"How Much Could the Temperature Rise by 2100?"
Realclimate.org has an important post correcting a flawed news article making the rounds on the blogosphere.
An Australian article claims, “The world’s top climate scientists have cut their worst-case forecast for global warming over the next 100 years.” This is based on a misreading of the draft Fourth Assessment Report of the U.N.’s Intergovernmental Panel on Climate Change (IPCC).
The article has confused the projected temperature rise from a doubling of preindustrial levels of carbon dioxide concentrations (the so-called “climate sensitivity”), which the draft report says is 2°-4.5°C, with the projected temperature rise from whatever level of carbon dioxide the world actually ends up with in 2100, which could be considerably above a doubling (or below–if we act soon).
As I have noted previously, confusion about future temperature rise is common. The issue is even more confused here because, as realclimate.org explained previously, the climate sensitivity doesn’t even include crucial feedbacks and vicious cycles in the carbon cycle that could further boost warming. And, of course, the report is only at a draft stage, so perhaps the media should wait until the report is filed early next year before reporting, or misreporting, its conclusions.
The numbers are, in any case, nothing to be sanguine about, since any sane society would want to do everything possible to avoid warming beyond 2°C.