitive theory explaining their formation must await further experimental data. A knowledge of the wind and temperature distribution would permit a decision as to whether the observed wave forms are internal gravity waves or interface waves. A knowledge of the temperature and water vapor content during the presence and absence of NLC would also be helpful in the investigation of condensation processes on NLC particles and the changes of NLC appearance. Polarization measurements at scattering angles greater than 90° would assist in determining whether NLC become visible because of an increased concentration of particles at the mesopause or because of an increase in particle size due to coating. Better information about the nature of the particles would help in making more definite theoretical deductions from ground-based optical measurements and more reliable theoretical estimates about the sinking velocities important for the theory of NLC formation. A measurement of the height of the turbopause and the turbulent state of the atmosphere in the region in question, by means of artificial vapor trails, could make an important contribution to the Chapman-Kendall theory which postulates a descent of the turbopause to the NLC region. Because of the sometimes observed disappearance of NLC when auroral displays occur, a particularly interesting experiment would be a sequence of temperature measurements in the NLC region when aurora and NLC occur together in order to see whether a warming of the region due to auroral heating can, in fact, be discovered and whether such a warming leads to significant changes or even disappearance of the NLC by removing the coating from the nuclei or by greater turbulence which would reduce the particle concentration. NLC are, even in the latitudes and seasons when they occur, relatively rare phenomena, but their study is related to many other problems connected with the mesopause, the lowest layer of the ionosphere, the lowest fringe of the auroral layer, and with the influx of cosmic dust. Thus their continued exploration can contribute greatly to our knowledge, not only of this particular level, but of our whole atmospheric and space environment.

