GRACE and Glacial Ice Melt
February 13, 2012
Potholer is johnny-debunker-on-the-spot once again, with this most recent video on last week’s blaring headlines – you may have seen them – “The Himalaya Glaciers aren’t melting so there is no global warming”.
The basic story is that we have a new paper in Nature with recent results from the GRACE satellite, which gives measurements on mass gain and loss, especially for areas of ocean and ice. The study basically confirms large ice loss globally over the previous 8 years, which have been contributing to sea level rise – but raises some questions about whether ice in the highest Himalayas is melting as rapidly as previous surveys have suggested.
As Potholer shows, whatever the disposition of the Himalayan area, the Fox news headlines are, as always, false and misleading.
As in all scientific inquiry, one paper is never the complete and final picture.
Dr. Mauri Pelto, an advisor to this series, and director of the North Cascade Glacier Climate Project, expresses some doubts about the current Nature paper:
“This result is certainly not correct. A quick glance at the results suggests problems in the region with GRACE, and the fact that the results do not jive with the detailed inventories that have looked at 1000′s of glaciers and their areal losses. I cannot tell you why GRACE was not accurate in the Himalaya, though we will find out in time.”
“GRACE has demonstrated itself to be quite sensitive to glacier and ice sheet mass change and has been validated in several regions. The recent paper is an ambitious step assessing all of the worlds ice covered areas. GRACE has problems with small glaciers and has not been validated in such areas.”
“The results from the Himalaya do not appear robust, when compared to the very extensive inventories that have documented the changes in extent of thousands of glaciers in the region and have found significant changes in areal extent across all ranges except the Karakoram. The glacier by glacier mapping completed by GLIMS or ICIMOD for example tell a different and better verified story, from Kyrgyzstan to Bhutan and Afghanistan”
Below is an interview with Dr. Pelto that I conducted last August, and his recent blog posting on mass balance of Himalayan Glaciers, reposted with permission.
Samudra Tupa Glacier Retreat and Himalaya glacier mass losses
In a glacier inventory in the basin by Kulkarni et al (2007) the 466 glaciers in the basin were observed to have lost 21% of their total area from 1962 to 2001. This program coordinated by the Space Applications Centre of the Indian Space Research Organization, has combined field observations of the glacier with remote sensing to observe the changes in area and length of the glaciers, immediately below is a 2006 picture of the glacier terminus and proglacial lake from Kulkarni.
The terminus ends in an expanding proglacial lake. The lower glacier is heavily debris covered, has a low slope and is essentially stagnant. These factors will lead to continued retreat. In this post we use 1998, 2002 and 2011 Landsat imagery to examine the terminus of this glacier. The glacier terminates at 4225 meters, the snowline in 1998 is 5200 meters and 2002 is 5300 meters, neither of the images is at the end of the ablation season. An ELA ( Equilibrium Line Altitude - the point at which accumulation equals melting) of 5200-5300 meters leaves an accumulation area insufficient to maintain the current glacier size. In 1970 the ELA was at 4900 meters Kulkarni et al (2007) .
A close up view of the termini of Samudra Tupa-pink arrow and a nearby unnamed glacier-green arrow indicate the changes in 1998, 2002 and 2011 in that order. The green arrow points not to the terminus but to a prominent knob near the end of the glacier in each image, it is the control point. The last two images illustrate the changes from 2002 to 2011 in an image overlay. The last image is the 2011 termini of Samudra Tupa Glacier from Kulkarni, 2009.
The retreat is noted by Kulkarni, 2009 as 13 meters/year during the study period. From 2002 to 2011 the glacier retreated nearly 200 m, closer to 20 meters/year. The retreat of this glacier is less than that of other large glaciers nearby Sara Umaga and Gangotri. The loss in glaciated area in the basin of 21% is also similar to other areas in the Altai, Himalaya, and Pamir.