文章 Articles

Global warming and Chinese glacier melting

Glaciers continue to retreat from the roof of the world, writes Stephan Harrison. Now dust storms, permafrost melting and water scarcity loom as damaging environmental consequences of global warming on the Tibetan plateau.
Article image

The mountain ranges of the Tibetan plateau contain the largest concentration of glacier ice outside of the high latitudes, yet, until quite recently, large areas were relatively unknown to western scientists. In the last couple of years, a number of scientific reports written by Chinese glaciologists have provided inventories of the mountain glaciers of Tibet and assessed their response to recent climate change. These findings make uncomfortable reading. 

The Tibetan plateau is bounded by enormous mountain ranges -- to the south by the Himalayas, to the north by the Tian Shan and to the west by the Karakoram and Pamirs -- and is the size of western Europe, forming the largest high-altitude land mass on earth. At an average height of around 4,000 meters above sea level, the plateau contains more than 45,000 individual glaciers covering about 90,000 square kilometers and extensive permafrost. 

Recent work by Dong Guangrong at the Chinese Academy of Sciences has shown that recent climate change has had a severe impact on the mountain glaciers and permafrost of Tibet and threatens to affect water supplies to many of the rivers draining the plateau. His analysis of data from 680 Chinese weather stations shows that average temperatures in Tibet have risen 0.9° centigrade since the 1980s and this has precipitated an annual 7% reduction in glacier extent and the melting of permafrost. These findings provide further support to research published in 2005 by American scientists who observed significant recent warming in Tibet from ground-based surveys.

These observations are in line with those from other regions of the earth and there is now a general consensus among climate scientists that the planet is undergoing significant warming, mainly as a result of human-induced emissions of greenhouse gases and land-use changes. The last Intergovernmental Panel on Climate Change Third Assessment Report (IPCC TAR) was published in 2001, and showed that global mean surface temperatures had risen some 0.6 centrigrade since the beginning of the 20th century. While to many this temperature rise does not seem significant, palaeoclimatological studies suggest that this means that the earth is warmer than it has been for at least the last 1,000 years (NAS 2006) and there is compelling evidence from glaciers to suggest that the planet is warmer now than it has been for 5,000 years. In addition, warming is occurring at a faster rate than for the last 10,000 years. The consequences of this temperature rise have been well documented, but include rapid recession of mountain glaciers, rising sea levels, changing patterns and intensities of rainfall and drought events and latitudinal shifts in ecological systems. Projections of future temperature rise during this century using computer models range from around 2 to 6 degrees centigrade; projections from assessment of past climate sensitivity suggest that warming could be even higher. The implications of such change for ecological, economic and political systems would be enormous.

There are also clear societal implications of climate change. Globally, around 1.7 billion people live in arid regions with restricted drinking water and this number is expected to rise to 5 billion within the next 25 years. Similar findings from similar studies from other parts of the world reinforce the message that climate change is global in extent and that warming is not an artefact of urban heat islands. Two things make the Chinese study unusual, however. First, glacier recession and permafrost degradation in Tibet is inextricably linked to changes in water supply and dust storms, and, second the extent of the changes to the Tibetan environment may have global climatic significance.


Photo by Hu Miao

Glacier recession and water supply

Water supply increases during the period of glacier recession and the period of time when flow is high is extended as the ablation (melting) season extends. This period may be short-lived, as once the glacier has melted (or has become covered with debris), runoff is greatly reduced and will eventually depend upon more seasonal precipitation, changing the variability of river discharge, with consequent impacts upon agricultural systems downstream.

Glacier recession has other implications for water supply. As glaciers melt and lose mass, surrounding hillsides become unstable, producing debris flows and rock slides which deliver large amounts of sediments into the valley bottoms. This increases the sediment load of rivers, which adversely affects hydro-electric power schemes downstream and reduces the economic life of reservoirs and irrigation schemes. 

In China, recession of the mountain glaciers threatens to disrupt the water supply of over 300 million people as many of the great rivers of the Asian continent (Yellow, Mekong, Indus, Ganges and others) have their headwaters on the Tibetan plateau, and in over 100 cities in China, including Beijing, the water situation is critical. As is the case with other arid Asian countries, climate change, water supply, and social and economic stability are inextricably linked.

Dust storms

Deserts in China are related largely to the position and nature of the east-Asian and Indian summer monsoons, which control rainfall. They are located in the arid centre of the country, away from oceanic influences and protected by the mountains to the west and south from incursion of rain-bearing winds. During the winter, they are affected by the Siberian high-pressure system bringing dry and very cold conditions. Climate change, allied to unsustainable land-use practices, is increasing the number and size of dust storms from these deserts. A report in 2001 showed that 2,300 square kilometers of topsoil is lost to dust storms each year from northern China alone. This year, northern China experienced 13 major dust storms, one of which deposited over 330,000 tons of sand in Beijing in April and others have deposited dust in Russia, South Korea and the central United States. 