  4. 1972: Donahue, Thomas Michael, B. Guenther, and J. E. Blamont. “Noctilucent clouds in daytime: Circumpolar particulate layers near the summer mesopause.” Journal of the Atmospheric Sciences 29.6 (1972): 1205-1209. Observations with a horizon scanning airglow photometer on OGO-6 have revealed the presence of a dense scattering layer near 80 km over the geographic pole during the local summer. The layer is detected on all satellite passes above 80° latitude beginning 15 days before the solstice. The optical depth of the layer increases by more than a factor of 50 between 70° and 85°. It is suggested that noctilucent clouds are weak sporadic manifestations of these persistent polar layers.
  5. 1982: Turco, R. P., et al. “Noctilucent clouds: Simulation studies of their genesis, properties and global influences.” Planetary and Space Science 30.11 (1982): 1147-1181. Extremely cold mesopause temperatures (<140K) are necessary to form noctilucent clouds; such temperatures only exist at high latitudes in summer. A water vapor concentration of 4–5 ppmv is sufficient to form a visible cloud. However, a subvisible cloud can exist in the presence of only 1 ppmv of H2O. Ample cloud condensation nuclei are always present in the mesosphere; at very low temperatures, either meteoric dust or hydrated ions can act as cloud nuclei. To be effective, meteoric dust particles must be larger than 10–15 Å in radius. When dust is present, water vapor supersaturations may be held to such low values that ion nucleation is not possible. Ion nucleation can occur, however, in the absence of dust or at extremely low temperatures (<130K). While dust nucleation leads to a small number (<10cm−3) of large ice particles (>0.05 μm radius) and cloud optical depths (at 550 nm) ∼10−4, ion nucleation generally leads to a large number (∼103cm−3) of smaller particles and optical depths ∼10−5). However, because calculated nucleation rates in noctilucent clouds are highly uncertain, the predominant nucleus for the clouds (i.e., dust or ions) cannot be unambiguously established. Noctilucent clouds require several hours-up to a day-to materialize. Once formed, they may persist for several days, depending on local meteorological conditions. However, the clouds can disappear suddenly if the air warms by 10–20 K. The environmental conditions which exist at the high-latitude summer mesopause, together with the microphysics of small ice crystals, dictate that particle sizes will be ≲ 0.1 μm radius. The ice crystals are probably cubic in structure. It is demonstrated that particles of this size and shape can explain the manifestations of noctilucent clouds. Denser clouds are favored by higher water vapor concentrations, more rapid vertical diffusion and persistent upward convection (which can occur at the summer pole). Noctilucent clouds may also condense in the cold “troughs” of gravity wave trains. Such clouds are bright when the particles remain in the troughs for several hours or more; otherwise they are weak or subvisible. Ambient noctilucent clouds are found to have a negligible influence on the climate of Earth. Anthropogenic perturbations of the clouds that are forecast for the next few decades are also shown to have insignificant climatology implications
  6. 1989: Gadsden, Michael, and Wilfried Schröder. “Noctilucent clouds.” Springer, Berlin, Heidelberg, 1989. 1-12. Noctilucent clouds are immediately recognizable, even when being seen for the first time. The name suggests it all: they are night-shining clouds. From mid-latitudes(ø > 50°), they can be seen during the summer in the twilight arch which moves around the north (or south, in the southern hemisphere) horizon as the night progresses. In form much like cirrostratus clouds, they are usually silvery-white or pale blue in colour and they stand out clearly behind the darker twilight sky. Ordinary (i.e. tropospheric) clouds are dark silhouettes under these conditions; noctilucent clouds shine. The reason for this is that noctilucent clouds are very high in the atmosphere and remain in sunlight long after the Sun has set at ground level.
  7. 1989: Garcia, Rolando R. “Dynamics, radiation, and photochemistry in the mesosphere: Implications for the formation of noctilucent clouds.” Journal of Geophysical Research: Atmospheres 94.D12 (1989): 14605-14615. The nature of noctilucent clouds, which occur at very great heights and high latitudes during summer, has remained something of a mystery for over 100 years. The realization that the summer mesopause is the coldest region of the Earth’s atmosphere, together with the possibility that transport by atmospheric motions could maintain a substantial mixing ratio of water vapor against very rapid chemical destruction, has led to the present consensus that noctilucent clouds are formed of water ice. A number of recently developed microphysical models have been successful in simulating cloud particle distributions whose characteristics are consistent with satellite radiance observations. However, because of the scarcity of data on temperature, dynamics, and water vapor abundances, these models have had to rely on a number of assumptions about the behavior of these quantities. This paper attempts to illustrate by means of model calculations how various dynamical and photochemical processes interact to produce the unique environment that makes possible the existence of noctilucent clouds. In particular, it focuses on how thermal relaxation influences the altitude and strength of gravity wave breaking and on the effects of such wave breaking on the circulation, temperature distribution, and transport of water vapor near the summer mesopause. It is also shown that, if present understanding of hydrogen chemistry in the mesosphere is even approximately correct, variations in Lyman α radiation should have a significant effect on water vapor abundances near the summer mesopause and, therefore, on the occurrence of noctilucent clouds.
  8. 1990: Gadsden, M. “A secular change in noctilucent cloud occurrence.” Journal of Atmospheric and Terrestrial Physics52.4 (1990): 247-251. Evidence is given for a secular change now taking place in the frequency of occurrence of noctilucent clouds. Separate lines of argument lead to the strong supposition that this change occurs as the result of a small, systematic cooling of the upper mésosphère in summertime. The change is likely to have amounted to 7 K over the last 20–30 years. While changes in water vapour concentration will affect the frequency of occurrence, it is just as likely that the changes may be taking place in the mean mesopause temperature. These changes in mean temperature increase the probability of occurrence of a low (threshold) temperature which allows cloud formation.
  9. 1993: Fritts, David C., et al. “Wave breaking signatures in noctilucent clouds.” Geophysical Research Letters 20.19 (1993): 2039-2042. Results of a recent modeling study of gravity wave breaking in three dimensions byAndreassen et al. and Fritts et al. showed wave saturation to occur via a three‐dimensional instability oriented normal to the direction of wave propagation. The instability was found to occur at horizontal scales comparable to the depth of unstable regions within the wave field and to lead to substantial vertical displacements and tilting of isentropic surfaces. Because of strong similarities between the wave and instability structures in the simulation and the structure observed in noctilucent cloud layers near the summer mesopause, we have used these model results to compute the advective effects on cloud visibility and structure for a range of viewing angles and cloud layer widths. Our results show the gravity wave breaking signature to provide a plausible explanation of the observed structures and suggest that noctilucent cloud structures may be used in turn to infer qualitative properties of gravity wave scales, energy and momentum transports, and turbulence scales near the summer mesopause.
  10. 1996: Thomas, G. E. “Is the polar mesosphere the miner’s canary of global change?.” Advances in Space Research 18.3 (1996): 149-158. The polar mesosphere is an atmospheric region located between latitude 50° and the pole, and between 50 and 90 km. During summer it becomes the coldest region on earth (<130K). This review focuses on past and future alterations of the temperature and water vapor content of this extremely cold region. These two influences are crucial for the formation of mesospheric ice particles in noctilucent clouds (NLC). A recent two-dimensional model study has been conducted of how long-term changes in carbon dioxide (CO2) and methane (CH4) concentrations may modify the temperature and water vapor concentration at mesopause heights. The model is a version of the well-known Garcia-Solomon model, modified to include accurate non-LTE cooling in the CO2 15 μm band. The existence region of NLC is defined as a domain where water-ice is supersaturated. Reduced levels of CO2 and CH4 are found to confine the model NLC existence region to within the perpetually-sunlit polar cap region, where the clouds would no longer be visible to a ground observer. A doubling of CO2 and CH4 could extend the NLC region to mid-latitudes, where they would be observable by a large fraction of the world’s population.
  11. 1997: Cho, John YN, and Jürgen Röttger. “An updated review of polar mesosphere summer echoes: Observation, theory, and their relationship to noctilucent clouds and subvisible aerosols.” Journal of Geophysical Research: Atmospheres102.D2 (1997): 2001-2020. Peculiar atmospheric radar echoes from the high‐latitude summer mesosphere have spurred much research in recent years. The radar data (taken on frequency bands ranging from 2 to 1290 MHz) have been supplemented by measurements from an increasing arsenal of in situ (rocket borne) and remote sensing (satellites and lidars) instruments. Theories to explain these polar mesosphere summer echoes (PMSEs) have also proliferated. Although each theory is distinct and fundamentally different, they all share the feature of being dependent on the existence of electrically charged aerosols. It is therefore natural to assume that PMSEs are intimately linked to the other fascinating phenomenon of the cold summer mesopause, noctilucent clouds (NLCs), which are simply ice aerosols that are large enough to be seen by the naked eye. In this paper we critically examine both the data collected and the theories proposed, with a special focus on the relationship between PMSEs and NLCs.
  12. 2001: Rosenlof, K. H., et al. “Stratospheric water vapor increases over the past half‐century.” Geophysical research letters 28.7 (2001): 1195-1198. Ten data sets covering the period 1954–2000 are analyzed to show a 1%/yr increase in stratospheric water vapor. The trend has persisted for at least 45 years, hence is unlikely the result of a single event, but rather indicative of long‐term climate change. A long‐term change in the transport of water vapor into the stratosphere is the most probable cause.
  13. 2002: Wickwar, Vincent B., et al. “Visual and lidar observations of noctilucent clouds above Logan, Utah, at 41.7 N.” Journal of Geophysical Research: Atmospheres 107.D7 (2002). Noctilucent clouds (NLCs) were observed from a midlatitude site (Logan, Utah) on the evenings of 22 and 23 June 1999 mountain daylight time. On both nights the clouds were seen for approximately an hour by experienced observers, and they were photographed. The NLC was also observed on the second evening for approximately an hour in the zenith with the Rayleigh‐scatter lidar at the Atmospheric Lidar Observatory, which is operated by the Center for Atmospheric and Space Sciences on the campus of Utah State University. These observations enabled several of the properties of the cloud to be determined. They were within the range of those observed at higher latitudes, but notably the NLC was very weak and thin. These combined visual and lidar observations unequivocally support the identification of the cloud as a noctilucent cloud. The midlatitude location (41.74°N, 111.81°W) is ∼10° equatorward of previous observations. This equatorward penetration is significant because of potential implications about global change or the global circulation.
  14. 2003: Zahn, Ulf. “Are noctilucent clouds a “Miner’s Canary” for global change?.” EOS, Transactions American Geophysical Union84.28 (2003): 261-264. Noctilucent clouds (NLC) occur close to 83 km altitude during summer at polar, high, and mid‐latitudes. They are frequently visible to Earth‐bound observers, provided the observers are on the night side of Earth and the clouds are still illuminated by the Sun. Under these conditions, NLC can become a quite impressive sight. NLC owe their existence to the extremely low temperatures (well below 150 K) which prevail during summer over a wide latitude band in the 82‐ to 90‐km altitude region. For a major review of NLC science, the reader is referred to Gadsden and Schröder [1989].
