Decreased Water Vapor in Atmosphere Slowed Last Decade's Warming

water vapor stratosphere image

image: NOAA

Here's an interesting addition to global warming science: The National Oceanic and Atmospheric Administration says that decreases in water vapor ten miles above the Earth have slowed by one quarter the amount of surface warming that has occurred in the past ten years--which NASA recently confirmed was the hottest decade on record--while more water vapor in the 1990s increased warming:However these variations in water vapor don't change "the fundamental conclusion that that world has warmed and that most of that warming has to do with greenhouse gas emissions caused by man," says report lead author Susan Solomon. (New York Times)

10% Decrease in Water Vapor = 25% Less Warming
The report, published today in the online edition of the journal Science, shows that stratospheric water concentrations decreased by 10% after the year 2000, leading to a 25% lower rate of global surface temperature increase from 2000-2009 than which would have occurred only due to carbon dioxide and other greenhouse gases.

These changes occurred precisely in a narrow part of the stratosphere where they would have the biggest impact on climate. The reason for the decline in water vapor is unknown.

30% More Warming in 1990s
Conversely, and relying on what the authors describe as "more limited data" from 1980-2000, increases in stratospheric water vapor during the 1990s actually led to a 30% increase in observed warming.

NOAA says this is the first report to link specific variations in observed warming to changes in stratospheric water vapor.

Here's the original Science article: Contributions of Stratospheric Water Vapor to Decadal Changes in Rate of Global Warming [subscription or pay-per-read required]

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