Permafrost melting

Dust storms are also associated with thawing of previously frozen soils and, with much of the Tibetan plateau underlain by permafrost, climate change threatens to increase the scale of desertification in the region. Of wider concern is the likely positive feedback to global warming caused by the release of greenhouse gases such as methane and carbon dioxide from frozen soils as they thaw.

Recent studies have shown that methane will be released if melting permafrost produces waterlogged soils, and carbon dioxide if the soils dry out. With estimates of the amount of carbon locked up in permafrost ranging between 60 and 190 billion tons, thawing of the soil over vast tracts of the Tibetan plateau will produce an enormous release of greenhouse gases to the atmosphere and a likely further step-change in global warming, with severe consequences for us all.

Studies such as these demonstrate how interconnected the climate system is; emissions of greenhouse gases in one part of the world impact upon glaciers and permafrost in another, which in turn result in further emissions. The melting of glaciers in China is not only of concern to the Chinese.

 

The Author: Stephan Harrison is a geomorphologist, specialising in landscape responses to climate change, at Exeter University and Oxford University. He has worked in the mountains of central Asia, Patagonia, central Europe and northern Scandinavia on climate change issues.

Now more than ever…

chinadialogue is at the heart of the battle for truth on climate change and its challenges at this critical time.

Our readers are valued by us and now, for the first time, we are asking for your support to help maintain the rigorous, honest reporting and analysis on climate change that you value in a 'post-truth' era.

Support chinadialogue

发表评论 Post a comment

评论通过管理员审核后翻译成中文或英文。 最大字符 1200。

Comments are translated into either Chinese or English after being moderated. Maximum characters 1200.

评论 comments

Default avatar
匿名 | Anonymous

水资源管理的又一大障碍

这篇文章对人口稠密的亚洲大陆未来的水资源管理敲醒了警钟。(一个令人惊讶的统计:全球人口的47%所居住的河流分水岭都流经或起源于中国)。但是有一点是众多研究评论都没有提到的,那就是冰川融化是否真的会在短期内增加起源于青藏高原的河流的水流量。如果真是这样的话,那么政府试图通过改善水资源管理(譬如有效政策,规章制度,以及水价调整)以提高水资源有效使用率和减少水消耗量的努力将会遇到障碍。John Warburton

A disincentive for better water management?

This article provides many alarming warnings for the future of water resources in the densely populated Asian continent. (An amazing statistic is that approx. 47% of the global population lives within the overall watersheds of rivers that flow within or arise in China). But one issue that the various studies cited do not seem to have addressed is whether glacial melt will actually lead, in the short term, to increased volumes of water in the great rivers that arise in the Tibetan Plateau. If this were the case, it could unfortunately be a disincentive for governments to tackle the urgent need to improve water use efficiency and reduce water consumption, through better management of water demand (through appropriate policies, regulations, and pricing etc.). John Warburton

Default avatar
匿名 | Anonymous

水资源管理的又一大障碍

John. 谢谢你的评论。我也认同在短期内水供应不足问题会因此得到缓解。希望政府组织作出决策时能征求科学家的意见,并对这篇文章引起重视。Stephan Harrison

A disincentive for better water management

John. Thanks for your comment. Yes, I agree that in the short term water supply problems may be mitigated by increased runoff. Hopefully the political organisations involved in decision-making are talking to the scientists and are aware of this issue.
Stephan Harrison

Default avatar
匿名 | Anonymous

全球变暖

今年全球极端事件会议焦点聚集在气候效应的范围逐渐扩大和影响在加剧。

全球变暖国际评审委员会主席沈星扬教授领导着全球极端事件与紧急反应的研究和努力。

长远来说,气候变化将造成很多气候模式的改变,而接着地球将转向另一个平衡的阶段。

在不久的将来,气候变化将招致恶劣天气和极端事件的发生。

Global warming

The focus of this year's conference is Global Extreme Events, characterized as large-scale climatic effects that have been increasing in magnitude and frequency. Prof. Sinyan Shen, Chairman of the GW International Program Committee, has been leading the world on Global Extreme Events and Emergency Response. In the long term climate change will cause the Earth to transit to another equilibrium state through many oscillations in climatic pattern. Global warming causes extreme events and bad weather in the near term.

Default avatar
匿名 | Anonymous

全球变暖

今年全球极端事件会议焦点聚集在气候效应的范围逐渐扩大和影响在加剧。

全球变暖国际评审委员会主席沈星扬教授领导着全球极端事件与紧急反应的研究和努力。

长远来说,气候变化将造成很多气候模式的改变,而接着地球将转向另一个平衡的阶段。

在不久的将来,气候变化将招致恶劣天气和极端事件的发生。

Global warming

The focus of this year's conference is Global Extreme Events, characterized as large-scale climatic effects that have been increasing in magnitude and frequency. Prof. Sinyan Shen, Chairman of the GW International Program Committee, has been leading the world on Global Extreme Events and Emergency Response. In the long term climate change will cause the Earth to transit to another equilibrium state through many oscillations in climatic pattern. Global warming causes extreme events and bad weather in the near term.