  15. 2007: Karlsson, Bodil, Heiner Körnich, and Jörg Gumbel. “Evidence for interhemispheric stratosphere‐mesosphere coupling derived from noctilucent cloud properties.” Geophysical Research Letters 34.16 (2007). We investigate the link between the cold summer mesopause region and the dynamics in the stratosphere. In particular, we use Odin observations of noctilucent cloud (NLC) properties as a proxy for the state of the summer mesosphere and ECMWF winter stratospheric temperatures as a proxy for the residual circulation in the stratosphere. Large areas of strong anticorrelation between winter stratospheric temperature and summer mesospheric NLC indicate that there is an interhemispheric connection. Time‐lagged cross correlation shows that the wave activity flux at 100 hPa leads the NLC response by several weeks. The presented findings are consistent with recent model studies where the modulation of the mesospheric gravity wave drag by the stratospheric planetary waves yields an interhemispheric stratosphere‐mesosphere coupling.
  16. 2017: Kuilman, Maartje, et al. “Exploring noctilucent cloud variability using the nudged and extended version of the Canadian Middle Atmosphere Model.” Journal of Atmospheric and Solar-Terrestrial Physics 164 (2017): 276-288. Ice particles in the summer mesosphere – such as those connected to noctilucent clouds and polar mesospheric summer echoes – have since their discovery contributed to the uncovering of atmospheric processes on various scales ranging from interactions on molecular levels to global scale circulation patterns. While there are numerous model studies on mesospheric ice microphysics and how the clouds relate to the background atmosphere, there are at this point few studies using comprehensive global climate models to investigate observed variability and climatology of noctilucent clouds. In this study it is explored to what extent the large-scale inter-annual characteristics of noctilucent clouds are captured in a 30-year run – extending from 1979 to 2009 – of the nudged and extended version of the Canadian Middle Atmosphere Model (CMAM30). To construct and investigate zonal mean inter-seasonal variability in noctilucent cloud occurrence frequency and ice mass density in both hemispheres, a simple cloud model is applied in which it is assumed that the ice content is solely controlled by the local temperature and water vapor volume mixing ratio. The model results are compared to satellite observations, each having an instrument-specific sensitivity when it comes to detecting noctilucent clouds. It is found that the model is able to capture the onset dates of the NLC seasons in both hemispheres as well as the hemispheric differences in NLCs, such as weaker NLCs in the SH than in the NH and differences in cloud height. We conclude that the observed cloud climatology and zonal mean variability are well captured by the model.
  17. 2017: Fiedler, Jens, et al. “Long-term variations of noctilucent clouds at ALOMAR.” Journal of Atmospheric and Solar-Terrestrial Physics 162 (2017): 79-89. Noctilucent clouds (NLC) are measured by the Rayleigh/Mie/Raman-lidar at the ALOMAR research facility in Northern Norway (69°N, 16°E) since 1994. The data set contains about 2860 h of NLC detections and is investigated for the first time regarding trends. NLC properties depend on cloud brightness which is taken into account by the use of several cloud classes, related to brightness ranges. For NLC brighter than the long-term detection limit and strong NLC, respectively, the trend terms show increasing occurrence frequency (+9%/dec and+5%/dec) and brightness (+1.7×10−10 m−1 sr−1/dec and +1.5×−10 m−1sr−1/dec) from 1998 to 2015. In the same period the altitude of faint and long-term limit clouds decreases (−66 m/dec and −108 m/dec). Over the entire time period of 22 years strong clouds show an increasing altitude by +76 m/dec. NLC properties are affected differently by solar and atmospheric parameters. In general, Lyman-α and stratospheric ozone impact all three NLC parameters, temperature at 83 km impacts mainly the NLC altitude. Time series of RMR lidarand SBUV satellite instruments match best for NLC occurrence frequency and brightness when restricting SBUV to the morning data at longitudes around ALOMAR (64–74°N, 8–24°E/0–9 LT). This suggests longitudinal dependent trends, which is confirmed by trend investigations of longitudinal subsets of the SBUV data set.
    • 2017: Von Savigny, Christian, Matthew T. DeLand, and Michael J. Schwartz. “First identification of lunar tides in satellite observations of noctilucent clouds.” Journal of Atmospheric and Solar-Terrestrial Physics 162 (2017): 116-121. Noctilucent clouds (NLCs) are optically thin ice clouds occurring near the polar summer mesopause. NLCs are a highly variable phenomenon subject to different sources of variability. Here we report on a poorly understood mechanism affecting NLCs, i.e., the lunar gravitational tide. We extract remarkably clear and statistically highly significant lunar semidiurnal tidal signatures in NLC occurrence frequency, NLC albedo and NLC ice water content from observations with the Solar Backscatter Ultraviolet (SBUV) satellite instruments using the superposed epoch analysis method applied to a data set covering more than 3 decades. The lunar semidiurnal tide is identified in NLC measurements in both hemispheres. In addition, lunar semidiurnal tidal signatures in polar summer mesopause temperature were extracted from space borne observations with the Microwave Limb Sounder (MLS) and the phases of the lunar tidal signatures in NLC parameters and temperature are demonstrated to be consistent. To our best knowledge these results constitute the first identification of the lunar tide in non-visual NLC observations.
    • 2017: Ugolnikov, Oleg S., et al. “Noctilucent cloud particle size determination based on multi-wavelength all-sky analysis.” Planetary and Space Science 146 (2017): 10-19. The article deals with the analysis of color distribution in noctilucent clouds (NLC) in the sky based on multi-wavelength (RGB) CCD-photometry provided with the all-sky camera in Lovozero in the north of Russia (68.0°N, 35.1°E) during the bright expanded NLC performance in the night of August 12, 2016. Small changes in the NLC color across the sky are interpreted as the atmospheric absorption and extinction effects combined with the difference in the Mie scattering functions of NLC particles for the three color channels of the camera. The method described in this paper is used to find the effective monodisperse radius of particles about 55 nm. The result of these simple and cost-effective measurements is in good agreement with previous estimations of comparable accuracy. Non-spherical particles, Gaussian and lognormal distribution of the particle size are also considered
    • 2018: Köhnke, Merlin C., Christian von Savigny, and Charles E. Robert. “Observation of a 27-day solar signature in noctilucent cloud altitude.” Advances in Space Research 61.10 (2018): 2531-2539. Previous studies have identified solar 27-day signatures in several parameters in the Mesosphere/Lower thermosphere region, including temperature and Noctilucent cloud (NLC) occurrence frequency. In this study we report on a solar 27-day signature in NLC altitude with peak-to-peak variations of about 400 m. We use SCIAMACHY limb-scatter observations from 2002 to 2012 to detect NLCs. The superposed epoch analysis method is applied to extract solar 27-day signatures. A 27-day signature in NLC altitude can be identified in both hemispheres in the SCIAMACHY dataset, but the signature is more pronounced in the northern hemisphere. The solar signature in NLC altitude is found to be in phase with solar activity and temperature for latitudes ≳70°N. We provide a qualitative explanation for the positive correlation between solar activity and NLC altitude based on published model simulations.
    • 2018: Langowski, M. P., et al. “First results on the retrieval of noctilucent cloud albedo and occurrence rate from SCIAMACHY/Envisat satellite nadir measurements.” Journal of Atmospheric and Solar-Terrestrial Physics 175 (2018): 31-39. We present the first results on the retrieval of noctilucent cloud (NLC) albedosand occurrence rates from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartography) nadir data. The applicability of already available algorithms is discussed and necessary changes are reasoned. The occurrence rates for different latitude ranges are presented. During the summer period, when NLCs occur, the NLC occurrence rates show a maximum which is strongest at the highest latitudes. This is consistent with other observation methods. For the spring and autumn period, however, false NLC detections are observed at latitudes between 45°N and 65°N, where no NLCs are expected. The reason for this, and why it does not affect the retrieval during the NLC season is discussed. We also compared the SCIAMACHY nadir NLC occurrence rates with the ones retrieved from the SCIAMACHY limb measurements and the ones of SBUV and found qualitative agreement of these data sets.
    • 2018: Lübken, Franz‐Josef, Uwe Berger, and Gerd Baumgarten. “On the Anthropogenic Impact on Long‐Term Evolution of Noctilucent Clouds.” Geophysical Research Letters (2018). Little is known about climate change effects in the transition region between the Earth’s atmosphere and space, roughly at 80–120 km. Some of the earliest observations in this region come from noctilucent clouds (NLC) at ∼83‐km altitude. There is a long‐standing dispute whether NLC are indicators of climate change. We use model simulations for a time period of 138 years to study the impact of increasing CO2 and H2O on the development of NLC on centennial time scales. Since the beginning of industrialization the water vapor concentration mixing ratio at NLC heights has increased by ∼40% (1 ppmv) due to methane increase, whereas temperatures are nearly constant. The H2O increase has led to a large enhancement of NLC brightness. NLC presumably existed centuries earlier, but the chance to observe them by the naked eye was extremely small before the twentieth century, whereas it is likely to see several NLC per season in the modern era. Non-technical explanation for the layman: In our paper we address a problem that is controversially disputed since several decades, namely, whether noctilucent clouds (NLC) in the middle atmosphere are indicators of climate change. NLC are a spectacular optical phenomenon in the summer season at midlatitudes. We show in our paper that (i) NLC are indeed indicators of anthropogenic activity, (ii) the reason for this is increasing water vapor (caused by methane increase), which significantly enhances the visibility of NLC; and (iii) contrary to common understanding, cooling of the middle atmosphere due to increased reduces(!) the visibility of NLC. NLC constitute the earliest observations in this height region. In our model we expose 40 million dust/ice particles to long‐term changes in the middle atmosphere, namely, for 138 years starting with the beginning of industrialization. The model is nudged to the real world in the lower atmosphere. Since the beginning of industrialization,the chance to observe a bright NLC has increased from just one per several centuries(!) to a few per year. We conclude that NLC are indeed an indicator for climate change.
    • 2018: Dalin, P., et al. “Response of noctilucent cloud brightness to daily solar variations.” Journal of Atmospheric and Solar-Terrestrial Physics 169 (2018): 83-90. For the first time, long-term data sets of ground-based observations of noctilucent clouds (NLC) around the globe have been analyzed in order to investigate a response of NLC to solar UV irradiance variability on a day-to-day scale. NLC brightness has been considered versus variations of solar Lyman-alpha flux. We have found that day-to-day solar variability, whose effect is generally masked in the natural NLC variability, has a statistically significant effect when considering large statistics for more than ten years. Average increase in day-to-day solar Lyman-α flux results in average decrease in day-to-day NLC brightness that can be explained by robust physical mechanisms taking place in the summer mesosphere. Average time lags between variations of Lyman-α flux and NLC brightness are short (0–3 days), suggesting a dominant role of direct solar heating and of the dynamical mechanism compared to photodissociation of water vapor by solar Lyman-α flux. All found regularities are consistent between various ground-based NLC data sets collected at different locations around the globe and for various time intervals. Signatures of a 27-day periodicity seem to be present in the NLC brightness for individual summertime intervals; however, this oscillation cannot be unambiguously retrieved due to inevitable periods of tropospheric cloudiness.

