…was the basis for Paul Krugman’s “deniers are treasonous” rant in the NYT.  The Financial Post of Canada asked Kesten C. Green And J. Scott Armstrong, respected academics, to review MIT’s work.

When we drive on a long bridge over a river or fly in a passenger aircraft, we expect the bridge and the plane to have been designed and built in ways that are consistent with proven scientific principles. Should we expect similar standards to apply to forecasts that are intended to help policymakers make important decisions that will affect people’s jobs and even their lives? Of course we should. Such standards exist. But are they being followed?

The Financial Post asked us to look at a report last month from the Massachusetts Institute of Technology (MIT) Joint Program on the Science and Policy of Global Change, titled “Probabilistic Forecast for 21st Century Climate based on uncertainties in emissions (without policy) and climate parameters.”

The MIT report authors predicted that, without massive government action, global warming could be twice as severe as previously forecast, and more severe than the official projections of the United Nations’ Intergovernmental Panel on Climate Change (IPCC). The MIT authors said their report is based in part on 400 runs of a computer model of the global climate and economic activity.

While the MIT group espouses lofty-sounding objectives to provide leadership with “independent policy analysis and public education in global environmental change,” we found their procedures inconsistent with important forecasting principles. No more than 30% of forecasting principles were properly applied by the MIT modellers and 49 principles were violated. For an important problem such as this, we do not think it is defensible to violate a single principle.

For example, MIT forecasters should have shrunk forecasts of change in the face of uncertainty about predictions of the explanatory variables; in this case the variables postulated to influence temperatures. More generally, they should also have been conservative in this situation of high uncertainty and instability. They were not.

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