date: Tue, 27 Nov 2007 10:48:58 +1100 from: David Thompson subject: a quick comment and a quick question to: Phil Jones Phil, The comment.... Thanks for the thoughts on the volcano plots. I've spent the last few days playing with different analyses, and I think I'm converging on the main points to make in the paper. It's my impression that almost all aspects of the volcanic signal have been discussed in the literature, except for the longish timescale suggested by the residual data and the detrending. For sure the timescale is sensitive to the detrending, and I'll be very careful about that in the writing. But I think using the residual data we can get folks chatting about the possibility that volcanoes impact SSTs much longer than the ~2-4 years suggested by the current literature. Anyway.... that's how I'm leaning on the results. I should have some text ready soon... The question.... As for the dip in 1945. After iterating with John Kennedy, it appears that the dip in 1945 corresponds to a sudden drop in US measurements in Aug 1945 (the US measurements were known to be biased warm, so the cooling is consistent with the loss of US data). But it is also now clear that the SST is fraught with many instrument changes between the 30s and 1961. So a conclusion we'll likely make is that the trend in SSTs between 1900 and the present is reliable, but the behavior of the time series from the 1930s to the 1960s is not. That the data are so unreliable between the 30s and 60s means we don't know for sure what happened in terms of global-mean temperatures during that period. In fact, if you blank out the data from the 30s to the 60s, you can actually imagine the globe warming weakly but continuously during that period... Hence, the only real evidence we have of a midcentury about-turn in global warming comes from the land data. Are there any similar data issues in the land data during the period ~1939-1960? Thanks, Dave -------------------------------------------------------------------- -------------------------------------------------------------------- David W. J. Thompson www.atmos.colostate.edu/~davet Dept of Atmospheric Science Colorado State University Fort Collins, CO 80523 USA Phone: 970-491-3338 Fax: 970-491-8449