Opinion New scientific analysis of satellite gravity measurements has shown that ice is melting from glaciers around the world much less quickly than had been thought. The new research is important as worldwide glacier melt is thought to be one of the main factors which could drive rising sea levels in future.
The new results were derived by scientists including Professor John Wahr of Colorado uni. According to the new boffinry, glaciers and ice caps in places other than Antarctica and Greenland lost only 148 billion tons of ice each year from 2003 to 2010. This is some 30 per cent lower than had been previously estimated.
In particular, it appears that glaciers in the high Asian mountain ranges - the Himalayas, the Pamir and the Tien Shan - have been losing much less ice than was previously thought. Researchers visiting the region on the ground have previously suggested that the Asian mountain ice was depleting at rates as high as 50 billion tons per year, but Wahr and his colleagues' results show losses in the area of just 4 billion tonnes annually. They give the error in this figure as plus-or-minus 20 billion tons, so this much the same as saying that the Asian mountain ice - the planet's "third pole" - was unaffected.
“The GRACE [Gravity Recovery and Climate Experiment satellites] results in this region really were a surprise,” said Wahr, in tinned quotes accompanying publication of the new research. “One possible explanation is that previous estimates were based on measurements taken primarily from some of the lower, more accessible glaciers in Asia and were extrapolated to infer the behavior of higher glaciers. But unlike the lower glaciers, many of the high glaciers would still be too cold to lose mass even in the presence of atmospheric warming.”
It had been suggested by hard-green campaigners and journalists (regrettably endorsed by the UN Intergovernmental Panel on Climate Change) that the Himalayan glaciers might disappear by the year 2035, leading to imminent drought and starvation for billions, a claim since widely rubbished. The new GRACE readings would seem to be further confirmation of that prediction's foolishness.
Climate scientists remain deeply interested in melting ice in areas away from Antarctica and Greenland as it is one of the main factors in projected global sea level rise. According to the US Environmental Protection Agency and the IPCC, the main factors driving sea level rises now are: "the expansion of ocean water caused by warmer ocean temperatures, melting of mountain glaciers and small ice caps and (to a lesser extent) melting of the Greenland Ice Sheet and the Antarctic Ice Sheet".
Thus Professor Wahr's new results are highly important, and may require future projections of sea level rise to be revised.
“One big question is how sea level rise is going to change in this century,” says Wahr's Colorado colleague Professor Tad Pfeffer. “If we could understand the physics more completely and perfect numerical models to simulate all of the processes controlling sea level - especially glacier and ice sheet changes - we would have a much better means to make predictions. But we are not quite there yet.”
The new research is published in Nature.
Sea levels have risen globally at varying rates ever since the end of the last ice age. The rate of rise has only been measured at all consistently in the last two centuries, until recent decades entirely using tide gauges. Tide gauge measurements have, however, been seriously affected by various inaccuracies (not least the fact that the land the gauges are on rises and/or falls) and tide gauges have nowadays become much more complicated to compensate. As the sea level at any location rises and falls all the time due to tides, seasons, weather etc it is necessary to take readings over long periods to identify long-term trends.
The IPCC says that "no long-term acceleration of sea level has been identified using 20th-century data alone" but says that if limited 19th-century data is included then the rate of sea level rise can be shown to have started speeding up in 1870. However, recent research on tide-gauge readings indicates that the rate of rise is steady at the 20th-century rate of 1.7mm annually, or may even be decreasing slightly.
Since the early 1990s satellites have been used to monitor global sea levels. In contrast to tide gauges they have shown a steady, unchanged rate of rise of 3.2mm annually. This line is often added to the tide-gauge record up to 1990, showing a sharp upward curve.
If the rate of sea level rise remains steady at a few millimetres annually, there is probably no need to be much concerned about it: it would take centuries to rise by amounts comparable to the variations (tide, floods etc) which occur all the time anyway. If it accelerates massively as many climate scientists believe it will, sea level rise is probably the main reason to be concerned about climate change/global warming. ®