The Global Warming Challenge

Evidence-based forecasting for climate change

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February 2018 temperatures same as 11 years ago

without comments

The UAH global temperature anomaly for February 2018 was 0.20°C, which is little different from the February 2007 figure of 0.19°C, and lower than January and March 2007 figure of 0.43°C and 0.26°C. The updated chart for the extended (20 year) Climate Bet is at right. Click on the thumbnail chart for a larger image.

Some critics of our recent analysis of the Climate Bet at 10 years argued that temperatures were clearly higher at the end of the Bet period than they were at the beginning. Professor Armstrong’s side of the bet was the Green, Armstrong, and Soon (2009) no-change (no-trend) forecast. If the no-trend model of global mean temperatures is correct, there is a 50/50 chance that the temperature at the end of any period will be higher than at the beginning… and so comparing ending and starting observations is of no value in determining whether there is a dangerous trend, or not.

The Climate Bet instead compares cumulative absolute errors, which is the appropriate measure for assessing whether policy should be based on dangerous warming, or no change. To date, the cumulative absolute error of the dangerous warming forecasts of 3°C per century is nearly 15% larger than that of the no-change model forecasts

Other critics suggested that there was an upward trend over the bet period.  Trend lines can be fitted to random data… and, ex post, to series that cannot be forecast better than no-change. And people seek patterns. Given that preference, we will occasionally report on how the trend of the dangerous warming  projection and no trend compare with the ex post trend fitted to the global temperature data.

For the period of the Climate Bet to date, the ordinary least squares trend from the 2007 annual average Bet base year was 1.49°C per century; closer to no trend than to the dangerous warming forecasts of 3°C per century. But, as we discussed in our 10-year summary, squared errors are not relevant for policy decisions. The more policy-relevant least absolute deviation trend for the period, by contrast, was a much flatter and non-dangerous 1.17°C per century.

Kesten Green
12 March, 2017

Written by admin

March 12th, 2018 at 3:44 pm