Forcasting is the heart of science. It is easy to convince yourself that you understand something until you must predict what will happen. It is hard to predict things even when you can repeat the experiment. You must be very careful when you are predicting events that cannot be repeated.
The Massachusetts Institute of Technology (MIT) sponsors a Joint Program on the Science and Policy of Global Change. It released a report last month: "Probabilistic Forecast for 21st Century Climate based on uncertainties in emissions (without policy) and climate parameters."
Green and Armstrong examined this report. They found serious problems in trusting the MIT results, related to proper forcasting methods and skepticism. A forcast of "climate change" may seem to fit the data, until you find out that "no change" fits the data better.
[edited] The MIT authors predicted that global warming could be twice as severe as previously forecast, and more severe than the official projections of the UN Intergovernmental Panel on Climate Change (IPCC). Their prediction is based in part on 400 runs of a computer model of climate and economic activity. So, they recommend massive government action.
The MIT group espouses lofty objectives based on "independent policy analysis and public education in global environmental change". But, we found they violated 49 important forcasting principles. For such an important problem, they should not have violated even one.
So what's really wrong with their report? Their phrase "global environmental change" provides a clue. The group implicitly rejects the possibility of no or unimportant change, or the possibility of unpredictable change.
A forecast of "no-change" can be hard to beat in many circumstances. No-change can be appropriate even when a great deal of change is possible, but the direction, extent, or duration is uncertain.
Earth's temperature has gone up and down irregularly over periods from one year to thousands of years. Moreover, science has not been able to tell us why. There is much uncertainty about past climate changes and about the strength and even direction of causal relationships.
Do warming temperatures result in more carbon dioxide in the atmosphere, or is it the other way around, or a bit of both? Does warming of the atmosphere result in negative or positive feedback from clouds? There are many more such questions without answers. All this strongly suggests that a no-change forecast is the appropriate long-term forecast.
We compared the IPCC projection of 0.03 C temperature increase per year with what actually happened from 1850 to 2007. The errors from the IPCC prediction were 12 times larger than the errors of the no-change prediction.
The forecasts from the MIT modellers and from the IPCC are merely the opinions of some scientists and computer modellers. These are not truly scientific forecasts.
Dr. Kesten C. Green is a senior research fellow of the Business and Economic Forecasting Unit at Monash University, Australia.
Dr. J. Scott Armstrong is Professor of Marketing at The Wharton School, University of Pennsylvania.
They are co-directors of the public service Web site Forecasting Principles sponsored by the International Institute of Forecasters.
Dispelling the Global Warming Myth
There is a very close match between global temperature and solar output. See the graph. That even seems reasonable in its own way. (smile)
AGW Scientists Can't Predict
Academic degrees mean nothing if you can't say what is going to happen. Watch out for global warming scientists who can't predict the details. And watch out for "economists" who fiddle some equation as a reason to take your money to improve your life.