Bjorn Lomborg, to make up for losing his $4million funding from the Australian government has just published a paper on the impact of current climate proposals. Possibly he’s also trying to improve his h-index, but given the Impact Factor of the Journal in which he’s published, it could take a while.
A suitable sub-title for Bjorn’s paper is probably: if you assume the worst, the worst will happen. The bottom line from his paper appears to be that in the most optimistic scenario, we will only reduce warming – relative to RCP8.5 – by 0.17oC. He appears to be selling this as an illustration of just how ineffective the Intended Nationally Determined Contributions (INDC) will be.
So, does he have a point? Well, no, and Joe Romm has largely pointed out why. Lomborg has essentially ignored China. China has pledged to peak its emissions by 2030, and yet Lomborg assumes that China’s emissions continue increasing until 2100 (his Figure 9). Furthermore, the difference between his most optimistic and his most pessimistic scenario is very small. Also, he assumes that in almost all cases the most optimistic scenario beyond 2030 is increasing emissions.
In fact, some of his assumptions just seem utterly bizarre. Somehow he thinks we will reduce emissions until 2030, and then start increasing them again. Well, sure, if we do that then the difference between RCP8.5, and what we actually do, might be small, but that’s almost certainly not the intent. It’s well known that warming depends largely on total emissions. The goal of emission reductions is to reduce total emissions, not simply emissions until 2030. If he assumes that the most optimistic scenario is increased emissions beyond 2030 so that, overall, we’ll ultimately emit about as much – by 2100 – as RCP8.5, then of course we’ll warm about as much as RCP8.5.
However, there’s no reason why the most optimistic scenario is increasing emissions beyond 2030; in fact, I’d argue that that’s not an optimistic scenario, by definition. This post suggests we could keep cumulative emissions to about 1400 GtC by 2100 (and warming of around 2.8oC). There are others not quite as optimistic, but still suggest considerably less warming than RP8.5.
So, the bottom line seems to be that Lomborg has assumed that we’ll start increasing emissions beyond 2030 so that total emissions will be similar to that for RCP8.5, and hence that the emission reductions planned to 2030 are going to be ineffective. Well, sure, if we do increase emissions beyond 2030, then they certainly will be ineffective. However, this is certainly not the intent and even if they’re not going to be as effective as some might like, they’re almost certainly not going to be as ineffective as Lomborg suggests.