Daily Archives: 1 October 2012

Glacial pace

In 2007 the Intergovernmental Panel on Climate Change cautioned that “glaciers in the Himalaya are receding faster than in any other part of the world … and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high” (IPCC Fourth Assessment Report: Climate Change 2007, Working Group II: Impacts, Adaptation and Vulnerability, section 10.6.2).

But they retracted that claim quickly, because nobody could actually demonstrate they had any data to back it up. Few Himalayan glaciers were actually measured in the 20th century, and none were measured in the seven years prior to the statement being issued.

But a flurry of scientific research since then has shown a far more unpredictable situation than the generalisation that the Himalayan glaciers are melting.

Map of anomalies in the Earth's gravitational field, centred on south-east Asia, produced by the Gravity Recovery and Climate Experiment as a way of determining mass densities such as thickness of glacial ice (click to embiggen)
Map of anomalies in the Earth’s gravitational field, used to determine mass densities such as thickness of glacial ice. These maps are produced by the Gravity Recovery and Climate Experiment (GRACE), using two satellites nicknamed Tom and Jerry because they chase each other around the Earth. The satellites constantly track their separation distance, which changes when they pass over a gravitational anomaly (image by The University of Texas Center for Space Research and NASA)

The Himalaya mountain range is a vast geological formation stretching thousands of kilometres through Asia, from Bhutan in the east to Afghanistan in the west, and contains glaciers in multiple climates which are responding differently to rising air temperatures.

Those in the east are melting, but in recent years more than half of the glaciers further west near Pakistan have defied predictions by gaining mass. This is based not only on observations of the contraction or expansion of the leading edge of glaciers, but on satellite monitoring of glaciers measuring thickness of the ice.

Glacial ice is fed by annual precipitation from rain and snow and lost through melting in the warmer parts of the year. Current understanding is that increased rainfall in these areas has produced the increase in size of the glaciers, combined with low summer temperatures reducing the annual melt.

At the other end of the mountain range around Mt Everest, glaciers are thinning in Tibet and Nepal due to more ice melting from the glaciers each year than is being replaced. Many of these are fed by annual rainfall events like monsoons, rather than the year-round snow of some of the western glaciers, and reduced rainfall patterns could explain the continued weight loss.

Research has also found, probably not surprisingly, that dirty ice melts more slowly than clean ice, because rocks and other material on the surface provides a level of insulation against the warmer air.

Some of this analysis was only made possible by using recently declassified spy satellite photos shot in stereovision of the Russian and Chinese Himalayan borders dating back to 1959.

An estimate from 2010 predicted the Asian glaciers lost about 55 billion metric tonnes of ice annually. However, a pair of gravity measuring satellites nicknamed Tom and Jerry – from the Gravity Recovery and Climate Experiment – have indicated only a fraction of that figure at about 5 billion metric tonnes. That’s about the volume of 5,700 Empire state buildings.

One of the reasons such research is important is concern for freshwater supplies of countries fed by rivers originating in the mountains, such as the Ganges in India and the Yangtze in China. But calculations of the annual amount of water that flows into these rivers is that very little of the water comes from glacial sources, and the majority of flow in these epic rivers comes from more localised seasonal rainfall further downstream in the catchment.

The interaction of glaciers with climate and weather patterns are obviously dynamic, but the difficulties in measuring them can leave predictions about their future on thin ice.