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The Berkeley Earth Surface Temperature project (BEST), under the overall leadership of astrophysicist Richard Muller, has just published a new paper in the journal Geoinformatics and Geostatistics. Richard Rohde is the first author.

Rohde R, Muller RA, et al (2013) "A New Estimate of the Average Earth Surface Land Temperature Spanning 1753 to 2011", Geoinformatics and Geostatistics, vol 1, doi:10.4172/gigs.1000101

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We report an estimate of the Earth’s average land surface temperature for the period 1753 to 2011. To address issues of potential station selection bias, we used a larger sampling of stations than had prior studies. For the period post 1880, our estimate is similar to those previously reported by other groups, although we report smaller uncertainties. The land temperature rise from the 1950s decade to the 2000s decade is 0.90 ± 0.05°C (95% confidence). Both maximum and minimum daily temperatures have increased during the last century. Diurnal variations decreased from 1900 to 1987, and then increased; this increase is significant but not understood. The period of 1753 to 1850 is marked by sudden drops in land surface temperature that are coincident with known volcanism; the response function is approximately 1.5 ± 0.5°C per 100 Tg of atmospheric sulfate. This volcanism, combined with a simple proxy for anthropogenic effects (logarithm of the CO2 concentration), reproduces much of the variation in the land surface temperature record; the fit is not improved by the addition of a solar forcing term. Thus, for this very simple model, solar forcing does not appear to contribute to the observed global warming of the past 250 years; the entire change can be modeled by a sum of volcanism and a single anthropogenic proxy. The residual variations include interannual and multi-decadal variability very similar to that of the Atlantic Multidecadal Oscillation (AMO).

The new thing here is their extension of their gridded temperature data series back to 1753, a century deeper into the past than similar research efforts. That century included several very powerful volcanos, which allows them to obtain a better estimate of the effect of volcanism on global mean temperature.

Their statistical model of the influences on global mean temperature included atmospheric carbon dioxide, incoming solar radiation, and volcanism. By subtracting out the statistically significant effects and comparing the residuals to the Atlantic Meridional Oscillation (AMO), they were able to show that the AMO is correlated with global mean temperature. The AMO is a temperature series, so it is not terribly surprising that its fluctuations are correlated with the fluctuations in global mean surface temperatures (that same comment holds for the faster ENSO series), but this is still an important result.

A secondary but scientifically important benefit of the new series is that its uncertainties are smaller than any previous study. I imagine that this reduction is due to the innovative way in which BEST was able to incorporate all fragments of data from temperature stations -- unlike Hadley, GISS, etc, which use only extended fragments.

Over and above their scientific results, it is very interesting to look at the graphs in the report. Now that these data extend back 250 years, these graphs are beginning to give a better feeling of natural and "unnatural" (i.e. anthropogenic) variation.

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