     

    Excerpts from Mark Sagoff’s paper (links below to the Sagoff paper and related articles)

    https://www.researchgate.net/publication/316804306_Ecomodernism_and_the_Anthropocene

    https://nofrakkingconsensus.com/2018/07/06/anthropocene-the-medias-fake-geological-epoch/

    http://theconversation.com/enough-anthropocene-nonsense-we-already-know-the-world-is-in-crisis-43082

    geologic-epochs

    1. The origin of the term Anthropocene: The paper “Geology of Mankind,” published in 2002 calls on geologists “to use the term ‘Anthropocene’ for the current “human-dominated” geological epoch, that sits piggy-back on the Holocene.
    2. What does it mean? Anthropocene is a geologic epoch that recognizes that humanity has altered the “Earth system”.
    3. When did this geologic epoch start? They can’t agree on when the Anthropocene started. Was it the Neolithic Revolution? Was it the Industrial Revolution? Was it the nuclear bomb? Was it space travel? or was it way back when Europeans started navigating the seas and discovering and settling new lands?
    4. But aren’t geologic epochs much longer, millions of years? Yes. It took the God-like ego of man to divide the geological history into the Anthropocene and “everything that came before” and to recognize man not as just another species in Darwinism but a colossus so powerful that all other species and the planet itself is at its mercy.
    5. How long has mankind been here? Our current estimate is that the earth is more than 4.5 billion years old and in that context humanity’s tenure is an almost invisible flash in the pan.
    6. And that’s a geologic epoch? Yes, for such is man’s ego that he wants his own geologic epoch for a flash in that flash that started with the nuclear bomb.

