“Hide the decline”: why it’s dishonest

Needless to say, the biggest news story in the world of global warming in the past week has been the hacking of the East Anglia Climate Research Unit. When the news first broke, the big headline was an email by Phil Jones from 1999 and one damaging 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) amd from 1961 for Keith’s to hide the decline.”

This line has prompted much debate, with some on the right claiming this is fraud or that it’s proof the global warming alarmists are adding fake data or whatever. This line of thought has been attacked, with Real Climate leading the way:

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.

Others have said it’s just a way to make the data look pretty, or that “trick” is just the natural jargon. Needless to say, the truth is a bit more complicated.