The Massachusetts Institute of Technology Joint Program on the Science and Policy of Climate Change has joined the climate realists. The realists are the growing group of scientists who understand that the business as usual emissions path leads to unmitigated catastrophe (see, for instance, “Hadley Center: “Catastrophic” 5-7°C warming by 2100 on current emissions path” and below).
The Program issued a remarkable, though little-remarked-on, report in January, “Probabilistic Forecast for 21st Century Climate Based on Uncertainties in Emissions (without Policy) and Climate Parameters,” by over a dozen leading experts. They reanalyzed their model’s 2003 projections model using the latest data, and concluded:
The MIT Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model’s first projections were published in 2003 substantial improvements have been made to the model and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections, e.g., the median surface warming in 2091 to 2100 is 5.1°C compared to 2.4°C in the earlier study.
[Note: That rise is compared to 1990 levels. So you can add at least 0.5 °C and 1.0 °F for comparison with pre-industrial temperatures.]
Their median projection for the atmospheric concentration of carbon dioxide in 2095 is a jaw-dropping 866 ppm.
Projected decadal mean concentrations of CO2. Red solid lines are median, 5% and 95% percentiles for present study: dashed blue line the same from their 2003 projection.
Why the change? The Program’s website explains: