In the aftermath of Glaciergate, this week's issue of the journal Science includes a sober and informative review article by a large team of researchers lead by Tobias Bolch of the University of Zurich on the state and fate of Himalayan glaciers. Unfortunately, the paper is pay-walled. I think this is a another nice example of an article that should be unlocked to show that technical and objective, and at the same time accessible and also quite relevant, information in climate research is still possible.
The article contains a wealth of information about the evolution of Himalayan glaciers since the mid 19th century and estimations of their possible fate in the future. I will only highlight the points that called my attention, although probably there are many others that may be more important for glaciologist. The article makes quite clear that not all Himalayan glaciers behave in a similar manner: the Karakoram seems to be somewhat special and decoupled from the general evolution of the rest of Himalayan glaciers. A bit surprising is that the Karakoram glaciers are currently gaining mass, whereas for the rest of glaciers the mass balance is negative. This underlines the complex response of glaciers to climate forcing. It is well known that the mass balance of some glaciers are more strongly driven by precipitation than by temperature. During the Little Ice Age , for instance, some Norwegian glaciers gained mass, whereas other glaciers from surrounding regions lost mass, probably reflecting a shift in the weather patterns that brought moisture to those glaciers.
With a longer term perspective, most Himalayan glaciers have been loosing mass since the mid 19th century, but there are exceptions to this general tendency. Again, the Karakoram arises as a special region. The glaciers here apparently show a quite heterogeneous behaviour but in general they have been quite stable or slightly increasing also on this long time scales. Another exception for all Himalayan glaciers is that this long-term tendency towards mass loss was interrupted during 1920-1940 where ' about half other records show stationary or advancing tongues'. I was quite surprised to read this sentence here, since as it is well know, those 3 decades were characterized by strongly rising global mean temperature that culminated around 1940. Maybe the in-situ temperature evolution during 1920-1940 was different from the global mean - I guess that the local records from this region are not very trustworthy also considering its complex topography. Nevertheless, it reminded me that the relationship between global mean temperature and glacier melt and this also to global sea-level, can be far more complex that one may think.
Another interesting result is that the mass loss of the Himalayan glaciers except Karakoram started already in the mid 19th century. The figures provided in the article do not allow to discern a clear acceleration in the mass loss in the recent decades. There are some hints that the mass loss is now a bit higher than at the turn of the 20th century, but it does not look very dramatic. The renowned expert in world glaciers, Johannes Oerlemans, who also authored a reconstruction of the Northern Hemisphere mean temperature based on historical glacier records, has indicated in several talks I have witnessed that glacier retreat started before anthropogenic greenhouse gas forcing could have been important.
Now to the sentence you all are probably awaiting :
The statement that most H-K [ Himalaya-Karakoram ] glaciers will likely disappear by 2035 is wrong (8), as shown by simple but physically robust modeling (50). More realistic projections (5), relying on degree-day modeling but reporting the H-K glaciers only as part of High Mountain Asia, are consistent with the simpler model in suggesting moderate mass loss over the 21st century
Yes, the IPCC
TAR AR4 was wrong regarding the Himalayan glaciers and apparently it was easy to show that it was wrong. All in all, in my view this was an important error in the Third Fourth IPCC Report. Theoretically, the governments of the countries surrounding the Himalayas would have been severely affected by a disappearance of Himalayan glaciers as soon as 2035, so that they should have immediately started to design a contingency plans. Well, nobody did anything of that sort, probably because they actually did not believe those IPCC projections anyway. This error in the Third Fourth IPCC report tells more about the real influence (credibility among policy makers?) of the IPCC than about the science itself.
This being said, the paper continues:
Nevertheless, all models project mass losses in coming decades that are substantial for most parts of the Himalayas, but consistently fall well short of complete region- wide glacier disappearance even by 2100
This result sounds logical. With increasing temperatures, glaciers in general will tend to shrink. However, given the demonstrated complex behaviour of these glaciers, I would have liked to see a glacier simulation over the 20th century, preferably driven by a regional climate model, that could explain why the Karakoram glaciers are special.