Revisiting historical ocean surface temperatures

and are important in a few key time-periods – the 1940s (because of issues highlighted previously), the 1860s to 1890s (more extensive data), and perhaps the last few years (related to more minor changes in technologies and corrections). The biggest difference around 1946-8 is just over 0.2ÂșC.

One odd feature of the HadSST2 collation was that the temperature impact of the 1883 Krakatoa eruption – which is very clear in the land measurements – didn’t really show up in the SST. Thus comparisons to model simulations (which generally estimate an impact comparable to that of Pinatubo in 1991) showed a pretty big mismatch (see Hansen et al (2007)). With the larger amount of data in this period in HadSST3, did the situation change?

Figure: 1880’s comparison of (left) global surface air temperature anomalies using HadSST2 (as part of GISTEMP) and the GISS AR4 simulations, (right) global SST estimates from HadSST2 and HadSST3.

It seems clear that the new data (including HadSST3) will be closer to the models than previously, if not quite perfectly in line (but given the uncertainties in the magnitude of the Krakatoa forcing, a perfect match is unlikely). There will also be improvements in model/data comparisons through the 1940s, where the divergence from the multi-model mean is quite large. There will still be a divergence, but the magnitude will be less, and the observations will be more within the envelope of internal variability in the models. Neither of these cases imply that the forcings or models are therefore perfect (they are not), but deciding whether the differences are related to internal variability, forcing uncertainties (mostly in aerosols), or model structural uncertainty is going to be harder.

So how well did the blogosphere do?

Back in 2008, a cottage industry sprang up to assess what impact the Thompson et al related changes would make on the surface air temperature anomalies and trends – with estimates ranging from complete abandonment of the main IPCC finding on attribution to, well, not very much. While wiser heads counselled patience, Steve McIntyre predicted that the 1950 to 2000 global temperature trends would be reduced by half while Roger Pielke Jr predicted a decrease by 30% (Update: a better link). The Independent, in a imperfectly hand drawn graphic, implied the differences would be minor and we concurred, suggesting that the graphic was a ‘good first guess’ at the impact (RP Jr estimated the impact from the Independent’s version of the correction to be about a 15% drop in the 1950-2006 trend). So how did science at the speed of blog match up to reality?

Here are the various graphics that were used to illustrate the estimated changes on the global surface temperature anomaly:

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