Beyond the media angles on the Himalaya paper
Looking at media coverage of a new Colorado University study on the contribution of ice loss to sea level rise, you’d be forgiven for feeling a little confused. While some reports focus on the extent of glacier ice loss, others lead on news that glaciers on the Himalayas aren’t losing ice. So what’s going on?
In brief, the paper suggests the world’s glaciers and ice caps contributed around 1.5 mm per year to global sea level rise between 2003 and 2010. This estimate is smaller than calculated in previous studies. In what was presented in the paper as a secondary finding, the researchers also found that high Asian glaciers in the Himalayas and surrounding areas don’t appear to be losing much if any ice, and are contributing a negligible amount to sea level rise.
The fact that the paper contains this point, in addition to the new estimate on sea level rise, has led to three types of story.
Most media outlets echoed the press release for the paper, which concentrates on the contribution of glacier melt to sea level rise. For example the Independent headlines with: Billions of tons of water lost from world’s glaciers, satellite reveals.
Second, there are stories that focus on the finding that the contribution of the world’s ice loss to sea level rise is less than previously calculated. For example, US News headlines with Earth’s Polar Ice Melting Less Than Thought; likewise the Telegraph with Melting glaciers on the Himalayas not contributing to sea level rise.
And third, other media outlets headline with the additional finding about the Himalayas – that high Asian mountains contribute a negligible amount to sea level rise. Take, for example, the Guardian article’s headline: The Himalayas and nearby peaks have lost no ice in past 10 years, study shows; or this from American Thinker: Mountains in Asia ‘lost no ice’ in last 10 years.
As Professor Jonathan Bamber, (a glaciologist at the University of Bristol not involved in the study), writes in an accompanying Nature News & Views article “Melting glaciers are an iconic symbol of climate change” – the fact that some are not melting so much as previously thought is big news.
Here’s a look at the whole paper and an summary of each of the findings.
Ice melt less than previously thought – but sea levels continue to rise
Nearly all of the ice on Earth is contained in the vast polar ice sheets covering Greenland and Antarctica. Yet scientists believe that, at present, ice loss from glaciers and ice caps outside the polar ice sheets contributes the most to rising sea level. These were the areas the researchers in this paper were particularly interested in measuring.
The researchers used satellite data measuring changes in gravity at the Earth’s surface to determine how much ice was being lost from glaciers and ice caps – ice masses covering less than 50,000 squared kilometres – all over the world.
The results, published in the journal Nature, show that ice loss from glaciers and ice caps contributed around 0.4 mm per year to sea rise between 2003 – 2010. This is a smaller estimate than previous attempts, which range from around 1.0 mm per year between 2001 – 2006 and 1.4 mm per year up to 2005.
Previous studies have suggested that ice loss from glaciers and ice caps has been the biggest contributor to sea level rise over the 20th Century, and is expected to remain an important factor in the 21st Century. Meanwhile, ice loss from the Greenland and Antarctic ice sheets is expected to take over as the dominant contributor to sea level rise over the 21st Century.
When the team included in their calculations the contribution to sea level from Antarctica and Greenland ice loss, they found that the combined effect of all the ice loss on sea level rise for 2003 – 2010 was also less than previous estimates. The findings do, however, still show that the world’s ice loss is contributing to sea level rise, which continues at an average of around 3 mm per year, as discussed in the following video:
The findings are important as this is the first study to use the same method for all of the world’s ice-covered areas. But more research is needed to understand the effect of ice loss on sea level, and to determine why there are differences between the observed and calculated sea level rise – Professor Bamber writes:
“Understanding, and closing, the sea-level budget (the relative contributions of mass and thermal expansion to ocean-volume change) is crucial for testing predictions of future sea-level rise. Estimates of the future response of GICs to climate change are, in general, based on what we know about how they have responded in the past. A better estimate of past behaviour, such as that obtained by [this study], will therefore result in better estimates of future behaviour.”
The Himalayan glaciers
It’s not surprising that several publications focused on the Himalayan glaciers.
After all, until this study, research suggested that the world’s glaciers have been retreating for the last few decades pretty much without exception. Himalayan glaciers were also the subject of some controversy when it came to light in 2009 that the Intergovernmental Panel on Climate Change’s 2007 report mistakenly stated that Himalayan glaciers would have melted away by 2035, rather than 2350 – an episode dubbed ‘glaciergate‘.
Bamber explains that the controversy over Himalayan glaciers:
“is not so surprising when one considers the problem in hand. There are more than 160,000 glaciers and ice caps worldwide. Fewer than 120 (0.075%) have had their mass balance (the sum of the annual mass gains and losses of the glacier or ice cap) directly measured, and for only 37 of these are there records extending beyond 30 years. Extrapolating this tiny sample of observations to all glaciers and ice caps is a challenging task that inevitably leads to large uncertainties.”
By using a uniform method that measures the whole of the Earth, this new study has overcome the need for these sorts of extrapolations.
Professor Jonathan Wahr, one of the paper’s co-authors from the University of Colorado Boulder, speculates why previous estimates of high Himalayan glacier melt might have been wrong:
“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.”
And this does not rule out high Himalayan glaciers melting in the future, as Professor Tad Pfeffer, another co-author of the paper from the University of Colorado Boulder explains:
“What is still not clear is how these rates of melt may increase and how rapidly glaciers may shrink in the coming decades, that makes it hard to project into the future.”
So what’s the take-home message from this research? Professor Wahr makes it very clear:
“Our results and those of everyone else show we are losing a huge amount of water into the oceans every year. People should be just as worried about the melting of the world’s ice as they were before.”