Up to now it has been generally assumed that global warming will be a linear process. However evidence from the geological past linked with climate modelling that takes into account the global warming that is already locked into the system indicates that there may not be a linear response to rising CO2 levels. There is a danger that at some point we will cross a threshhold when global warming accelerates. By continuing to increase the amount of CO2 in the atmosphere we are getting closer to that point.

President George W. Bush once famously declared: "I'm the decider, and I decide what's best." But when it comes to environmental issues, especially global warming, Bush often sounds more like the dissembler than the decider.