I try to make it a habit to criticize bad analyses from "my side" of certain debates. I find this to be a good habit that keeps one from falling for poorly constructed but ideologically tempting arguments.
Here is my example this week, from climate skeptic Steven Goddard. I generally enjoy his work, and have quoted him before, but this is a bad chart (this is global temperatures as measured by satellite and aggregated by RSS).
He is trying to show that the last 17+ years has no temperature trend. Fine. But by trying to put a trend line on the earlier period, it results in a mess that understates warming in earlier years. He ends up with 17 years with a zero trend and 20 years with a 0.05 per decade trend. Add these up and one would expect 0.1C total warming. But in fact over this entire period there was, by this data set, 0.3C-0.4C of warming. He left most of the warming out in the the step between the two lines.
Now there are times this might be appropriate. For example, in the measurement of ocean heat content, there is a step change that occurs right at the point where the measurement approach changed from ship records to the ARGO floats. One might argue that it is wrong to make a trend through the transition point because the step change was an artifact of the measurement change. But in this case there was no such measurement change. And while there was a crazy El Nino year in 1998, I have heard no argument from any quarter as to why there might have been some fundamental change in the climate system around 1997.
So I call foul. Take the trend line off the blue portion and the graph is much better.