Whether its post-IPCC-AR4 fatigue, or a foolish Michaelson-like assumption that we just about know whats going on, but things seem to be rather quiet on the climate front, in terms of real news and results.

Which leaves people footling around for something to talk about, and temperature trends over the past decade, or since 2001 seem to have become a favourite. Climate refuses to behave itself, and insists on having natural variability imposing on longer term trends, which means you can get almost any result you like if you pick your time period. Atmoz has looked at this a bit, but if you prefer pointless statistics without physical understanding you want Lucia, or Prometheus. Lucia asks “is the recent flat trend statistically significant?” and decides it is. Its a fair question, and quite likely her (statistical) analysis is correct. But it doesn’t tell you much about what is going on. Analogy: roll a fair dice a large number of times. Sometimes you’ll get the sequence 6-5-4-3-2-1. Does that mean the next number is zero? Well, of course not. You know the statistics: the next number is one of 1..6, with a 1/6 probability for each of them. In climate, the difference is that we don’t know the statistics: we’re trying to work them out from observations, theory and models. What heppened over the past decade is only part of that.

Lucia’s main point appears to be that current trends are incompatible with IPCC projections. But they aren’t [*]. Because she has misinterpreted the error bars. This is easy to see: compare the width of the error bars on her fig (from ipcc ar4 ch 10 p803 at ~2000 with the wigglyness seen in the observations: the obs are wigglyer. They don’t fit within the error bars. Because the error bars are not supposed to constrain the year-to-year variation. Its not absolutely clear what the error bars are to me, but I don’t think they include natural variability uncertainty (which is only important on the short term).

However, until the temperature obviously and unambiguously turns up again, this kind of stuff is going to continue.

[CIP says much the same, but more humourously]

[* Update: this is a misstatement. What I mean is “But her analysis doesn’t show this”.]