Last month news broke that hackers had illegally obtained and released to the internet about 160MB of private email correspondences between scientists at the East Anglia Climatic Research Unit (CRU). The timing of the release was suspicious because it coincided with preparations for the Copenhagen climate change summit. FOX News and affiliates, followed soon thereafter by right wing and conservative radio personalities and bloggers took up the chant that the emails proved that there was a massive conspiracy and that global warming was now debunked as a fraud. Several sentences in the thousands of emails were taken (out of context) and repeated over and over again as proof of a cover-up. I downloaded all the emails as soon as I could find a site hosting them and started searching through them myself.
The first thing I looked for was that now infamous email from Phil Jones in 1999 wherein he states
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.because it seemed pretty damning. After all, it was being repeated on every FOX channel as the smoking gun. Then I attempted to reconstruct the email conversation that was happening at the time to try to understand what they were talking about. Although I am not a scientist, I did take a lot of science in college and again as a grad student. It became quickly apparent that the "fat mouths" on the radio were either purposely misrepresenting the issue and thus, guilty of the same thing of which they accused Phil Jones; or they hadn't attempted or were unable to put the email into proper context at all which is pretty poor journalism.
The first thing that jumped out at me was that when read in the context of prior emails, the "decline" being discussed wasn't temperature (as suggested) but instead the "temperature proxy" of tree ring data. This is an important distinction. While scientists have an extensive record of tree ring data going back through time, nowhere in the tree rings is there a marking that you can look at and directly read off the temperature from some time in the past. Tree rings can be thin or thick and the thickness definitely tells us whether the tree was growing faster or slower than average that year. This may indicate mean temperature for that year of growth but it might also indicate heavier rainfall that year, or more or less sunlight or any number of other factors which can influence how fast a tree grows. It's not necessarily a 1:1 relation with temperature. Scientists also have a record of temperatures measured directly with instruments, but of course they only have that record available for the time since humans have had these instruments and have recorded the temperature with them (about 150 years). It sure would be nice if we could correlate these two sources of data somehow, and if we could, perhaps we could use the longer tree ring data as a "proxy" for temperature back through time so we could get a picture of what the temperature was back then.
Trouble is, tree-ring thickness correlates pretty well to the recorded temperatures we have only up to a point, then it begins to diverge from it. If the two don't match consistently over this relatively short recent time scale, how can we say that tree ring data can actually tell us anything useful about temperature in the deep past? Perhaps if the scientists could find a mathematical relation (also commonly referred to as a "computational trick" or simply "trick") which could be used to make the two trend lines match up better then maybe they could apply that relation to the tree ring data for the past and be relatively comfortable that the temperature they derive from it was accurate.
So what Mr Jones was talking about apparently wasn't so sinister after all. He was talking about the apparent decline in temperatures shown by tree ring data since the 50s. This isn't REAL temperatures at all. The REAL temperatures as measured by instruments and as recorded all over the world (not just one station in East Anglia) and published daily in almost every newspaper on earth (and which you can go look up if you're so inclined) show an INCREASE in global temperature. So what this email is showing is that (in 1999) climate scientists were seeing a decline in the apparent temperature they were deriving from tree ring data (from trees alive and growing around the world) which didn't match the actual temperatures (which were rising). Obviously a big problem if you wanted to use the more ancient tree ring data to say anything at all - hence the need for some kind of computational model to fit the lines (or "hide the decline" of apparent temperatures).
There's a whole lot more in the hacked emails to look at if you have some time. Scientific papers you might otherwise have had to pay for, climate programs written in Fortran (yuck) that you can play with, as well as thousands of emails showing not a hint of conspiracy but rather normal scientific discussion, argument and debate on an important issue. Instead of writing more on this topic, I think I will refer you instead to a good summary video by an informed journalist. He's posted several fantastic videos on Youtube about climate change with the aim of making the science more approachable for the layman.