Recently published(1) results from the most comprehensive, predictive computer modeling show that unless rapid and drastic actions are taken, global warming over the next century will be about twice as severe as previously estimated. Developed at the Massachusetts Institute of Technology (USA) Joint Program on the Science and Policy of Global Change, the MIT Integrated Global Systems Model includes economic activity and other human activities, and associated energy usage in different countries, in addition to the physical aspects of climate change utilized by other models.
As published in the May, 2009 issue of the American Meteorological Society’s Journal of Climate the latest projections from the model are a median probability (there is a 50% chance of the value being more, or less than the median) for a mean global surface warming of 5.2oC (9.2oF), with a 90% probability range of 3.5 to 7.4oC, by year 2100 if no global policy to reduce emissions is implemented. This new projection is in contrast to the 2.4oC value of previous studies and is well above the range of the highest (scenario AiFI) “best estimate” of 4.0oC of the IPCC 2007 Fourth Assessment Report(2).
There is no one single factor that accounts for the increase of estimated values, but rather the difference results from the inclusion of additional factors in the model such as economic data, emissions of soot, and cooling by 20th century volcanoes, and other model refinements. The MIT team has developed a so-called “roulette wheel” to provide a graphical illustration of the model projections. In no policies are implemented to reduce emission of greenhouse gases the wheel, which is divided into six temperature ranges shows that the probability for less than a 3oC (5oF) temperature increase by 2100 is less than 1%, while the probability of an mean surface temperature increase of over 7oC (15oF) is about 9%.
(http://globalchange.mit.edu/resources/gamble/no-policy.html)
The model was also used to project the global mean surface temperature if a fairly aggressive policy of emissions control, based on a restriction of a total, cumulative emission of 4.2 trillion metric tons of C02-equivalent, was in place. This policy limit is in accord with a stabilization of the atmospheric concentration of CO2 at 550 ppm (the current level is 380ppm) which is the Kyoto Protocol target and also assumes that the Protocol is implemented by 2010. In this case the projection for the median increase by 2100 drops to 2.3oC (4.2oF) and the probability for the mean global surface temperature increase of less than 3oC is 90%
(http://globalchange.mit.edu/resources/gamble/policy.html)
Computer models have proven to be an excellent predictive tool. However, it must be remembered that they are based on, and tested against, what has been observed in the past. And, while modern computer power enables the construction of extremely complex models, they can still only be simplistic estimates of the vast assemblage of the processes determining global climate change. It should also be noted, that as the various computer models have been refined over time, they have consistently projected an increase of global warming, when compared to their predecessors. The very nature of science is cautious and conservative. The predictions discussed here are cause for considerable alarm, and when taken in the context of such models invariably resulting in higher projections as they are improved these findings warrant extremely significant consideration.
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1.) Probabilistic Forecast for 21st Century Climate Based on Uncertainties in Emissions (without Policy) and Climate Parameters. 2009. Sokolov, A.P., P.H. Stone, C.E. Forest, R.G. Prinn, M.C. Sarofim, M. Webster, S. Paltsev, C.A. Schlosser, D. Kicklighter, S. Dutkiewicz, J. Reilly, C. Wang, B. Felzer, J. Melillo, H.D. Jacoby. Journal of Climate, Online first, doi: 10.1175/2009JCLI2863.1
2.) IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp.
