ARGUMENTS have again broken out over whether the Earth鈥檚 troposphere is warming. At issue is whether human activity drives climate change.
Sceptics often cite a 10-year-old analysis of satellite data by John Christy at the University of Alabama in Huntsville, which apparently shows negligible warming of the troposphere 鈥� the lowest 14 kilometres of the atmosphere. If greenhouse gases were having an impact, this region would heat up.
But mainstream climate scientists claim that Christy鈥檚 analysis ignored biases in the data, for example those due to the decaying orbits of the satellites and uncertainties in calibrating different satellites.
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Now a second analysis of the same data, to be published shortly by Carl Mears at Remote Sensing Systems, a research company in Santa Rosa, California, suggests warming has been happening after all 鈥� at roughly 0.1 掳C a decade. That鈥檚 in line with thermometer measurements at the Earth鈥檚 surface and predictions by climate models.
The two analyses are compared by Ben Santer of the Lawrence Livermore National Laboratory, California, in an online issue of Science (DOI:10.1126/science.1082393). Santer says that Mears鈥檚 study is more consistent with climate models, and the conflicting interpretations mean sceptics can no longer claim the satellite data disproves theories about global warming. 鈥淭he message I take home is that the uncertainties in satellite-based estimates are much larger than Christy has claimed,鈥� he told New Scientist.
But Christy has instantly hit back at this criticism. He says that Santer鈥檚 comparison is 鈥渞ather odd鈥� as it uses theories to judge the accuracy of data, rather than the other way round. And the day after Santer鈥檚 article was published, details were released of an analysis by Christy of data collected from weather balloons, which will be published in the Journal of Atmospheric and Oceanic Technology.
He concedes the balloons do show warming, of about 0.07 掳C a decade. But that is 鈥渟ubstantially less than the warming forecast by most models, and not entirely out of the range of climate change we might expect from natural causes.鈥