A paper published last year in the Indian journal Current Science (pdf) has recently been raised in the Indian parliament. A number of scientists have been rightfully critical of this paper in different online forums. In this post, I’m going to take a quick look at the results of the paper, which are surprising to anyone familiar with the current state of Himalayan glaciology.
Why are the results surprising? Based on a sample of 2018 glaciers, the paper’s authors suggest that nearly 87% of the glaciers in the region have stable snouts, while 12% have retreating termini, and < 1% are advancing.
There are a number of issues with these figures, which lead the authors to the incorrect conclusion that glaciers in the region are actually in steady state. In no particular order, these issues are:
- Glacier snout position is determined by a complex range of factors, including climate, dynamics, and lag times. Over short periods (i.e. less than 10 years, as in this paper) the behaviour of the terminus may not be indicative of the overall health of a glacier.
- Glacier retreat is a very different thing from glacier mass loss. Glaciers lose mass primarily due to downwasting (surface lowering), not terminus retreat. And study after study has confirmed that glaciers across the region (except for the Karakoram) are losing mass.
- The position of the terminus on debris-covered glaciers can be difficult to interpret, and it will not respond to climate change in the same way as the terminus on clean (debris-free) glaciers. The authors do not distinguish between debris-covered and clean glaciers in their terminus assessments.
- Its not clear how the 2018 glaciers were sampled. There are over 54,000 glaciers in the HKH region, and while a 3% sample size is not too bad, biased sampling for debris-covered or large glaciers make extrapolations to the entire population problematic.
Finally, the “stable” glacier examples given in the paper actually show glaciers in retreat! Here is a Landsat pair (data available at www.earthexplorer.usgs.gov) from 2001 and 2014 for the Gangotri Glacier, in the Garwhal Himalaya (Figure 7 in the Current Science paper):
Not only is the Gangotri (the main north-flowing glacier in the center of the image) in retreat, but you can also literally see the downwasting occur as the distance between the active ice surface and the large lateral moraines gets bigger. Smaller glaciers throughout the region also appear to be in retreat.
The authors also use the example of Siachen Glacier in the Karakoram Range (Figure 8 in the Current Science paper). This is the terminus of a massive glacier system (ca. 700 km²) and the Landsat pairs I pulled from 2000 and 2013 also appear to show retreat and deflation at the terminus:
Bottom line: the Current Science paper is simply not credible. The conclusion that > 80% of glaciers in the region are stable is based on incorrect interpretations of satellite imagery, a possibly biased sampling method, and an unjustified reliance on short-term changes in terminus position as an indicator of glacier health.