a median probability of surface warming of 5.2 degrees Celsius by 2100, with a 90% probability range of 3.5 to 7.4 degrees. This can be compared to a median projected increase in the 2003 study of just 2.4 degrees. The difference is caused by several factors rather than any single big change. Among these are improved economic modeling and newer economic data showing less chance of low emissions than had been projected in the earlier scenarios. Other changes include accounting for the past masking of underlying warming by the cooling induced by 20th century volcanoes, and for emissions of soot, which can add to the warming effect. In addition, measurements of deep ocean temperature rises, which enable estimates of how fast heat and carbon dioxide are removed from the atmosphere and transferred to the ocean depths, imply lower transfer rates than previously estimated.
It goes on to say:
And the odds indicated by this modeling may actually understate the problem, because the model does not fully incorporate other positive feedbacks that can occur, for example, if increased temperatures caused a large-scale melting of permafrost in arctic regions and subsequent release of large quantities of methane, a very potent greenhouse gas. Including that feedback "is just going to make it worse," Prinn says.In short, the scientists admit that they have underestimated how bad global warming is going to get, and that their best estimate to date, has a high probability of also underestimating the rise in temperatures.
This should come as no surprise to anyone who's followed the discussion on global warming. Consistently, and without fail, scientists have found that previous estimates have always been overly optimistic. It should be further noted that simply cutting the level of greenhouse gas emissions is not going to be enough to reverse the changes. For that to occur, radical carbon negative policies are going to have to be introduced, of which there has been little to no discussion, so far as I am aware.
For those of us on Earth, this means that we can expect more aggressive efforts to try and limit the level of greenhouse gas emissions. It also has implications for the terraforming of Mars as well. Given that the warming effects of CO2 appear to be stronger than previously believed, it seems reasonable to conclude that the estimates of the amount of time needed to begin the warming of Mars are equally wrong.
While some might argue that we shouldn't begin tampering with the Martian atmosphere until we better understand our own, "playing" with the Martian atmosphere now gives us a controlled environment in which we can better understand how CO2 affects planetary conditions, with fewer variables to try and account for.