Glaciers have been in the news a lot recently after the IPCC mistakenly claimed that those in the Himalayas would disappear by 2035. Despite this it has often been reported in the mainstream media that the Earth’s glaciers are retreating in response to man-made global warming. A new study shows, as is often the case with such sweeping claims, that the reality is more complicated with mankind’s influence probably not the major factor.
With the possible exception of the glaciers in Scandinavia the glaciers on the Alps are the most well observed on Earth. For more than 100 years the Swiss glaciers have been observed, new topographic maps compiled, aerial photographs taken and measurements made.
According to researchers at least half of the loss of the Aletch glacier in Switzerland, which has receded by 2,000 metres in the past century, is due to natural climatic variability. The researchers, from the University of Fribourg in Switzerland, say that their findings are generally true for the majority of glaciers worldwide. The research has been described as the first detailed scrutiny of the many forces that affect the behavior of glaciers.
It is possible to use historical data to make some judgment of the influence of natural variations on glacier size although such data are rather sparse compared to the measurements obtained in the last century or so. It is worth noting that during the Roman Warm Period Hannibal’s crossing of the Alps shows that 2,200 years ago the glaciers were much smaller than they are today.
Matthias Huss and colleagues gather about 10,000 observations of glaciers in the Swiss Alps (daily ice melt, snow accumulation, ice and snow volume) made over the past 100 years and used them to create a computer model of some 30 glaciers.
Visible in the data was the influence of the very poorly understood Atlantic Multidecadal Oscillation (AMO) – a regular change in sea surface temperatures on timescales of up to 60 years or more.
The glaciers studied generally lost mass during the 20th century although there were brief periods of mass gain in the second decade and in the 1970’s. In the 1940’s and since 1980 mass has been lost as more precipitation fell as rain rather than snow.
Last December, Huss published a study that showed that Swiss glaciers melted at a faster rate in the 1940’s than they do nowadays, and that glacier melting is influenced by long-term changes in solar radiation.
In another paper Chunzai Wang et al show that the AMO variation can be detected in the atmospheric concentration of CO2 as measured at Hawaii and the South Pole since 1958. There is a strong seasonal effect in the data as well as the well-know long term trend but when these are taken into account there is a low in CO2, about 2 parts per million below the 1958-2008 average, between the late 1960s and the mid-1990s. This is coincident with a cool phase of the AMO.
In conclusion, the Swiss Alps now join Mt Kilimanjaro as having had a misleading press. We now know that Mt Kilimanjaro’s dramatic shrinkage of its summit glacier is due to decadal fluctuation in air moisture and not man’s effects. The changes seen in the Swiss Alps likewise seem to have a greater natural, perhaps even dominant, variation than has recently been reported. Glaciers are highly sensitive to many environmental factors, most of which cannot be laid at the door of man-made climate change.