Mysterious changes in the stratosphere may have offset greenhouse effect.
A loss of water vapour from the Earth’s stratosphere may have been behind the last decade being cooler than expected.NASA
A puzzling drop in the amount of water vapour high in the Earth’s atmosphere is now on the list of possible culprits causing average global temperatures to flatten out over the past decade, despite ever-increasing greenhouse-gas emissions.
Although the decade spanning 2000 to 2009 ranks as the warmest on record, average temperatures largely levelled off following two decades of rapid increases. Researchers have previously eyed everything from the Sun and oceans to random variability in order to explain the pause, which sceptics have claimed shows that climate models are unreliable.
Now a team led by researchers at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, report that a mysterious 10% drop in water vapour in the stratosphere — the atmospheric layer that sits 10–50 kilometres above Earth’s surface — since 2000 could have offset the expected warming due to greenhouse gases by roughly 25%. Just as intriguingly, their model suggests that an increase in stratospheric water vapour might have boosted earlier warming by about 30% in the 1980s and 1990s. Read more
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