Rising temperatures cause melting and retreat of large ice sheets, sea ice, and mountain glaciers – that’s pretty much common knowledge by now, as are implications on sea level, ecosystems, water supply and natural hazard risk. But a couple of news stories this week may cause confusion.
That the Greenland ice sheet is losing ice, and that mass loss has further accelerated in recent years, comes as no particular surprise. Using ground observations and satellite gravity measurements, a team led by Michiel van den Broeke from Utrecht University in the Netherlands, estimates that some 1,500 gigatonnes – roughly 1,500 cubic kilometers – have been lost from 2000-2008, equivalent to about 0.46 millimeters of global sea level rise.
Melting rates have accelerated since 2006, with mass loss reaching 273 gigatons of mass per year, equivalent to 0.75 millimeters of sea level rise. Without the moderating effects of increased snowfall, post 1996 mass losses would have been 100% higher, the team writes in a paper in this week’s issue of Science [subscription].
But the cryosphere – those parts of the globe that are permanently or seasonally covered by ice – does have surprises in store. Or so it seems.
Here’s one: Himalayan glaciers (there are tens of thousands of them of) are not – or at least not yet – shrinking as a result of climate change, the world learned this week from an Indian geologist.
“Although shrinking in volume and constantly showing a retreating front, [Himalayan glaciers] have not in any way exhibited, especially in recent years, an abnormal annual retreat,” concludes retired glaciologist Vijay Kumar Raina, formerly of the Geological Survey of India, in a report to India’s Ministry of Environment and Forests.
“It is premature to make a statement that glaciers in the Himalayas are retreating abnormally because of global warming,” he goes on.
Following the release of the study – based on observations of 25 glaciers – India’s environment minister Jairam Ramesh was quick to challenge the“conventional wisdom" about melting ice in the world’s tallest mountains.
Fellow Indian Rajendra Pachauri, the chairman of the Intergovernmental Panel on Climate Change (IPCC), was put out: “We have a very clear idea of what is happening. I don’t know why the minister is supporting this unsubstantiated research. It is an extremely arrogant statement,” he told the Guardian.
The IPCC had warned in its latest report, published in 2007, that Himalayan glaciers “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 if the Earth keeps warming at the current rate.”
So what’s going on? I asked Lonnie Thompson, a veteran glaciologist and leading paleoclimatologist at Ohio State University. Here’s what he said:
“First and foremost this is not a peer reviewed report and nothing scientific can be claimed based on 25 glaciers out of over 15,000 glaciers in the Himalayas and 46,300 in the Himalayas and Tibetan region.”
“Glaciers response time to climate change depends on their size; larger glaciers take longer to heat up and respond than smaller glaciers. Thus, in a mountain range such as the Himalayas with over 15,000 glaciers some will be stationary or advancing based on what climate change happened over 100 years ago. Some glaciers are surging glaciers that advance and retreat due to dynamics of ice flow and not climate. Glaciers do respond on the short term to increases in precipitation as well as temperature but with time temperature will win.”
“At the end of the day we have to go with the balance of evidence and that is true for glaciers as well. In short, if Jairam Ramesh can write up these results showing just how he came to his conclusion for a quality peer reviewed journal then he should do so.
“Otherwise the report certainly does not challenge the conventional wisdom. I certainly concur with Ramesh that it is high time that the government of India makes investments in the study of the glaciers in the Himalaya’s as they will certainly be impacted by their loss.”