I wanted to know what the deal was with this and whether there was any real steam to the issue. The most criticized line “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” may leave some to believe that that the data was fudged. The issue of the debate has to do with using historical temperature data constructed from tree rings and then matching them with actual temperature data measured recently, which in turn show contradicting trends. To elaborate, from The Island of Doubt:
… a graph that shows how temperatures inferred from tree-ring records since about 1850 (the “proxies”) are a pretty good match for actual temperature records derived from thermometers right up until the 1980s. After that, the tree-ring data begin to show lower temperatures than were actually recorded.
Just why tree rings no longer provide useful proxy data for temperatures is not known. There are several theories, many of which suggest that climate change itself is the problem. Trees no longer grow as they once did before the climate started changing so rapidly. But the point is, there is no question that tree-ring growth rates of the past — before we had thermometers — can serve as useful proxies for historical temperature data. They are much less useful now, but that doesn’t matter so much because we have actual temperature records. All of this was sorted out back in 1998. It’s not new, nor even particularly interesting, to anyone familiar with the science.
Realclimate.org comments that this issue was already dealt with in climate circles and proves how the emails were taken out of context.
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.
Cynicism in scientific debate, especially as heated as climate change, is always warranted, but such unethical means of obtaining information to try and carryout well-placed press before important political undertakings is not an effective way to prove one’s point. All of which prove how much this really is just bunk.