 |
| Pindari Glacier - Wikipedia |
Local Warming - the Himalayas
Why worry about the Himalayan glaciers? There are no glaciers in Scotland but the mountains feed the rivers with copious water all the year round. Should we be specially concerned about the effects of global climate change on the Himalayas?
The Himalaya is a vast area. It contains 12000 glaciers that occupy 33000 square kilometres. In the West of the Himalayas the glaciers act like Alpine glaciers, they store ice in the winter and release water into rivers in the summer and this dominates the flow of the Indus in the summer. In the East (East of the Chenab basin) glacial melting is less important and it is precipitation, especially the summer monsoon, that drives river flows. The Ganges is fed from this Eastern catchment. There is also a third type of catchment in the Ladakh region where there is little precipitation and rivers are fed from melting permafrost and glaciers.
The Western Himalayas - the Indus Catchment
In the summer the Indus is fed by glacial runoff and melt. If these glaciers disappeared there would be a risk of the Indus becoming a seasonal river. The growth and retreat of glaciers depends upon the amount of melting, the quantity of snow falling and the height of the snow line. In general the glaciers equilibrate so that they lie just above the snow line (Osterm 1973). At present the glaciers of the Hindu Kush and Karakoram, which feed the Indus, lie above the mean annual snow line and are increasing in extent (Fowler and Archer 2005, Hewitt (2005)). The Karakoram glaciers studied by Fowler and Archer lie at 5,000-6,000 m and the current snow line is 3500-4500 m. It looks like the snow line would need to shift by 1500 m for direct melting due to warming to have a serious effect on these glaciers. In the part of the Himalaya studied by Kulkarni the snow line shifted about 200m for each degree rise in mean regional temperature so it would take an incredibly unlikely seven degree rise in temperature to bring these Karakorum glaciers below the snow line.
The Eastern Himalayas - the Ganges Catchment
The effect of the glaciers on the Ganges is not as straightforward as it might appear. Thayyen. R.J. and Gergan, J.T. (2009) have reviewed the hydrology of a part of the area and measured the contribution of various parts of a large Himalayan catchment area to water flow in rivers over the period 1998 to 2004. They point out that in the this part of the Himalayas there are winter rains and snows and Summer Monsoons falling as snow and rain. This means that to some extent the Himalayas act as a normal, non-glaciated river catchment area. Even the run-off from the glacier mouth is due to a mixture of precipitation, snow-melt and glacier melting:
"the melting of glacier ice contributed 4.83×106 to 5.17×106 m3 during 1994–2000 periods (Dobhal et al., 2007), which constituted 7.7 to 12.7% of the bulk glacier runoff"
As might be expected, the glacial runoff has the greatest effect on river flow in summers with poor precipitation, contributing up to 74% of the summer flow in 2004, which had low precipitation compared with 47% of summer flow in 1998 which had strong precipitation. However, this glacial runoff was largely due to snow melting in the glaciated part of the catchment. The upshot of this work seems to be that the glaciers may provide a water reservoir for summers that have low precipitation. The reservoir is largely in the form of the snow that accumulates around the glaciers. The size of this snow reservoir is possibly affected by the cold local micro-climate of glaciated valleys, the cold causing increased precipitation of rain and snow.
These measurements mean it is possible that the absence of glaciers could reduce the summer reservoir in dry summers by about 15-20% if the valleys acted like non-glaciated valleys once the glaciers were removed (basis of estimate: in a dry year 74% of annual flow due to glacial runoff, 10% of this is glacial melt so melt produces 7.5% of annual flow, but at least twice this for the summer only). Sadly this prediction contains a big "if". It is possible that factors such as altitude would enable an enhanced reservoir effect compared with currently non-glaciated catchment areas despite the loss of the ice. However, it is even more probable that the loss of the glaciers would lead to a hotter local climate that would reduce the summer reservoir in glaciated and non-glaciated valleys alike and so a 50% or more reduction in dry summer flow could be conceivable. We need a "guesstimate" of the effect of de-glaciation on dry summer river flows: my hunch is to go with the measurements and suggest a reduction of summer flow in dry summers by around 20% if the glaciers all melted and all other factors were constant and a reduction in reservoir capacity by 50% or more if significant local warming occurred once the glaciers were gone.
The disappearance of the glaciers in the Ganges Catchment would have a devastating effect during a failed monsoon. Even a 20% decrease in river flow is highly damaging during a drought in an area that depends on irrigation, a 50% decrease would be catastrophic.
But would global warming or local warming cause the glaciers to disappear? The main effect of generalised warming is to move the "snow line", the level at which precipitation falls as snow, further up the mountains. This has a dramatic effect on glaciers because not only are they deprived of snow but the rain that falls elow a snow line melts ice. The snow line in the Ganges Catchment has changed by 400 metres between 1980 and 2008 (See Indian space research organisation slides by Kulkarni). Moving from around 4800 metres to 5200 metres. As confirmation of this, in the study by Thayyen. R.J. and Gergan, J.T. (2009) described above the glaciers in the catchment were at about 4700 metres. These glaciers have now fragmented (Kulkarni et al 2007) as the snow line rose.
