Monday, April 8, 2013
Prof Lonnie Thompson and colleagues have a new paper in Science Express called "Annually Resolved Ice Core Records of Tropical Climate Variability Over the Past 1800 Years". With annual resolution it becomes worthwhile to compare with measured surface temperatures. I did this with TempLS, using GHCN/ERSST and restricting to an area 1000 km around the location of the Quelccaya site in Peru. The Quelccaya data is here.
This is done partly in response to a thread at Climate Audit, where there was speculation about the possible relationship of the d18O proxy to surface temperature. The standard TempLS analysis is below the step.
The analysis runs from 1900 to 2009. Since Thompson uses the "thermal year" starting for SH in July, I have followed that convention. So what is marked as 2009 is actually Jul 2009-Jun 2010.
Here is a map of all the GHCN/ERSST stations within the radius. ERSST "stations" are the 5x5 lat/lon grid points of the data. The map includes all stations that have reported from 1900-2013, many for only short times. The Quelccaya site is shown with a big blue dot.
Next is a plot of the numbers of stations reporting in each year (for at least 8 months)
Finally, here is the plot of surface temperatures (black) vs Quelccaya d18O. I normalised the d180 data by matching the mean and sd over base 1961-90 to the temperature measure.
Note that the scaling is not to be relied on as I did it by matching. For the first fifty years (with rather small station numbers), there are indications of correlation, but some sranger things recently. The big dip in 1999 in d18O does not seem related to this measure of local temperature. However land temperatures were actually cold, but the 1000 km radius picks up a lot of ocean, which was warm.
Posted by Nick Stokes at 11:24 PM