2007 email: "That the [SST] 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"

Email 536

[David Thompson] 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.