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    3. The catastrophic consequences of anthropogenic global warming (AGW) are cited as melting glaciers and ice sheets, rising seas, and extreme weather. Examples of extreme weather include heat waves, droughts, floods, and super storms. The policy implication of this theory is that the catastrophic effects of AGW can be attenuated by reducing fossil fuel emissions (Hansen, 1981) (Hansen, 2016) (IPCCAR4, 2007) (IPCC, 2014) (Solomon, 2009) (Gillett, 2013) (Lacis, 2010).
    4. Accordingly, a global plan to control AGW was proposed in the Kyoto Protocol of 1997 and formalized into the United Nations Framework Convention on Climate Change (UNFCCC, 2014). The plan imposes a phased reduction of fossil fuel emissions on the Parties. It is based on the theory that warming is proportional to emissions and climate change is proportional to warming; and that therefore the catastrophic effects of climate change can and should be attenuated by reducing fossil fuel emissions (Lacis, 2010) (Botzen, 2008) (Allen, 2009) (Matthews, 2009) (IPCCAR4, 2007) (IPCC, 2014) (UNFCCC, 2016).
    5. A notable feature of the Kyoto Protocol/UNFCCC emission reduction plan is that the obligations of the Parties to the Framework Convention are defined by their classification into one of three groups described as Annex I, Annex II, and Non-Annex. The classification is based on whether the country is industrialized and whether it is a transition economy emerging from communism (UNFCCC, 2014). All industrialized countries are classified as Annex I and these countries are obligated to reduce their fossil fuel emissions according to a phased reduction plan (Obergassel, 2016) (UNFCCC, 2014).
    6. Non-industrialized developing countries are classified as Non-Annex and these Parties have no emission reduction obligation. The so called vulnerable countries form a sub-group of the Non-Annex countries. This group includes those developing countries that are deemed to be particularly susceptible to and least able to cope with the adverse effects of climate change. Special consideration is given to the Least Developed Countries (LDC) to ensure their inclusion in the vulnerable group. Annex II is a sub-group of Annex I. It contains only those industrialized countries that are not emerging from communism.
    7. In addition to emission reduction, Annex I countries have a further obligation to provide climate change adaptation assistance to vulnerable Non-Annex and LDC countries in the form of funding and technology transfer. The bulk of such assistance to Vulnerable Non-Annex and LDC (VNAL) countries is expected to derive from the adverse effects of extreme weather events such as tropical cyclones, droughts, floods, heat waves, and extreme cold (Kelly-Adger, 2000) (Adger, 2003) (Huq, 2004) (McGray, 2007).
    8. Initially, all such events in the VNAL countries were treated as fundable under the Framework Convention but recently it has been argued that this funding policy is arbitrary because natural variability is known to cause extreme weather events anyway even in the absence of fossil fuel emissions and that therefore not all extreme weather events can be attributed to fossil fuel emissions or and not all extreme weather events are relevant in the context of climate adaptation assistance from the Annex II countries to the VNAL countries (Allen, 2003). This principle was formalized in the Warsaw International Mechanism for Loss and Damage Associated with Climate Change Impacts (UNFCCC, 2013). This is where Event Attribution Science comes from.
    9. The Warsaw International Mechanism (WIM) has redefined climate change adaptation funding as a form of compensation for “loss and damage” suffered by the VNAL countries because of extreme weather events caused by fossil fuel emissions which are thought to be mostly a product of the industrialized countries. Accordingly, the WIM requires that loss and damage suffered by the VNAL countries for which compensation is sought from climate adaptation funds must be attributable to fossil fuel emissions.
    10. A probabilistic methodology was devised to address the need for attribution in the WIM and It has gained widespread acceptance in both technical and policy circles as a tool for the allocation of limited climate adaptation funds among competing needs of the VNAL countries (Stott, 2013) (Otto, 2015) (Otto, 2012) (James, 2014) (Trenberth, 2015) (Peterson, 2012) (Huggel, 2013). The probabilistic event attribution methodology (PEA) uses a large number of climate model experiments with multiple models and a multiplicity of initial conditions. A large sample size is used because extreme weather events are rare and their probability small by definition.
    11. The probability of an observed extreme weather event with anthropogenic emissions and the probability without anthropogenic emissions are derived from climate model experiments as P1 and P0. If the probability with emissions (P1) exceeds the probability without emissions (P0), the results are interpreted to indicate that emissions played a role in the occurrence of the event in question. Otherwise the event is assumed to be a product of natural variation alone. The probability that fossil fuel emissions played a role in the extreme weather event is represented as P = (P1-P0)/P0.
    12. A contentious issue in PEA analysis is that of uncertainty in the values of P0 and P1 and in the model results themselves. Policy analysts fear that large uncertainties of climate models (Oreskes, 1994) (Frame, 2011) (Curry, 2011) and shortcomings of the PEA methodology (Zwiers, 2013) (Hulme, 2011) provide sufficient reason to question the reliability of PEA to serve its intended function as a criterion for access to climate adaptation funds (Hulme, 2011). Mike Hulme argues that much greater statistical confidence in the PEA test is needed to justify denial of adaptation funding for loss and damage from weather extremes that do not pass the PEA test.
    13. Yet another concern with respect to the PEA methodology, and one that is the subject of this study, is the apparent tendency in climate science to extend the interpretation of PEA results beyond their intended function of climate adaptation fund allocation and into the realm of empirical evidence.
    14. It has long been claimed that basic principles of atmospheric physics imply that fossil fuel driven AGW will increase the frequency and severity of extreme weather events such as tropical cyclones, tornadoes, heat waves, extreme cold, droughts, floods, landslides, and even forest fires (IPCCAR4, 2007) (IPCCSREX, 2012) (IPCCAR5, 2014) (Easterling-Meehl, 2000) (Easterling-Evans, 2000) (Karl, 2003) (Min, 2011) (Allen, 2002) (Rosenzweig, 2001) (Mirza, 2003) (Coumou, 2012) (VanAalst, 2006) (Burton, 1997) (Flannigan, 2000) (Stocks, 1998) (Gillett N. , 2004). It is argued that the harm from these extreme weather effects of AGW provides scientific, ecological, social, political, and economic justification for urgent and costly reductions in fossil fuel emissions as a way of attenuating AGW because the social and economic cost of adaptation later is greater than the cost of mitigation now (Stern, 2006) (Metz, 2007) (IPCC, 2014).
    15. It is this catastrophic nature of AGW that provides the only rationale for the policy proposal of the Kyoto Protocol/UNFCCC that requires Annex I countries to reduce emissions by changing their energy infrastructure from fossil fuels to renewables (UNFCCC, 2014) (UNFCCC, 2016). And yet, this line of reasoning for reducing fossil fuel emissions and increasing investment in green renewable energy is weakened by a frustrating inability of climate science to produce empirical evidence that relates extreme weather disasters to emissions (IPCCSREX, 2012) (IPCCAR4, 2007) (Sheffield, 2008) (Bouwer, 2011) (Munshi, 2015) (IPCCAR5, 2014) (NCEI, 2015) (Woollings, 2014).
    16. Of particular note in this regard is that claims made by the IPCC in 2007 with regard to the effect of AGW on the frequency and intensity of tropical cyclones, droughts, and floods have been all but retracted in their very next Assessment Report in 2014 (IPCCAR5, 2014). Thus, climate scientists, though convinced of the causal connection between AGW and extreme weather events, are nevertheless unable to provide acceptable empirical evidence to support what to them is obvious and “unequivocal” (Curry, 2011) (Zwiers, 2013) (Munshi, 2016) (Frame, 2011) (Hulme, 2014).
    17. It is likely this frustration with the absence of trends in the historical data on extreme weather that motivated climate scientists to turn to PEA analysis as an alternative to empirical evidence of the extreme weather effects of AGW (WMO, 2016) (Stott, 2013) (Trenberth, 2015) (Otto, 2015). Thus, PEA results have been extrapolated and generalized well beyond the context of its narrow definition in terms of the WIM. Such extrapolation allows climate science to present positive PEA results as evidence that extreme precipitation, floods, droughts, heat waves, and cold spells are attributable to fossil fuel emissions (WMO, 2016) (Sneed, 2017). In keeping with its elevated status, the PEA methodology has been re-christened as Event Attribution Science or just Event Attribution. Here we show with the high profile example of the autumn floods of 2000 in England and Wales that this interpretation of PEA results (Stott, 2013) commits the fallacy of circular reasoning and that therefore positive PEA results by themselves do not constitute empirical evidence that AGW causes extreme weather events.
    18. Previously, critical commentaries on the PEA methodology have been published by Hulme, Boardman, Kelman and others (Hulme, 2011) (Hulme, 2014) (Boardman, 2008) (Boardman, 2003) (Kelman, 2001). Mike Hulme’s work exposes the weaknesses and the limits of the PEA methodology, John Boardman shows that the PEA methodology had erroneously ascribed non-meteorological aspects of the floods to climate change, and Kelman exposes certain inconsistencies in the details of the flood data and what had been assumed in the Event Attribution climate model analysis.
    19. This work describes Event Attribution Science in a case study format using the high profile example of the Event Attribution analysis of the floods in England and Wales in the year 2000 by (Pall, 2011). A critical evaluation of these interpretations is made in light of the relevant precipitation data (Met Office, 2017) and non-meteorological factors that affect flood impact severity (Boardman, 2003) (Boardman, 2008). The use of the Event Attribution Science to present evidence of the effect of fossil fuel emissions on the severity of extreme weather events is evaluated in this context.
    20. In mid-September of the year 2000 an unrelenting sequence of rainstorms began to strike in various parts of England and Wales. By mid-October flooding became widespread and devastating. The rainstorms and floods continued in multiple sequential flooding events until mid-December (Kelman, 2001) (Marsh, 2001) (Marsh, 2002). The series of rainstorms taken together is considered to be a rare and extreme meteorological event in terms of the amount of precipitation, the duration, and the high runoff rates in all the rivers in the region and considered to be a consequence of climate change (Reynard, 2001) (Pall, 2011).
