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.
It certainly looks very bad. I've been disappointed by the scientific response to this; their explanations and denials have not been very clear or easy to summarize, and it was only today that I came across a good explanation of what this sentence was talking about.
The use of the word "trick" is pretty easy to explain; lots of people use "trick" to mean "technique". Searching the web will find lots of examples, like this one:
There's also a little trick you can do with map. map(None, l, m, ... z) will return a list of tuples [(l[0], m[0], ... z[0]), (l[1], m[1]... z[1]), ...
"Hide the decline" is more worrying, since it smacks of covering something up. The whole thrust of climate change is that temperatures are increasing, so hiding a decline is suspicious. The e-mails were leaked two weeks ago, so I'm disappointed to have seen a good explanation of this aspect of Climategate only today, written by Dr Jeff Masters at his Weather Underground weblog:
Another area of concern is over a graph Dr. Jones helped construct in 1999 showing the "hockey stick" of Earth's surface temperature going back 1,000 years. This graph combined instrumental measurements made since the 1800s with older paleoclimate data (including data from tree rings) to show a continuous 1,000 year record of Earth's temperatures. The paleoclimate data after 1960 show a bogus decline in Earth's temperatures that does not agree with what modern thermometers have been measuring, due to a well-known variation in tree ring thickness as a function of time, referred to as "the decline". Thus, Jones elected to toss out the bogus paleoclimate data (using a "trick" to "hide the decline") rather than present it in the graph.
Dr Masters's entry also has a graph showing the reconstructed historical temperature graph, the instrumental graph of temperature, and the diverging line of the tree ring results. The initial discussion at realclimate.org also mentioned it, but the reference is very short, very dry, and just refers to the original papers. It would have been better for the original author to have written "to discard the recent erroneous data", but who among us is so careful in a private e-mail to co-workers?
I am curious about the hack. Was it carried out by some random hacker who was just poking around U. of East Anglia's servers? Or was it a targeted attack? Was it funded by someone? It would be very interesting to know, though it'll probably be impossible to track down who the intruder was.
Update: in a story in the National Post, a U. of Victoria researcher claims they've had hacking attempts, two physical break-ins and one computer stolen. This might not be anything special -- hacking attempts could just be the usual random script kiddy scans, and computers occasionally disappear in universities -- but it's more circumstantial evidence, and makes me more interested in seeing an investigation.