Wednesday, March 20th 2013, 5:51 AM EDT
A new study shows that 40% of the warming we have seen the past 50 years can be ascribed not to man-made global warming but the so-called Atlantic Multidecadal Oscillation (AMO).
This 50-80 year cycle is well-documented over the past 353 years.
Look at the top graph of global temperatures. The blue line indicates the long swings -- steep temperature increase 1910-1940, slight cooling till 1975, another steep increase from 1975-2005 and now a standstill.
The UN interpreted this as “accelerating warming trends” -- over the past 150 years temperatures rose 0.05oC/decade, over the past 100 years they rose 0.07oC/decade and the last 25 years a full 0.15oC/decade.
But if we take out the AMO, which is not man-made, we get the lower image -- much clearer global warming over the past 100 years at pretty much a stable rate of 0.08oC/decade, no matter when you look.
There is still man-made global warming. But -- according to this paper -- only about half as much as what we used to think.
Here is the paper: Proceedings of the National Academy of Sciences of the United States of America, Using data to attribute episodes of warming and cooling in instrumental records
http://www.pnas.org/content/110/6/2058.abstract
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