    21. A study of the autumn 2000 floods by Terry Marsh found that 640 mm of rain fell in the four months of rain ending December 15, 2000 and 1033 mm of rain fell in the eight months ending in April 2001. By both measures, the year 2000 ranks first in the 235-year data record going back to 1766 (Marsh, 2001). An estimate of the total volume of water delivered to the ground by the rainstorms is also reported in the Marsh study in terms of the combined flows of the Rivers Thames, Severn, Welsh Dee, and Wharfe. By this measure the year 2000 ranked second after 1947 for 10-day and 30-day outflows and first, just ahead of 1947, for 60-day and 90-day outflows (Marsh, 2001). Marsh also points out that the 2000 floods did not occur in isolation. They fall in the middle of cluster of flood years in the area prior to 2000 that includes 1989, 1993, 1994, and 1998 and since 2000 in 2007, 2013-2014, and 2015-2016 (Marsh, 2001) (Marsh, 2002) (Marsh, 2007) (Huntingford, 2014) (Schaller, 2016) (Marsh, 2016).
    22. These storm and precipitation events came to be thought of as extreme and unnatural and research interest turned to the effect of human influences in the form of anthropogenic global warming and climate change on the apparent unnatural increase in the frequency and intensity of floods in the UK (Reynard, 1996) (Reynard, 1998) (Reynard, 2001) (Macklin, 2003) (Wilby, 2008). It was in this context that the newly minted Event Attribution methodology was applied to the autumn floods of 2000 using an array of climate models and a large sample of climate model runs.
    23. The results showed that the 2000 floods were more likely in “the world as it is” (with fossil fuel emissions) than in “the world that might have been” without fossil fuel emissions. Based on this PEA result the autumn floods of 2000 in England and Wales were attributed to climate change and indirectly to fossil fuel emissions (Pall, 2011).
    24. However, the attribution of the floods to emissions remains controversial. First, floods are not purely meteorological events because important non-meteorological factors play a role in the intensity and devastation of flooding at any given level of rainfall (Kelman, 2001) (Boardman, 2003) (Boardman, 2008) (Boardman, Don’t blame the climate, 2008). Also, the known large natural variability in precipitation in England and Wales provides a simpler explanation of extreme flooding events than the effect of anthropogenic carbon dioxide emissions found in climate models (Kay, 2009) (Shackley, 1998) (Young, 1996) (Beder, 1999) (Curry, 2011) (Frame, 2011) (Hulme, 2014) (Deser, 2012).
    25. This case study examines patterns in the 251-year record of precipitation in England and Wales from 1766 to 2016 in the context of the conclusions drawn from PEA analysis about the autumn floods of 2000 in England and Wales and considers whether a simpler and more natural explanation exists for this precipitation event. Historical monthly mean precipitation data for England and Wales are provided by the Met Office of the Government of the UK (MetOffice, 2017). Precipitation data are recorded in millimeters of water equivalent at standard conditions in a continuous annual time series for a 251-year period from 1766 to 2016 for each of the twelve calendar months.
    26. The data along with their OLS linear trends are depicted graphically, month by month, in Charts1-6 below the text in the chart section of this post. We note in these figures that the calendar months differ significantly in terms of mean monthly precipitation, the variance of precipitation, and the overall trend in the study period. These differences (highlighted in Charts 7-8) show that mean monthly precipitation characteristics differ markedly among the calendar months. On average, autumn is the wettest and spring the driest. Summer and winter lie in between with winter wetter than summer. Year to year variability in precipitation is also different among the calendar months. Charts 9-14 show large differences among the calendar months in standard deviations measured in a moving 30-year window. The generational (30-year) time scale is generally used in the study of climate phenomena (Ackerman, 2006) (WMO, 2016). The red line in these charts marks the no-trend boundary between rising and declining trends.
    27. To maintain the integrity of these observed differences, monthly mean precipitation data are not combined. Instead each month is studied in isolation as a phenomenon of nature unique to that month. A benefit of this methodology is that it facilitates the interpretation of historical trend analysis in terms of the season of the floods under study.
    28. Outlier analysis is carried out by examining the ten largest values from each time series one at a time starting with the largest and moving sequentially to the smallest. At each step a hypothesis test is used to determine whether the value removed belongs to the distribution of all values that are less than the value removed. The null hypothesis is H0: testValue ≤ mean(all values less than the test value). If the null hypothesis is rejected the test value is marked as an outlier and described as an extreme year (Dixon, 1950) (Aggarwal, 2015). The procedure is carried out separately for each calendar month.
    29. A generational (30-year) moving window is used to compute a time series of 221 variability measures for each calendar month. Variability is expressed as the standard deviation and studied for trends. A statistically significant rising trend in this series is expected if climate change is causing the precipitation series to become more volatile. Statistical significance is determined using classical hypothesis testing at a maximum false positive error rate of α=0.001 consistent with “Revised Standards for Statistical Evidence” published by the National Academy of Sciences to address an unacceptably large proportion of irreproducible results in published research (Johnson, 2013) (Siegfried, 2010).
    30. The proposition that anthropogenic CO2 emissions since the Industrial Revolution have increased the amount of precipitation in England and Wales implies that the study period 1766-2016 should show a statistically significant rising trend in precipitation amounts. The simple OLS trend lines for mean monthly precipitation amounts are shown in Charts 1-6. Only three out of the twelve calendar months show a statistically significant trend. The winter months of December and January show the required rising trend in precipitation while the summer month of July shows a declining trend. No evidence of a trend in mean monthly precipitation amount is found in the other nine calendar months.
    31. To explain the autumn 2000 floods in England and Wales in terms of trends, a positive trend is necessary for the four months from September to and December. A positive result for December alone does not provide sufficient evidence that rising trends in the amount of precipitation were responsible for the floods of 2000. It is also noted that the summer floods of 2007 appear anomalous in this line of reasoning as the only evidence of a trend in the summer months is a declining trend for July. The event attribution finding that the autumn floods of 2000 were caused by climate change is consistent with historical record.
    32. Charts 9-14 are graphical displays of the standard deviation of mean monthly precipitation in a generational moving window. The results provide evidence that mean monthly precipitation in the autumn months of October and November, the winter months of January and February, and the spring month of March have become more volatile over the study period. The summer month of July shows a decreasing trend in volatility and the other six months show no evidence of a trend in volatility.
    33. The evidence of rising volatility in the months of October and November might have been consistent with the attribution of the floods of 2000 to climate change had the volatility been associated with greater precipitation. Without evidence of a rising trend in precipitation in these months it is unclear whether the greater variance relates to extreme dry years or extreme wet years. To explain floods in terms of climate change evidence of more extreme wet years is necessary.
    34. A search for extreme wet years is made by using outlier analysis. For the purpose of this analysis, a wet year is deemed to be extreme if it is an outlier in the context of all years in the time series with less precipitation. The analysis begins with the identification of the ten highest precipitation years for each calendar month. They are shown in Charts 15-20. Each of the ten wettest years is tested against all years with less rainfall to determine if it is an outlier in the sense that it does not belong in the distribution of the comparison series. These hypothesis tests are carried out at a maximum false positive error rate of α=0.001. Since twelve tests are made the overall study-wide false positive error rate is approximately 0.012 or 1.2% (Holm, 1979). Statistically significant results are identified with filled markers. These outliers are deemed to be extreme precipitation years.
    35. February, September, November, and December contain no extreme years. The other eight months contain at least one extreme wet year. April contains four, May contains three, and March and August contain two each. January, July, and October contain only one extreme year. For the autumn floods of 2000, the relevant months are September, when the rains started, and October, November, and December when they continued and intensified. Only one extreme event is found for these months and it occurred in October 1903 with 218 mm of precipitation. October of 2000 is indeed the second wettest October on record with 188 mm of precipitation but it is not an outlier as 188 mm is well within expected variability of the distribution of October precipitations at α=0.001.
    36. These results, together with the absence of a rising trend in precipitation amount or volatility show no empirical support for the claim made with Event Attribution analysis that the autumn 2000 floods were caused by extreme precipitation events attributable to anthropogenic CO2 emissions. In terms of the cluster of flood years in the UK in the period 1989 to 2015, the only extreme year that occurs in the same season as the floods is the extreme for January in the year 2014 because it coincides with the winter 2013-2014 floods. The years 2000 and 2012 are also found in the list of extremes in Figure 10 but not in the season of the floods in those years.
    37. The presentation of empirical evidence for a given theory proceeds as follows. First, a testable implication of the theory is deduced. Then, data are collected, either experimental data or field data. The data must be independent of the theory and their collection must be unbiased. In the case of classical hypothesis testing, the testable implication is then tested against the data with the null hypothesis that the theory is false. If the null hypothesis is rejected, the data constitute empirical evidence in support of the theory (Popper, 2005) (Pearl, 2009) (Kothari, 2004).
    38. In the case of Event Attribution analysis with climate models, the results serve the intended purpose of providing a non-subjective method for the allocation of climate adaptation funds in accordance with WIM guidelines. However, their further interpretation as evidence of the extreme weather effects of fossil fuel emissions involves circular reasoning because climate model results are not data independent of the theory but a mathematical expression of the theory itself; and the selection of specific events to test for event attribution contains a data collection bias (Munshi, 2016) (Koutsoyiannis, 2008) (VonStorch, 1999).
    39. Yet another contentious issue in event attribution with climate models is the known chaotic behavior of climate that is not contained in climate models. Non-linear dynamics and chaos is discussed in a related post: IS CLIMATE CHAOTIC?

