New Scientist: IT IS all downhill from here on. Right now Earth's climate is not warming too much when extra carbon dioxide reaches the atmosphere, but as levels of the gas keep rising, the climate will become ever more sensitive to it. That means emissions in 2100 could be even more dangerous than emissions today. Despite decades of research, nobody is really sure how sensitive the climate is to carbon dioxide. Our best guess, according to the most recent Intergovernmental Panel on Climate Change report, is that...