The IPCC now talks in terms of carbon budgets – how much CO2 we can emit before temperatures are 2C higher. Because CO2 remains in the atmosphere for hundreds of years this is pretty well a fixed number – 1000 Giga tonnes of carbon. We’ve already emitted most of that. To stay below 1000Gt, and thus below a 2C temperature increase, we need to reduce emissions. Yet, today, they’re increasing at 1.8% per annum.
The longer we wait to start reduction, the more aggressive we’ll have to be. And, if we do not decrease, we’re out of runway by mid-century; the rise will be more than 2C – with attendant more extreme weather variations, sea level rise, etc. More CO2 means higher temperatures.
This is not exactly mind-blowing stuff. The international goal is no more than a 2C rise. That means no more than 1000Gt of carbon. Carrying on as we are we blow the limit in a few decades. All Stocker is doing is pointing out the bleeding obvious, based upon the very conservative science of the IPCC.
But if you’re a so-called climate sceptic you decry the arithmetic as some bizarre form of activism. Eh?