    CHARTS 1-6: OLS LINEAR TRENDS ACROSS THE FULL SAMPLE

    fig1-1fig1-2fig1-3fig1-4fig2-1fig2-2

    CHARTS 7-8: A COMPARISON OF THE 12 CALENDAR MONTHS

    fig3-1fig3-2

    CHARTS 9-14: STANDARD DEVIATION IN A MOVING 30-YEAR WINDOW

    fig5-1

    fig5-2fig5-3fig5-4fig6-1fig6-2

    CHARTS 15-20: EXTREME VALUES AND OUTLIERS

    fig8-1

    fig8-2

    fig8-3

    fig8-4

    fig9-1

    fig9-2

     

     

     

     

    Gerald Marsh, retired Argonne National Laboratories Physicist, challenges the usual assumption that ice age cycles are initiated by Milankovich Cycles and driven by the Arrhenius effect of carbon dioxide. He says that the key variable here is “low altitude cloud cover” driven by cosmic rays. A paper worth reading.

    ABSTRACT

    1. The existing understanding of interglacial periods is that they
      are initiated by Milankovitch cycles enhanced by rising atmospheric
      carbon dioxide concentrations. During interglacials, global temperature is
      also believed to be primarily controlled by carbon dioxide concentrations,
      modulated by internal processes such as the Pacific Decadal Oscillation
      and the North Atlantic Oscillation. Recent work challenges the
      fundamental basis of these conceptions.
    2. INTRODUCTION
      The history of the role of carbon dioxide in climate begins with the work of Tyndall 1861 and later in 1896 by Arrhenius. The concept that carbon dioxide controlled climate fell into disfavor for a variety of reasons until revived by Callendar in 1938. It came into full favor after the work of Plass in the mid-1950s. Unlike what was believed then, it is known today that for Earth’s present climate water vapor is the principal greenhouse gas with carbon dioxide playing a secondary role. Climate models nevertheless use carbon dioxide as the principal variable while water vapor is treated as a feedback. This is consistent with, but not mandated by, the Assumption that—except for internal processes—the temperature during Interglacials is dependent on atmospheric carbon dioxide concentrations. It now appears that this is not the case: interglacials can have far higher global temperatures than at present with no increase in the concentration of carbon dioxide.
    3. GLACIAL TERMINATIONS AND CARBON DIOXIDE
      Even a casual perusal of the data from the Vostok ice core gives an appreciation of how temperature and carbon dioxide concentration change synchronously. The role of carbon dioxide concentration in the initiation of interglacials, during the transition to an interglacial, and its control of temperature during the interglacial is not yet entirely clear. Between glacial and interglacial periods the concentration of atmospheric carbon dioxide varies between about 200-280 ppm being at ~280 ppm during interglacials.
    4. OCEAN-ATMOSPHERE CO2 EXCHANGE: The details of the source of these variations is still somewhat controversial, but it is clear that carbon dioxide concentrations are coupled and in equilibrium with oceanic changes. The cause of the glacial to interglacial increase in atmospheric carbon dioxide is now thought to be due to changes in ventilation of deep water at the ocean surface around Antarctica and the resulting effect on the global efficiency of the “biological pump”.
    5. INTERGLACIAL CO2 CONCENTRATION: A perusal of the interglacial carbon dioxide concentrations tell us that the process of increased ventilation coupled with an increasingly productive biological pump appears to be self-limiting during interglacials, rising little above ~280 ppm, despite warmer temperatures in past interglacials. This mechanism for glacial to interglacial variation in carbon dioxide concentration is supported by the observation that the rise in carbon dioxide lags the temperature increase by some 800-1000 years—ruling out the possibility that rising carbon dioxide concentrations were responsible for terminating glacial periods.
    6. MILANKOVITCH INSOLATION THEORY: As a consequence, it is now generally believed that glacial periods are terminated by increased insolation in polar regions due to quasi-periodic variations in the Earth’s orbital parameters. And it is true that paleoclimatic archives show spectral components that match the frequencies of Earth’s orbital modulation.
    7. PROBLEMS WITH THE MILANKOVITCH THEORY: This Milankovitch insolation theory has a number of problems associated with it, in particular, the so called “causality problem”; i.e., what came first—increased insolation or the shift to an interglacial. This would seem to be the most serious objection, since if the warming of the Earth preceded the increased insolation it could not be caused by it. This is not to say that Milankovitch variations in solar insolation do not play a role in changing climate, but they could not be the principal cause of glacial terminations.
    8. THE PENULTIMATE ICE AGE: Consider the timing of the termination of the penultimate ice age (Termination II) some 140 thousand years ago. The data from Devils Hole (DH), Vostok, and the d18O SPECMAP record show  that Termination II occurred at 140±3 ka; the Vostok record gives 140±15 ka; and the SPECMAP gives 128±3 ka.9. The latter is clearly not consistent with the first two. The reason has to do with the origin of the SPECMAP time scale. The SPECMAP record was constructed by averaging d18O data from five deep-sea sediment cores. The result was then correlated with the calculated Insolation cycles.
    9. Devils Hole (DH) is an open fault zone in south-central Nevada. A superposition of DH-11, Vostok, and SPECMAP curves for the period 160 to 60 ka in comparison with June 60N insolation over the last 800,000 years shows that sea levels were at or above modern levels before the rise in solar insolation often thought to initiate Termination II. The SPECMAP chronology must therefore be adjusted when comparisons are made with records not dependent on the SPECMAP timescale. The above considerations imply that Termination II was not initiated by an increase in
      carbon dioxide concentration or increased insolation. The question then remains: What did initiate Termination II?
    10. Kirkby, et al. found was that “the warming at the end of the penultimate ice age was underway at the minimum of 65N June insolation, and essentially complete about 8 kyr prior to the insolation maximum”.
    11. ROLE OF COSMIC RAY FLUX: The data strongly imply that Termination II was initiated by a reduction in cosmic ray flux. Such a reduction would lead to a reduction in the amount of low-altitude cloud cover thereby reducing the Earth’s albedo with a consequent rise in global temperature.
    12. There is another compelling argument that can be given to support this hypothesis. Sime,et al found that past interglacial climates were much warmer than previously
      thought. Their analysis of the data shows that the maximum interglacial temperatures over the past 340 kyr were between 6C and 10C above present day values. Past interglacial carbon dioxide concentrations were not higher than that of the current interglacial, and therefore carbon dioxide could not have been responsible for this warming.
    13. The fact that carbon dioxide concentrations were not higher during periods of much warmer temperatures confirms the self-limiting nature of the process driving the rise of carbon dioxide concentration during the transition to interglacials; that is, where an increase in the ventilation of deep water at the surface of the Antarctic ocean and the resulting effect on the efficiency of the biological pump cause the glacial to interglacial rise carbon dioxide.
    14. If it is assumed that solar irradiance during past interglacials was comparable to today’s value (as is assumed in the Milankovitch theory), it would seem that the only factor left—after excluding increases in insolation or carbon dioxide concentrations—that could be responsible for the glacial to interglacial transition is a change in the Earth’s albedo. During glacial periods, the snow and ice cover could not melt without an increase in the energy entering the climate system. This could occur if there was a decrease in albedo caused by a decrease in cloud cover.
    15. THE EARTH’S LOW CLOUD ALBEDO: The Earth’s albedo is known to be correlated with galactic cosmic-ray flux. This relationship is clearly seen over the eleven-year cycle of the sun. There is a very strong correlation between galactic cosmic rays, solar irradiance, and low cloud cover. Note that increased lower cloud cover (implying an increased albedo) closely follows cosmic ray intensity.
    16. VARIATION IN GALACTIC COSMIC RAY FLUX: It is generally understood that the variation is galactic cosmic ray flux is due to changes in the solar wind associated with solar activity. The sun emits electromagnetic radiation and energetic particles known as the solar wind. A rise in solar activity—as measured by the sun spot cycle—affects the solar wind and the inter-planetary magnetic field by driving matter and magnetic flux trapped in the plasma of the local interplanetary medium outward, thereby creating what is called the heliosphere and partially shielding this volume, which includes the earth, from galactic cosmic rays—distinct from solar cosmic rays, which have much less energy.
    17. When solar activity decreases, with a consequent small decrease in irradiance, the number of galactic cosmic rays entering the earth’s atmosphere increases as does the amount of low cloud cover. This increase in cloud cover results in an increase in the earth’s albedo, thereby lowering the average temperature. The sun’s 11 year cycle is therefore not only associated with small changes in irradiance, but also with changes in the solar wind, which in turn affect cloud cover by modulating the cosmic ray flux.
    18. CLOUD ALBEDO: This, it is argued, constitutes a strong positive feedback needed to explain the significant impact of small changes in solar activity on climate. Long-term changes in cloud albedo would be associated with long-term changes in the intensity of galactic cosmic rays. The great sensitivity of climate to small changes in solar activity is corroborated by the work of Bond, et al., who have shown a strong correlation between the cosmogenic nuclides 14C and 10Be and centennial to millennial changes in proxies for drift ice as measured in deep-sea sediment cores covering the Holocene time period.
    19. MODULATION OF GALACTIC COSMIC RAY FLUX: The production of these nuclides is related to the modulation of galactic cosmic rays, as described above. The increase in the concentration of the drift ice proxies increases with colder climates. These authors conclude that Earth’s climate system is highly sensitive to changes in solar activity. For cosmic ray driven variations in albedo to be a viable candidate for initiating glacial terminations, cosmic ray variations must show periodicities comparable to those of the glacial/interglacial cycles (Kirkby, etal).
    20. The mechanism for the modulation of cosmic ray flux discussed above was tied to solar activity, but the 41 kyr and 100 kyr cycles seen correspond with the small quasiperiodic changes in the Earth’s orbital parameters underlying the Milankovitch theory. For these same variations to affect cosmic ray flux they would have to modulate the geomagnetic field or the shielding due to the heliosphere.
    21. Although the existence of these periodicities and the underlying mechanism are still somewhat controversial, the lack of a clear understanding of the underlying theory does not negate the fact that these periodicities do occur in galactic cosmic ray flux. If cosmic ray driven albedo change is responsible for Termination II, and a lower albedo was also responsible for the warmer climate of past interglacials—rather than higher carbon dioxide concentrations—the galactic cosmic ray flux would have had to be lower during past interglacials than it is during the present one. That this appears to be the case is suggested by the record.
    22. ORBITAL FORCING OF GEOMAGNETIC FIELD INTENSITY: With regard to orbital forcing of the geomagnetic field intensity, it is found that “Despite some indications from spectral analysis, there is no clear evidence for a significant orbital forcing of the paleointensity signals”, although there were some caveats. In terms of the galactic cosmic ray flux, Kirby, et al. maintain that “. . . previous conclusions that orbital frequencies are absent were premature”. An extensive discussion of “Interstellar-Terrestrial Issues” has also been
      given by Scherer, et al.
    23. Using the fact that the galactic cosmic ray flux incident on the heliosphere boundary is known to have remained close to constant over the last 200 kyr, and that there exist independent records of geomagnetic variations over this period, Sharma was able to use a functional relation reflecting the existing data to give a good estimate of solar activity over this 200 kyr period.
    24. The atmospheric production rate of 10Be depends on the geomagnetic field intensity and the solar modulation factor—the energy lost by cosmic ray particles traversing the heliosphere to reach the Earth’s orbit (this is also known as the “heliocentric potential”, an electric potential centered on the sun, which is introduced to simplify calculations by substituting electrostatic repulsion for the interaction of cosmic rays with the solar wind).
