The Washington Post has published an op-ed by Sarah Palin in which she claims that the apparently stolen Climatic Research Unit emails "reveal that leading climate 'experts' ... manipulated data to 'hide the decline' in global temperatures." This is simply false. The emails do not discuss hiding a "decline" in "global temperatures." Indeed, the Post's own news reporting directly contradicts Palin's claim. The Post needs to run a correction and explain to its readers why it allowed this nonsense to be published in the first place.
Palin is referring to a 1999 email in which CRU's Phil Jones wrote:
I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) amd from 1961 for Keith's to hide the decline.
Palin claims that by "hide the decline," Jones is referring to some sort nefarious conspiracy to conceal an actual decrease in "global temperatures." But this is absurd on its face. Here's a chart of average global temperatures published in the Intergovernmental Panel on Climate Change's 2001 report:
Beginning in the mid-1960s, there's a pretty clear long-term warming trend. In other words, there was no "decline" in "global temperatures" for Jones to hide.
So what was Jones talking about? The Washington Post has actually explained it on its news pages. In a December 5 Post article, David A. Fahrenthold and Juliet Eilperin reported that Jones "wrote a colleague that he would 'hide' a problem with data from Siberian tree rings with more accurate local air temperature measurements."
In other words, four days after two Washington Post science reporters explained that Jones was saying that he replaced problematic tree ring data with "more accurate" data from actual temperature measurements, the Post op-ed page allows Palin to claim that Jones was somehow concealing a decline in temperatures that never actually existed.
Media Matters has documented at length the distortions of Jones' 1999 email. And in a December 8 London Times op-ed, Andrew Watson, research professor at the University of East Anglia, debunked the very claim that Palin is now making:
In the one most quoted, the director of the Climate Research Unit (CRU), Phil Jones, talks about using a "trick" to "hide the decline". At first reading, this easily translates as "deceiving [politicians, other scientists, everyone] into believing the world is warming when it is actually cooling".
But it doesn't mean that at all. Jones is talking about a line on a graph for the cover of a World Meteorological Organisation report, published in 2000, which shows the results of different attempts to reconstruct temperature over the past 1,000 years. The line represents one particular attempt, using tree-ring data for temperature. The method agrees with actual measurements before about 1960, but diverges from them after that - for reasons only partly understood, discussed in the literature.
The tree-ring measure declines, but the actual temperatures after 1960 go up. They draw the line to follow the tree-ring reconstruction up to 1960 and the measured temperature after that. The notes explain that the data are "reconstructions, along with historical and long instrumental records". Not very clear perhaps, but not much of a "trick".
The RealClimate blog, which, unlike Sarah Palin's op-ed, is written by actual climate scientists, provided a similar explanation:
Phil Jones in discussing the presentation of temperature reconstructions stated that "I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith's to hide the decline." The paper in question is the Mann, Bradley and Hughes (1998) Nature paper on the original multiproxy temperature reconstruction, and the 'trick' is just to plot the instrumental records along with reconstruction so that the context of the recent warming is clear. Scientists often use the term "trick" to refer to a "a good way to deal with a problem", rather than something that is "secret", and so there is nothing problematic in this at all. As for the 'decline', it is well known that Keith Briffa's maximum latewood tree ring density proxy diverges from the temperature records after 1960 (this is more commonly known as the "divergence problem"-see e.g. the recent discussion in this paper) and has been discussed in the literature since Briffa et al in Nature in 1998 (Nature, 391, 678-682). Those authors have always recommend not using the post 1960 part of their reconstruction, and so while 'hiding' is probably a poor choice of words (since it is 'hidden' in plain sight), not using the data in the plot is completely appropriate, as is further research to understand why this happens.