A 10% drop in water vapor ten miles above Earth’s surface has had a big impact on global warming, say researchers in a study published online January 28 in the journal Science. The findings might help explain why global surface temperatures have not risen as fast in the last ten years as they did in the 1980s and 1990s.
Observations from satellites and balloons show that stratospheric water vapor has had its ups and downs lately, increasing in the 1980s and 1990s, and then dropping after 2000. The authors show that these changes occurred precisely in a narrow altitude region of the stratosphere where they would have the biggest effects on climate.
“Current climate models do a remarkable job on water vapor near the surface. But this is different–it’s a thin wedge of the upper atmosphere that packs a wallop from one decade to the next in a way we didn’t expect,” said Susan Solomon, National Oceanic and Atmospheric Administration (NOAA) senior scientist and first author of the study.
Since 2000, water vapor in the stratosphere decreased by about 10%. The reason for the recent decline in water vapor is unknown. The new study used calculations and models to show that the cooling from this change caused surface temperatures to increase about 25% more slowly than they would have otherwise, due only to the increases in carbon dioxide and other greenhouse gases.
The stratosphere is a region of the atmosphere from about eight to 30 miles above the Earth’s surface. Water vapor enters the stratosphere mainly as air rises in the tropics. Previous studies suggested that stratospheric water vapor might contribute significantly to climate change. The new study is the first to relate water vapor in the stratosphere to the specific variations in warming of the past few decades.
Source: NOAA
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