    25. SUMMARY: It has been shown above that low altitude cloud cover closely follows cosmic ray flux; that the galactic cosmic ray flux has the periodicities of the glacial/interglacial cycles; that a decrease in galactic cosmic ray flux was coincident with Termination II; and that the most likely initiator for Termination II was a consequent decrease in Earth’s albedo. The temperature of past interglacials was higher than today most likely as a consequence of a lower global albedo due to a decrease in galactic cosmic ray flux reaching the Earth’s atmosphere. In addition, the galactic cosmic ray intensity exhibits a 100 kyr periodicity over the last 200 kyr that is in phase with the glacial terminations of this period. Carbon dioxide appears to play a very limited role in setting interglacial temperature.
    26. GERALD MARSH is a physicist, retired from Argonne National Laboratory, who has worked and published widely in the areas of science, nuclear power, and foreign affairs. He was a consultant to the Department of Defense on strategic nuclear technology and policy in the Reagan, Bush, and Clinton administrations, and served with the U.S. START delegation in Geneva. He is a Fellow of the American Physical Society.
    27. SOURCE DOCUMENT: Arxiv.org: Source Document
    1. Sir GEORGE SIMPSON
    2. Sir Simpson noted that the first place he thought it was not sufficiently realized by non-meteorologists who came for the first time to help the Society in its study, that it was impossible to solve the problem of the temperature distribution in the atmosphere by working out the radiation. The atmosphere was not in a state of radiative equilibrium, and it also received heat by transfer from one part to another.
    3. In the second place, one had to remember that the temperature distribution in the atmosphere was determined almost entirely by the movement of the air up and down. This forced the atmosphere into a temperature distribution which was quite out of balance with the radiation. One could not, therefore, calculate the temperature effect of changing any one factor in the atmosphere, and he felt that the actual numerical results which Mr. Callendar had obtained could not be used to give a definite indication of the order of magnitude of the effect.
    4. Thirdly, he thought Mr. Callendar should give a little more information as to how he had calculated the results shown in Fig. 2. These contained the crucial point of the paper, but the paper did not explain how they were obtained.
    5. In Table 5 Mr. Callendar had given the effect of doubling the CO2, in one band, 13 to 16, which included nearly the whole of the energy connected with the C02. The increase of temperature obtained by calculation from these results, however, was not the same for a similar increase in CO2, as that shown in Fig. 2. This sort of discrepancy should be cleared up.
    6. Lastly he thought that the rise in CO2 content and temperature during the last 50 years, must be taken as rather a coincidence. The magnitude of it was even larger than Mr. Callendar had calculated, and he thought the rise in temperature was probably only one phase of one of the peculiar variations which all meteorological
      elements experienced.
    7. Dr. F. J. W. WHIPPLE
    8. Dr. Whipple expressed the hope that the author would give the Society an account of his investigation of the natural movements of carbon dioxide. It was not clear how the calculations regarding the gradual diffusion of C02 into the sea were carried out.
    9. The calculations embodied in Table IV depended on the assumption of high lapse rates of temperature everywhere. The inversions it seemed necessary to make additional calculations to allow for the varying circumstances. Other processes besides radiation are involved in the exchange of normal energy between ground and atmosphere, but it may be justifiable to ignore these other processes in an investigation of the effect of variations in the amount of CO2.
    10. Prof. D. BRUNT
    11. Prof. Brunt referred to the diagrams showing the gradual rise of temperature during the last 30 years, and said that this change in the mean temperature was no more striking than the changes which appear to have occurred in the latter half of the 18th century, and whose reality does not appear to be a matter of defective instruments.
    12. The long series of pressure observations made in Paris showed clearly that there had been great changes in the mean path of depressions coming from the Atlantic.
    13. Prof. Brunt agreed with the view of Sir George Simpson that the effect of an increase in the absorbing power of the atmosphere would not be a simple change of temperature, but would modify the general circulation, and so yield a very complicated series of changes in conditions. He was not quite clear how the temperature changes had been evaluated. He appreciated, however, that Mr. Callendar had put a tremendous amount of work into his most interesting paper.
    14. Dr. C. E. P. BROOKS
    15. Dr Brooks said that he had no doubt that there had been a real climate change during the past thirty or forty years. This was shown not only by the rise of temperature at land stations, but also by the decrease in the amount of ice in Arctic and probably also in Antarctic regions and by the rise of sea temperatures.
    16. This rise of temperature could however he explained, qualitatively if not quantitatively, by changes in the atmospheric circulation, and in those regions where a change in the circulation could be expected to cause a fall of temperature, there had actually been a fall.
    17. Moreover the rise of temperature was about ten times as great in the arctic regions as in middle or low latitudes, and he did  not think that a change in the amount of carbon dioxide could cause such a differential effect. The possibility certainly merited discussion, however, and he welcomed the paper as a valuable contribution to the problem of climatic change.
    18. Mr. I,. M. G. DINES
    19. Mr Dines asked Mr. Callendar whether he was satisfied that the change in the temperature of the air which he had found was significant, and that it was not merely a casual variation.
    20. Mr. J. H. COSTE
    21. Mr. Coste congratulated Mr. Callendar on his courage and perseverance. He would like to raise some practical issues.
    22. Firstly, was the C02 in the air really increasing? It used to be given as 400 ppm then as methods of chemical analysis improved it went down to 300 ppm, and he thought it was very doubtful whether the differences which Mr. Callendar made use of were real. The methods of determining C02 thirty or forty years ago were not sufficiently accurate for making such a comparison.
    23. A. Krogh
    24. Mr Krogh calculated that for a constant difference in tension in the atmosphere between the air and the ocean, the latter being less rich, the annual invasion of C02 would be equal to 3 x 108 metric tons, which was about the annual contribution of CO2 to the atmosphere by the burning of fuel; to this absorption by the ocean must be added the effects of vegetation, by photosynthesis. Thermometers thirty years
      ago were not instruments of very high precision and one would hesitate to consider variations of fractions of a degree based on observations made with such thermometers.
    25. G. S. CALLENDAR
    26. in replying, Mr. G. S. Callendar said he realized the extreme complexity of the temperature control at any particular region of the earth’s surface and also that radiative equilibrium was not actually established, but if any substance is added to the atmosphere which delays the transfer of low temperature radiation, without interfering with the arrival or distribution of the heat supply, some rise of temperature appears to be inevitable in those parts which are furthest from outer space.
    27. As stated in the paper that the variation of temperature with CO2 (Fig. 2), was obtained from the values of sky radiation, calculated for different amounts of this gas, substituted in expression 5. If the changes in S  shown in Table V are used for expression 5, it will be found that the temperature changes lie on the curve of Fig. 2 when the total sky radiation is 7/10 of the surface radiation. The sky radiation is calculated as a proportion of that from the surface, hence, at constant heat supply, a change of sky temperature involves an equilibrium change of surface temperature as in expression 5.
    28. It was found that even the minimum numerical explanation of the method used for calculating sky radiation would occupy several pages, and as a number of similar methods have been published from time to time, it was decided to use the available space for matter of more direct interest.
    29. In reply to Dr. Whipple, the author regretted that space did not permit an account of the natural movements of CO2 (old English for the Carbon Cycle). He had actually written an account of these, but it was eight times as long as the present paper (and therefore it was not included in the paper).
    30. For the calculation of the diffusion of CO2 into the sea the effective depth was considered to be 200 meters at any one time.
    31. The effect of CO, on temperatures has been calculated for a variety of lapse rates, including large inversions. In the latter case the effect on the surface temperature is small, but the protection for the warm middle layers remains.
    32. In reply to Prof. Brunt, the author stated that the warm periods of 1780, 1797, and 1827 appeared to be of the nature of short warm intervals of up to 10 years, with some very cold years intervening, whereas recent conditions indicated a more gradual and sustained rise of temperature; this was perhaps best shown by a 40-year moving average.
    33. In reply to Dr. Brooks, the author agreed that the recent rise in Arctic temperatures was far too large to be attributed to change of CO2. He thought that the latter might act as a promoter to start a series of imminent changes in the northern ice conditions. On account of their large rise he had not included the Arctic stations in the world temperature curve (Fig. 4).
    34. In reply to Mr. Dines, the author said he thought the change of air appeared too widespread to be a casual change due to local variations of pressure.
    35. In reply to Mr. Coste, the author said that the early series of CO2 measurements he had used were probably very accurate; he had only observed on days when strong and steady west winds were blowing at Kew. The actual CO2 added in the last 40 years was equal to an increase of 8%; the observed and calculated values agreed in
      giving an effective increase of about 6% at Kew.
    36. The author is not aware of the solution coefficients for sea water used by A. Krogh to give the stated figure which appears to be far too high. It must be remembered that less than 1/1000 of the sea volume would be replaced at the surface in one year, and the annual increase of CO2 pressure in the air is less than 1/10^6 atmosphere.
    37. About 98% of the CO2 used by vegetation appears to be returned by decay oxidation and respiration.
    38. The author thought that very accurate temperatures were taken last century; if there was any doubt on this point the introduction to the long period tables from the Radcliffe Observatory (Met. Obs., Vol. 55, 1930), should set this at rest.
    39. With regard to the effect of vertical motion on the “ geostrophic departure ” of the wind, in section 7 of our paper “ The importance of vertical motion in the
      development of tropical revolving storms (old English for tropical cyclones),” published in the lournal January, 1938, a general proposition is enunciated, which reads as follows: “ If vertical motion occurs in the atmosphere in a region of horizontal temperature gradient, then ascending motion gives a component
      of wind from warm to cold, and descending motion a component front
      cold to n arm. ”
    40. We are indebted to Prof. Brunt for pointing out that the brief argument given in the paper does not stress at all adequately the type of air motion to which the proposition is intended to apply, and that it certainly does not apply to the case of a convection current rising by instability through an environment.
    41. By not realizing this natural application of the proposition, we failed fully to appreciate Prof. Brunt’s contribution to the discussion of the paper, and in order to avoid further misunderstanding, we should like to amend the statement to read :
      “ If there is general vertical motion in a region where the winds
      are quasi-geostrophic, then the departure of the wind velocity from the
      geostrophic value has a component directed along the horizontal gradient
      of temperature, from warm to cold with ascending motion, and from
      cold to warm with descending motion.”
    42. The proposition is believed to have an important bearing on general
      meteorological developments, where gradual ascending motion, as, for
      example, in a frontal zone, is associated with convcrgence or divergence,
      and with departures of the wind velocity from the geostrophic value.
      Although the departures are generally small compared with the
      geostrophic velocities (so that the whole motion may be described as
      qllasi-geostrophic) they are of fundamental dynamical significance.
      A further paper will shortly be presented, in which the mathematical
      and physical basis of the proposition will receive a more adequate treatment.
    43. FULL TEXT OF THE PAPER IN PDF: CALLENDAR 1938 PDF