|Launch of a radiosonde balloon.|
A new analysis of weather balloon observations from the last 30 years reveals that the Antarctic has the same global warming signature as that seen across the whole Earth—but three times larger than that observed globally.
The major warming of the Antarctic winter troposphere is larger than any previously identified regional tropospheric warming on Earth. (The troposphere is the lowermost portion of Earth’s atmosphere.) The data show that regional mid-tropospheric temperatures have increased at a statistically significant rate of 0.5° to 0.7° Celsius per decade over the past 30 years.
The results by scientists from British Antarctic Survey are reported this week in Science. The researchers can not unambiguously assign a cause to the tropospheric warming at this stage.
Although the rapid surface warming in the Antarctic Peninsula region has been known for some time, this study has produced the first indications of broad-scale climate change across the whole Antarctic continent.
The warming above the Antarctic could have implications for snowfall across the Antarctic and sea level rise. Current climate model simulations don’t reproduce the observed warming, pointing to weaknesses in their ability to represent the Antarctic climate system. Our next step is to try to improve the models.—Dr John Turner, lead author
Daily launches of weather balloons have been carried out at many of the Antarctic research stations since the International Geophysical Year of 1957-8. The balloons carry instrument packages called radiosondes that measure temperature, humidity and winds up to heights of 20 km or more. Recently many of the old radiosonde records have been digitized and brought together in a project funded by the Scientific Committee on Antarctic Research.
Analysis of the radiosonde data showed a winter season warming throughout the troposphere, which extends up to about 8 km, and cooling in the stratosphere above. The largest warming of almost 0.75 º C per decade was found close to 5 km above the surface. This is more than three times the rate of warming observed for the world as a whole.
The warming has occurred across the whole of the Antarctic and is apparent in the balloon data from Amundsen-Scott Station at the South Pole to the many stations along the coast of East Antarctica. The data are temporally homogeneous.
Although climate change at the surface of the Earth receives wide attention, the atmosphere in recent decades has in fact warmed most some 4-5 km above the surface, with the stratosphere cooling above. There is increasing evidence that levels of greenhouse gases have provided a blanket above the Earth trapping heat at lower levels and giving cooling in the layers above.
Air temperatures in the Antarctic Peninsula region have risen by over 2.5°C in the last 50 years, about 5 times faster than the global mean rate.
“Significant warming of the Antarctic winter troposphere”; J. Turner, T. A. Lachlan-Cope, S. Colwell, G. J. Marshall, W. M. Connolley; Science 31 March 2006: Vol. 311. no. 5769, pp. 1914 - 1917; DOI:10.1126/science.1121652