Glacier mass balance
Posted July 23, 2010on:
The dynamics of glaciers that feed rivers are best understood in terms of a mass balance which states essentially that
input – output = accumulation.
The input term is usually the amount of precipitation in the glacial basin that flows to the glacier. The output term is the meltwater that feeds the river plus evaporation. If the accumulation is positive the glacier is growing and if it is negative it means that the glacier is shrinking.
If it is shrinking it could mean one of two things. Either the amount of precipitation is declining relative to the melt rate; or the melt rate is increasing relative to precipitation. There is a big difference between these two scenarios in terms of water flow in downstream rivers.
In the former case, the water flow in downstream rivers would remain unchanged while in the latter case, there would be an increase in flow possibly associated with rising river levels and flooding. In the absence of rising river levels downstream, it is not possible to conclude that the glacier is retreating because of an increase in the melt rate.
Yet, all instances of glacial retreat are presented by the IPCC as an effect of increased melt rate caused by global warming without providing the necessary data on changes in the flow rates of downstream rivers that the glacier feeds.