Global Average Temperature Cools a Bit in November, But No Pause in Global Warming — And There Never Was One

How temperatures in November departed from the long-term average is depicted in this map released by NASA today (Dec. 14, 2014). Much of North American experienced unusually cool temperatures during the month. (Source: NASA/GISS) This past November was the ninth warmest globally in a record extending back to 1880, according to data released today by NASA. | Update 12/15/14: The National Oceanic and Atmospheric Administration came out with its own, independent report today. It ranks November 2014 as the 7th warmest on record. Their data suggest that 2014 is still on track to be the warmest year globally on record. | This represents a bit of a cool-down from October, which was the warmest globally. What happened? The answer is weather. In the map above, check out that big blue blob sitting over most of North America (with California and Alaska being the notable exceptions). Temperatures here were as much as 4 degrees C cooler than the long term average, helping to bring down the global average temperature for the month. Thanks to the just announced climate agreement in Peru, this topic is threaded with politics even more intensely now than usual. So you may hear a familiar chorus of politicians and pundits using this one month to advance a familiar meme: there has been no global warming since 1998. If you do hear this, never mind that the past 12 months have been the second warmest (according to NASA's data; NOAA's data will be released soon), and also that a balmy December could still qualify 2014 as the warmest on record. None of that matters. Because the meme is no more than that: an oft-repeated idea spread rapidly on the Internet. And wrong. I explored the so-called "hiatus" meme in Discover's Year-in-Science issue, which was published a couple of weeks ago. Then, on December 4th, Stefan Rahmstorf, a climatologist with the Potsdam Institute for Climate Impact Research in Germany, published a fascinating and incisive scientific take-down of the idea. I think it's "dispositive," as my lawyer friends would say. So I decided to revisit the topic and try my hand at explaining Rahmstorf's most important points for non-scientific readers.  I must admit that for my Year-in-Science story, I wrestled with what word to use to describe what has really been happening — a slowdown in rising temperatures since about 1998. That's because some scientific papers talked about an apparent "pause" or "hiatus" (for example, this one) in what had previously been a more or less steady upward trend in global average surface temperature. I used italics there because the Earth's climate system consists of much more than what's happening at the surface. In fact, as many papers pointed out, there has been no real overall pause: the Earth system has been continuing to accumulate heat, thanks to humankind's emission's of carbon dioxide and other greenhouse gases. It's just that a lot of that heat seems to have been going into the oceans, slowing the rise in temperatures at the surface. Moreover, it's important to emphasize that each of the last three decades has been warmer at the surface than every preceding one back to the start of modern record keeping in the 1880s. Even so, scientists have used the words "pause" and "hiatus" to describe what has been happening to the long-term warming trend at the surface of the Earth. Rahmstorf uses a series of graphs to illustrate why this is incorrect.