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The study by Keenlyside et al. tested whether a simplified climate model could make decadal (short-term by climate standards) forecasts. At issue is realistically simulating the many internal variations in the climate system - oscillations like the Atlantic Multi-decadal Oscillation (why people claim Atlantic hurricane activity 'naturally' varies over time) and the Pacific Decadal Oscillation - that make some decades warmer or cooler than others. The authors developed a modeling approach that exhibited some 'skill', to use the meteorologists term, in hindcasting previous ten-year periods. All in all, it is a reasonable effort; I'll spare a detailed analysis of the limits of their methodology here (but see William Connolley for a critical reading).
At the end of the manuscript, it was used to forecast temperatures over the next ten years (figure). The model forecasts a leveling off in the global temperature rise over the next decade (green / black lines), due to these internal variations in the climate system, followed by a continuation of the temperature rise.
Nowhere does it say climate change is over. This is a paper about whether models can make decadal predictions. The results confirm what we know, that internal variability is superimposed on any long-term warming trend. The global warming projections you see often look smooth or monotonic because they are averages of many individual model simulations or "realizations" of the climate (averaging them together reduces the "noise" in the data). So the paper doesn't contradict the existing consensus on a long-term rise in temperatures.
Their model forecasts the possibility that temperatures will not increase in some decades like the next decade - which is NOT the same as saying that temperatures will decrease - but will increase more in other decades. Look at the figure: the next decade is WARMER than any of the previous decades. Nothing about the end of global warming. Yet the story that hit the press was "scientists predict global warming may stop" (Telegraph).
As with the Darfur lake fiasco last year, the authors of the press release may shoulder some of the blame. The opening "Global warming may take a short break" played up an angle sure to draw interest from the media. That does not absolve the authors of the global warming may stop silliness, both in the traditional media and that grand echo-chamber we call the blogosphere. It is not clear many of them read the press release, let alone the paper, (Pielke's flubbing the numbers seems proof of that) as the release very clearly states that the goal of the study was to look at decadal variability, and included this important quote from the authors:
"Just to make things clear: we are not stating that anthropogenic climate change won’t be as bad as previously thought”, explains Prof. Mojib Latif from IFM-GEOMAR. “What we are saying is that on top of the warming trend there is a long-periodic oscillation that will probably lead to a to a lower temperature increase than we would expect from the current trend during the next years”, adds Latif. “That is like driving from the coast to a mountainous area and crossing some hills and valleys before you reach the top”, explains Dr. Johann Jungclaus from the MPI for Meteorology. “In some years trends of both phenomena, the anthropogenic climate change and the natural decadal variation will add leading to a much stronger temperature rise."
The good news is that there are people like Andy Revkin of the NY Times (Dot Earth) out there, who tends to avoid the cheap stunt headlines and stories. Revkin's NY Times piece was like a pre-empitive strike against all the silliness to come.
[Update: For more, try this post from the prolific Joe Romm.]
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