Asian glaciers on the Tibetan Plateau also controlled by west winds over Europe
Publication in Nature Climate Change
The Tibetan Plateau and its adjacent mountain ranges, for example the Himalaya, have become a focus of climate research in recent years. On the one hand, the plateau plays a significant role in the formation of the Asian monsoon, which influences more than a billion people by annually recurring monsoonal rains. On the other hand, glacier mass loss in High Asia impacts the regional water balance and natural hazards, and contributes to sea-level rise. In light of this significance, and considering the two large ice sheets, Greenland and Antarctica, the large-scale Asian mountain system has also been called the "third pole".
So far, researchers assumed that glaciers outside the northwest of the mountain system (e.g., Karakoram and Pamir) are controlled by the activity of the tropical monsoon. However, the new study shows that this assumption is incomplete, based on a glacier on the southern Tibetan Plateau. Results reveal that major controlling factors are originating from the mid-latitudes.
A basic problem for such investigations is the scarcity of meteorological and glaciological data in High Asia. Therefore, a new data set was generated at the Chair of Climatology of the Technische Universität Berlin, which provides a spatially complete state of the atmosphere over High Asia since 2001, and which was supported by direct field measurements at high altitude (> 5500 m). Since the new data set has a high spatial resolution (up to 2 km), it could be used without statistical corrections for glacier model calculations.
More information about the Regional Reanalysis
This model includes all important physical processes, which determine mass gain (mainly snowfall) and mass loss (mainly melt) on the glacier. Mass gain minus mass loss in a particular year, eventually, yields the so-called annual mass-balance of the glacier. Combining the new data set with the glacier model allowed us to generate an eleven-year time series of the mass fluctuations of Zhadang Glacier (2001-2011), which is located on the southern Tibetan Plateau in the reach of the Indian Summer Monsoon.
Results showed that only a limited number of annual mass-balances can be explained by the activity of the monsoon. However, another factor that impacts mass variability in all years emerged during the analyses: the strength of the regional air flow over the Tibetan Plateau. This strength, in turn, is strongly linked to the intensity of the westerly winds in the mid-latitudes - a linkage that can be traced back to Europe and the North Atlantic. Figuratively, the oscillation of the west wind belt over Germany in early summer will also affect the annual state of a glacier in the very far distance. The new study is therefore the first to show that glacier mass variability in the monsoonal zone of High Asia is also driven by the climate of the mid-latitudes.
This new finding bears great relevance for a better understanding of linkages between large-scale climate change and the climatic environment of the Tibetan Plateau. For example, ice cores from High Asian glaciers contain thousands of years of climate information, but deciphering this information has mostly relied on the activity of the monsoon. Based on the new results, there is now the opportunity to interpret this information in terms of mid-latitude climate as well. This could provide insights into interactions between the tropical and mid-latitude circulation over multiple millennia. Regarding the future, assessments of glacier changes in High Asia will also have to consider how the characteristics of the mid-latitude west winds, and not only those of the monsoon, are changing under global warming.
Mölg T., Maussion F., Scherer D. (2013): Mid-latitude westerlies as a driver of glacier variability in monsoonal High Asia, Nature Climate Change
Link to the paper
Thomas Mölg, Fabien Maussion, Dieter Scherer
Fachgebiet Klimatologie, Technische Universität Berlin