His calculations are to be published in the science journal Nature. The amount of carbon dioxide in the air is a crucial parameter. “We found that the levels of CO2 which we could quite likely reach during this century are sufficient to produce that amount of warming,” he said. “Presuming the calculations are right, that it is going to happen, and that we are in the right ballpark, then you would prevent it (the meltdown) happening by not allowing CO2 to go above the levels we were considering,” Gregory said.
The lowest CO2 concentration scenario used in the models was 450 parts per million. Current levels are below that, according to Gregory, but by the middle of this century are likely to exceed it.