Global mean surface temperature fluctuations & trends 1891-2015 & forecasts a year ahead 2000-2019
Prof Chris Folland, UK Met Office
The talk will present a recently published analysis of the causes of fluctuations and trends in global mean surface temperature (land and ocean surface, GST) from 1891-2015 using an observational analysis informed by a range of model results. Also included is a comparison with the mean of CMIP5 model reconstructions of GST.
Firstly, I briefly review other observational and model analyses of GST over the instrumental period in the context of global climate change. The main part of the talk shows how observed GST can be divided into five sections, each exhibiting little or considerable warming. The analysis identifies the main external and internal forcing factors that explain this very variable behaviour down to some multi-month time scales. A key finding is that in the most recent period of relatively little warming, 1998-2013, often called the “pause” or “hiatus”, solar variability explains an important part of GST variability. This is in addition to a combination of the El Niño, La Niña and the Interdecadal Pacific Oscillation identified elsewhere. Two periods with likely deficiencies in observed sea surface temperatures are also highlighted, an area of ongoing international research. The talk finishes with a brief review of the high skill of 20 closely related real-time forecasts of GST a year ahead, issued from 2000-2019. Overall, the talk concludes that nearly all overall warming of GST since 1891 is due to increased forcing from greenhouse gases partially offset by increasing anthropogenic aerosols.
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