The global temperature record of the decade just ended -- the warmest on record -- is not really what a lot of climate scientists would have expected. What many of the experts want to know is, why wasn't it warmer?
Why hasn't the rise in temperatures between 2000 and 2009 more closely reflected the inexorable rise in the concentration of carbon dioxide in the atmosphere?
Now an international team of researchers says they may have found the answer. About 10 miles high in the atmosphere, in the lower stratosphere, they have detected a decline in the concentration of water vapor, another potent greenhouse gas.
Atmospheric scientist Susan Solomon of the National Oceanic and Atmospheric Administration's Earth System Research Laboratory in Boulder, CO, and colleagues report online in the journal Science "that stratospheric water vapor represents an important driver of decadal global surface climate change."
Water vapor concentrations in the stratosphere decreased by about 10 percent after the year 2000, the NOAA scientists report, and "this acted to slow the rate of increase in global surface temperature over 2000 to 2009 by about 25 percent compared to that which would have occurred due solely to carbon dioxide and other greenhouse gases."
Other data suggests an increase in water vapor in this region of the atmosphere between 1980 and 2000, "which would have enhanced the decadal rate of surface warming during the 1990s by about 30 percent…"
What causes these shifts in stratospheric water vapor concentration is not clear, the researchers say.
IMAGE: World Meteorological Organization
Tags: Carbon Emissions, Climate Change, Geophysics, Global Warming, Meteorology
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