There is considerable photographic evidence of glacier retreat:
Right click the photo to toggle to full screen.
Other photos: [PDF] Complex and shifting Himalayan glacier changes ..
There are also some scientific studies available for online perusal. For instance Shuklal et al (2008) produced a detailed study of the Samudratapu glacier, Chenab basin, Himalayas between 1976 and 2004 and found it to be retreating at 27m per annum. NASA studies of images the Gangotri glacier show a similar trend, see Retreat of Gangotri (NASA Earth Observatory http://earthobservatory.nasa.gov ). Kulkarni et al (2007) cover the changes in the Ganges catchment.
The evidence shows that there has been a rise in the snow line in the Himalayas due to warming and this has led to melting of glaciers. If the glaciers melt entirely there will be a risk of catastrophic drought in the Ganges basin if there is a weak summer monsoon.
The rate of future retreat of the glaciers depends on several factors such as the rise in the snow line, the fragmentation rate of the glaciers and the amount of snow falling. Kulkarni et al (2005) have predicted that the Parbatti glacier will lose about 10% of its length by 2022. If current trends continue the rate of retreat will accelerate because of fragmentation of large glaciers into many smaller, rapidly melting glaciers. The snow line is perilously close to the eastern glaciers so their future is uncertain, at current rates of snowline rise (approx 100 m per decade) many of the eastern glaciers will be below the snowline in only 40 years.
Summary of Western and Eastern Himalaya data
The glaciers in the East are melting, those of the Karakorum are not. The Indus is probably secure for the foreseeable future but the Ganges basin may be at considerable risk during droughts if the eastern glaciers melt. The eastern glaciers might melt away within 40 years if current trends of fragmentation and rising snow line continue.
Climate skeptics versus eco-warriors
The eco-warriors got egg on their faces with a series of reports that the Himalayan glaciers would all be gone in 35 years. This does not look credible on the basis of the data (the Western Himalayas will be OK) and seems to have been a mistake reported in New Scientist that was propagated even into the IPCC report!
The varied nature of the changes in the Himalaya have led to a lot of confusion that has been exploited by the skeptics. A good example is the Infowars article where the growth in glaciers in the West is used to "show" that glaciers are not retreating at all in the Himalayas. This erroneus article is used in various other skeptical sites (Globalwarminghoax.com).
See also:
The Evidence for Global Warming. (2) Analysis using source data for global changesGlobal warming (3) man or nature?
The strange case of the missing CO2
Global Warming: What Will Change?
Is climate change a threat because of overpopulation?
Blue Haze, Brown Clouds and the need to stop Geoengineering before it begins.
Global warming: what do we do now?
References and further reading
Fowler, H.J. and Archer, D.R. (2006) Conflicting Signals of Climatic Change in the Upper Indus Basin. Journal of Climate 2006 19(17) pp. 4276–4293
http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2FJCLI3860.1
Hewitt, K. (2005) The Karakoram Anomaly? Glacier Expansion and the 'Elevation Effect,' Karakoram Himalaya. Mountain Research and Development. Vol 25. (4):332-340
Kulkarni A. Slideshow http://www.slideshare.net/equitywatch/kulkarni-glacier-august27-revised
Kulkarni et al Current Science 88(11) 2005
Kulkarni et al (2007) Glacial retreat in Himalaya using Indian Remote Sensing satellite data
CURRENT SCIENCE, VOL. 92, NO. 1, 10 JANUARY 2007. http://www.ias.ac.in/currsci/jan102007/69.pdf
Osterm, G. (1973) The Transient Snowline and Glacier Mass Balance in Southern British Columbia and Alberta, Canada. Swedish Society for Anthropology and Geography. Geografiska Annhaler 1973 2 p. 93. http://www.jstor.org/pss/520877
,
Shuklal, A., Guptal, R.P. and Arora, M.K. (2008). Remote Sensing based Study of Retreat of and Accompanying Increase in Supra-glacial Moraine Cover over a Himalayan Glacier
A Shukla1, RP Gupta1 and MK Arora2 EXTENDED ABSTRACTS: 23RD HIMALAYAN-KARAKORAM-TIBET WORKSHOP 2008, INDIA
,
Thayyen. R.J. and Gergan, J.T. (2009). Role of glaciers in watershed hydrology: “Himalayan catchment” The Cryosphere Discuss., 3, 443–476, 2009 www.the-cryosphere-discuss.net/3/443/2009/
perspective http://www.the-cryosphere-discuss.net/3/443/2009/tcd-3-443-2009-print.pdf
World Wildlife Fund An Overview of Glaciers, Glacier Retreat, and Subsequent Impacts in Nepal, India and China http://www.panda.org/downloads/climate_change/himalayaglaciersreport2005.pdf and http://assets.panda.org/downloads/glacierssummary.pdf
http://www.earthtimes.org/articles/show/297875,satellite-images-show-himalayan-glacier-receded-15-km-in-30-years.html
http://timesofindia.indiatimes.com/home/environment/global-warming/Melting-Himalayan-glaciers-threaten-13-billion-Asians-/articleshow/5306753.cms
14/1/2010
Comments