Temps de lecture :3 minutes
The scientists whose research has revealed the extent of global climate change are now getting the tabloid treatment. First came the scandal of leaked (actually hacked) e-mails at the climate institute of Britain’s East Anglia University. Now comes the supposed news that the Himalayan glaciers are not, in fact, retreating, and will therefore not disappear by 2035.
The first story was timed to appear just before December’s COP15 climate-change summit in Copenhagen. The second is designed to bury whatever hopes still exist for signing a successor treaty to the Kyoto Protocol. Coming one after the other, these inflated scandals have, at least for now, dealt a massive blow to the credibility of the evidence that underpins the battle against global warming.
But how justified are these attacks, particularly the attacks on the Intergovernmental Panel on Climate Change, the United Nations body that has set the gold standard for analyzing global climate change? One tell-tale sign is the climate skeptics’ contempt for the actual data in the Indian government’s study, which is being used to undermine the IPCC report and the impeccable credentials of the scientist Syed Iqbal Hasnain, the source of the IPCC’s alarming quote on the Himalayas. There is also the unholy glee with which they have set about destroying an icon of the anti-global warming movement, the Nobel Laureate R.K Pachauri, by attributing financial motives to his research.
Hasnain, who is currently conducting a study of the accumulation of black carbon on snow at high altitudes in the Himalayas, is not some egotistical scientist seeking the limelight. He was Professor of Glaciology at Jawaharlal Nehru University’s School of Environmental Sciences and a fellow of the Indian Institute of Technology and of Delft Technical University in the Netherlands. Between 1995 and 1999, he chaired a working group on Himalayan Glaciology within the International Commission on Snow and Ice. He is also the author of Himalayan Glaciers: Hydrology and Hydrochemistry and scores of scientific papers.
Hasnain made his remark to the New Scientist in 1999, only five years after the retreat had reached its peak and only two to three years after the slowdown began – far too soon to say that the trend had changed. The IPCC’s use of his remark may have been rash, but was not misleading because in 2003-2004, the year before it finalized its fourth report, the changed trend would have been barely perceptible
What the 2009 report for the Indian Ministry of Forests and Environment actually says is that the average retreat of glaciers, approximately five meters per year since the 1840’s, when records began to be kept, accelerated sharply between the 1950’s and 1990’s. But the retreat slowed after the mid-1990’s until, for some of the biggest and best-known glaciers, such as Gangotri and Siachen, it had “practically come to a standstill during the period 2007-2009.”
But, the retreat of a glacier’s “snout” is only one of three measures of how glaciers can change. The other two are its “mass balance” and the rate at which melt-water is discharged. The Himalayan glaciers have not stopped losing mass, although they are losing it at a somewhat slower rate than before. Evidence collected on 466 glaciers by the Indian Space Applications Center from 1962 to 2004 shows a 21% loss of glacier area and a 30.8% of glacier volume.
The same study also shows that smaller glaciers are shrinking much more rapidly than larger ones. While glaciers that cover more than five square kilometers have lost 12% of their mass, those under one square kilometer have lost 38 percent. Applying the overall ratio of mass lost to area covered, this means that the smallest (and most numerous) Himalayan glaciers lost up to 57% of their mass between 1960 and 2004.
What could have caused the glacier snouts to have stopped retreating? One factor could be deposits of dust and black carbon (collectively called aerosols) upon the snow, which, up to an accumulation of 400 grams per square meter sharply raises the rate of melting. Between 400 and 600 grams, it has no further effect, but when it exceeds 600 grams, it acts as a shield against the sun, and slows down melting.
Much thicker coatings of aerosols at the lower ends of glaciers might explain the tendency in several glaciers, noted in the Indian report, to become narrower in the middle, forming two distinct parts. The slowdown in the retreat of the snout of glaciers could, therefore, be a consequence of the very rapid rise of human population in the hills and desertification caused by overgrazing – purely local factors that boost aerosol levels.
Only more research focused on the differences between glaciers in heavily populated areas and those in uninhabited ones like Siachen will answer this question definitively. But relying upon population growth and desertification to prolong their lives would be robbing Peter to pay Paul.
What needs to be explored is not the validity of the secular trend, but the nature of the local influences working against it. By rushing to apologize for a statement they clearly did not understand, British Secretary for Energy and Climate Change Ed Miliband and others have impugned not only the honesty of scientists like Hasnain, but also the credibility of science itself.