"Since my last foray into the field, there has been a significant loss of faith in the notion that emission cuts alone can stop us short of reaching the tipping points. There is an emerging debate—emerging into public view, at least; it has been raging inside the climate science community for some time—about which methods of direct human intervention into the workings of the climate system would be valid and safe and which would not—in other words, about geo-engineering or climate engineering."