Wednesday, December 07, 2011

Two recent papers clarify climate change cause, continuation

(edited - plus a Thursday update from study author Knutti below.)
Two peer reviewed papers, taking different approaches, document the human influence on and the continuation of global warming.

In Environmental Research Letters, Foster & Rahmstorf stripped out the effect of short-term natural variability on temperature on all the available global land+ocean datasets from 1979-present, and found that with natural variability removed, global temperature has continued to rise, including the last decade, with 2009-2010 the warmest adjusted years overall. (link: The Real Global Warming Signal; also RealClimate addressed it here. )

And in Nature Geoscience, Huber and Knutti find that at least 74% of the warming since 1950, and most likely more, has been manmade:
"Our results show that it is extremely likely that at least 74% of the observed warming since 1950 was caused by radiative forcings, and less than 26% by unforced internal variability. Of the forced signal during that particular period, 102% (90–116%) is due to anthropogenic and 1% (−10 to 13%) due to natural forcing…"
(Link: It’s “Extremely Likely That at Least 74% of Observed Warming Since 1950″ Was Manmade; It’s Highly Likely All of It Was )

Thursday update: likely a lot more than 74%; in email, Knutti said:
"Our best estimate is that ALL of the observed warming since 1950 is man-made. But there is some uncertainty from natural climate fluctuations. So it's possible that human have caused a bit more than observed, compensated by natural variation, or a bit less than observed, with natural variations being positive. But in any case we are almost certain that the human contribution is more than three quarters."

"We will be judged by those who come after us, both by what we did do and what we didn't do, in the time given to us."

No comments: