We see occasional references in our discussions here to a “cooling phase” over the past decade or so. It’s often evoked in arguments against the case for global warming. Of course, in the centuries-long span of the Earth’s climate patterns, a decade or so is a mere blip on the screen.
Now a climatologist at Lawrence Berkeley National Lab has co-authored a paper that warns against using “periods of a decade or two” to argue the case one way or the other (we also often hear people use temperature data from recent hotter years as evidence for global warming).
Andrew Revkin summarizes the findings in his blog for the New York Times.
Wehner works in the Computational Research Division at LBNL and co-authored the paper with NOAA scientist David Easterling of the National Climatic Data Center, in Ashville, NC. Easterling wrote the Center’s FAQ page on global warming, in which he includes this answer to the question of whether the global climate is warming:
“Global surface temperatures have increased about 0.74°C (plus or minus 0.18°C) since the late-19th century, and the linear trend for the past 50 years of 0.13°C (plus or minus 0.03°C) per decade is nearly twice that for the past 100 years. The warming has not been globally uniform. Some areas (including parts of the southeastern U.S. and parts of the North Atlantic) have, in fact, cooled slightly over the last century. The recent warmth has been greatest over North America and Eurasia between 40 and 70°N. Lastly, seven of the eight warmest years on record have occurred since 2001 and the 10 warmest years have all occurred since 1995.”
As for the geographic fluctuations, Robert Bornstein of San Jose State has produced data showing a general cooling trend along the California coast over the past 30 or 40 years. But he’s quick to point out that the anomaly is most likely a result of, not an argument against the broader global warming trend.