The Massachusetts Institute of Technology Joint Program on the Science and Policy of Climate Change issued a report in January, “Probabilistic Forecast for 21st Century Climate Based on Uncertainties in Emissions (without Policy) and Climate Parameters”
They conclude that if we take no action to reduce greenhouse gas emissions, "the median surface warming in 2091 to 2100 is 5.1°C...there is now a nine percent chance (about one in 11 odds) that the global average surface temperature would increase by more than 7°C (12.6°F) by the end of this century, compared with only a less than one percent chance (one in 100 odds) that warming would be limited to below 3°C (5.4°F)."
If we do take action, the MIT scientists find we can limit the warming over the 21st century to 2-3°C.
They had issued a similar report with more conservative warming estimates in 2003. 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.
The reason for this revision is that the carbon sinks are saturating, and the amplifying feedbacks are worse than previously thought. They also offer these nice Global Gamble Roulette Wheels.
