Heatwave on the top of the world

March 02, 2007

The French Intergovernmental Panel on Climate Change (IPPC, or GIEC in French) has just announced the conclusions of its 4th report, which restates that global warming has increased the average temperature by 0.74°C over the last century. However, there is very little information about some parts of the planet, such as central Asia. A new study by French researchers from the Laboratory of Glaciology and Geophysics of the Environment (LGGE, CNRS / Université Joseph Fourier, Grenoble, France) and the Laboratory of Sciences of the Cliamte and the Environment (LSCE / IPSL, CEA / CNRS / Université de Versailles Saint-Quentin, France), in collaboration with Chinese, Russian and American researchers, proves that the recent warming has also affected the ice cap on Mount Everest, in the heart of the Himalayas. This result was published on February 7, 2007 in the European Journal "Climate of the Past".

Relatively little is known about climate change in the Himalayas and the Tibetan plateau. There are very few meteorological stations, and instrumental records from glaciers, lakes or tree growth rings are rare and difficult to interpret. However, in 2001 and 2002, Chinese scientists drilled three ice cores in the eastern summit of the East Rongbuk glacier that covers the north pass of Mount Everest, at 6518 meters above sea level. These ice cores were analyzed in collaboration with the LGGE and the LSCE, and they have shown that a new climate marker exists, the ice core gas content, which can reconstruct the changes in summer temperatures on this very high site.

At these altitudes, the surface snow partially melts in the summer and the melt water percolates1 through the snow cover to refreeze deep down. This process affects the density and size of air bubbles contained in the ice, that is, its gas content. So the gas content is directly related to the intensity of the summer ice melt. By measuring accurately the gas content throughout two of the three ice cores taken from the top of Everest, researchers have been able to follow the changes over time, going right back to 2,000 years ago. They noted a very marked decrease in the quantity of gas trapped in the 20th century ice, compared with the content in older ice, which reflects recent increases in the summer melts on the glacier surface. Although the team has not as yet been able to quantify exactly the temperature change over time using this new marker of trapped gas, their research clearly shows that global warming has also affected the ice cap on top of the world.
1. Melt water flows down through the snow under the effect of gravity.

In France, this work was supported by CNRS' international French-Chinese scientific cooperation program (in the context of the "CLEAH2 project"), and in China by the French Embassy.

2. Climate and Environment in Antarctica and the Himalayas

Glaciological drilling on the sides of Mount Everest. Chinese Himalayas. © S. Hou, CAREERI, China


Summer temperature trend over the past two millennia using air content in Himalayan ice. Hou S., Chappellaz J., Jouzel J., Chu P.C., Masson- Delmotte V., Qin D., Raynaud D., Mayewski P.A., Lipenkov V.Y. et Kang S., Climate of the Past 3, 89-95, 2007.

Online at: http://www.clim-past.net/3/89/2007/cp-3-89-2007.pdf


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Jérôme Chappellaz
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