date: Tue, 27 Nov 2007 10:48:58 +1100
from: David Thompson <davet@atmos.colostate.edu>
subject: a quick comment and a quick question
to: Phil Jones <p.jones@uea.ac.uk>

   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
