Chris Ho-Stuart -
I agree with your point about length of trends, and generally would go even further..
You mention that -
From 1979-1999 onwards, the HadCRUT 20 year window has never gone below 0.15.
I keep an eye on the trends since 1990 for the sole reason that this was the year of the IPCC FAR. I’d therefore make the obsevartion that since then, Hadcrut3 has a trend of 0.14 [as does RSS)]
There are of course caveats aplenty to be had. Those with a ‘cooling’ agenda might point out that had Pinatubo erupted in 2009 rather than 1991, the trends would have been less than 1.0.
I’m not making great claims for these things, but saying that even a 20yr moving window has its limitations, as I’m sure you know. One obvious example of this is the likely trend of 1997-2006. Barring very dramatic changes, it will have a very low positive trend. I don’t think this is significant, but making a point of the 20 year trends of the past opens you up a little to the ‘what about 1997-2006!!’ if it is indeed very low [or even negative].
