An explanation for the slowdown in global warming?

A fascinating piece of research has been published in the journal Science today.

The article could go some way in explaining why global warming has slowed down in the last 10 years or so, which I wrote about here, with a more detailed analysis you can read here.

The study by scientists at the US National Oceanic and Atmospheric Administration looked at water vapour (the most powerful greenhouse gas of all) in the stratosphere. Satellite measurements showed that water vapour levels in the stratosphere have dropped 10% since 2000, and when this was fed into a climate model, could have reduced by 25%, over the last decade, the amount of warming that would ordinarily be expected from greenhouse gases.

Their conclusion? The decline in stratospheric water vapour after 2000 should be expected to have significantly contributed to the flattening of the global warming trend in the last decade.

So the 6 million dollar question is this: Was this a natural change in levels of this powerful greenhouse gas. Or did global warming itself, particularly in the 1990's, cause this drop in stratospheric water vapour in the last decade? If so, could we be seeing natural processes putting a brake on global warming?

You can read more detail about this, including what scientists discovered happened to water vapour during the warming that occured during the 1980's and 1990's in an article in today's Guardian.

In it, Susan Solomon who led the research says 'This (new study) shows there are climate scientists round the world who are trying very hard to understand and to explain to people openly and honestly what has happened over the last decade.'

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