Has Global Warming taken a break?

Last week the English paper Mail on Sunday had a story claiming that a Met Office report shows global warming had stopped 16 years ago. The article, written by David Rose, caused a storm and was contested in a piece Dana Nuccitelli had written for Skeptical Science and published by the Guardian. It is certainly no accident that these two papers aligned themselves in predictable ways. And it is no accident that corresponding blogs reacted in predictable ways.

What is the fuss about? The Mail article shows temperature data from 1997 to 2012 with no warming trend.

The lack of warming had been acknowledged by leading climate scientists for a while, as reported for example by Greenwire here:

"The question itself, while simple sounding, is loaded. By any measure, the decade from 2000 to 2010 was the warmest in modern history. However, 1998 remains the single warmest year on record, though by some accounts last year tied its heat. Temperatures following 1998 stayed relatively flat for 10 years, with the heat in 2008 about equaling temperatures at the decade's start. The warming, as scientists say, went on "hiatus."

The hiatus was not unexpected. Variability in the climate can suppress rising temperatures temporarily, though before this decade scientists were uncertain how long such pauses could last. In any case, one decade is not long enough to say anything about human effects on climate; as one forthcoming paper lays out, 17 years is required.

Greenwire quotes Hansen, Santer, Trenberth, Solomon and others. The story appeared last October. Now another year has passed and we are coming close to the magic number 17. While the eminent climate scientists accepted the hiatus as a fact, there is no consensus on explanations. The Guardian story quoted above tries to make the stronger case, saying that there is a "most likely" positive trend.

The trend in the HadCRUT4 global surface temperature dataset since 1997 is 0.084 ± 0.152°C per decade (although we have not yet updated the HadCRUT4 data, the GISS and NCDC datasts show a similar warming trend since 1997). While the trend is not statistically significant, the central value is positive, meaning the average surface temperature has most likely warmed over this period.

I am not sure what "most likely" means in this context. But it surely demonstrates that some in the global warming debate think a non-positive trend could be a problem (for what: for AGW theory? For climate policies? For both?). Yesterday Michael E. Mann tweeted that Rose and Judith Curry  "double down w/ their denial of #globalwarming (http://bit.ly/Rfh6Vx ). Debunked by @Guardian". So for him this story is part of the denial machine, and something big is at stake.

Judith Curry is quoted in the Mail Online, saying: "Nothing in the Met Office’s statement .  .  . effectively refutes Mr Rose’s argument that there has been no increase in the global average surface temperature for the past 16 years." And addressing climate scientists uncomfortable with the hiatus, she wisely advises:

Use this as an opportunity to communicate honestly with the public about what we know and what we don’t know about climate change. Take a lesson from other scientists who acknowledge the “pause”.

I case you have not seen it, there is a relevant discussion on the thread Interview with Eduardo Zorita about the production of stable facts in (climate) science. I conclude from the "hiatus story" that there is no evidence either way: at present, it neither confirms nor refutes anthropogenic global warming.

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