by Judith Curry
The five-year mean global temperature has been flat for the last decade, which we interpret as a combination of natural variability and a slow down in the growth rate of net climate forcing. – James Hansen et al.
Jim Hansen et al. have written a remarkable document titled Global Temperature Update Through 2012. Excerpts:
An update through 2012 of our global analysis reveals 2012 as having practically the same temperature as 2011, significantly lower than the maximum reached in 2010. These short-term global fluctuations are associated principally with natural oscillations of tropical Pacific sea surface temperatures summarized in the Nino index in the lower part of the figure. 2012 is nominally the 9th warmest year, but it is indistinguishable in rank with several other years, as shown by the error estimate for comparing nearby years. Note that the 10 warmest years in the record all occurred since 1998.
The current stand-still of the 5-year running mean global temperature may be largely a consequence of the facr that the first half of the past 10 years had predominantly El Nino conditions, and the second half had predominantly La Nina conditions.
The approximate stand-still of global temperature during 1940-1975 is generally attributed to an approximate balance of aerosol cooling and greenhouse gas warming during a period of rapid growth of fossil fuel use with little control on particulate air pollution, but quantitative interpretation has been impossible because of the absence of adequate aerosol measurements.
Climate change expectations. The continuing planetary imbalance and the rapid increase of CO2 emissions from fossil fuel assure that global warming will continue on decadal time scales. Moreover, our interpretation of the larger role of unforced variability in temperature change of the past decade suggests that global temperature will rise significantly in the next few years as the tropics moves inevitably to the next El Nino phase.
JC comments: Perhaps ‘standstill’ is a euphemism for ‘pause’, but recall all the flack that David Rose received a few months ago for writing about the ‘pause’. It is good to see Hansen paying more attention to unforced variability.
However Hansen’s simplistic reasoning about what can be expected in the next decade is, well, simplistic. GWPF reports on the latest decadal simulation from the UKMO, which predicts basically no warming for the next 5 years. Should we believe the UKMO model prediction? Well, I have more confidence in the UKMO prediction than in Hansen’s back of the envelope reasoning.
JC’s ‘forecast’ for the next 5 years: It looks like the AMO may have peaked, and we remain in the cool phase of the PDO with a predominance of La Nina events expected (unlikely to see a return to do El Nino dominance in the next decade). I predict we will see continuation of the ‘standstill’ in global average temperature for the next decade, with solar playing a role in this as well.
It also looks like black carbon is looming as more important than previously believed, see article at WUWT.