Ted Nordhaus, of Breakthrough Institute fame, has a recent article in Foreign Affairs called [t]he two-degree delusion. Basically, it argues that we cannot possibly achieve this target without harming the poor, and that continuing to try and do so also makes it more difficult to focus on viable alternatives (adaptation, for example).
There’s a great deal one could say about Ted Nordhaus’s arguments, but there was one thing that I wanted to highlight, that I think he gets largely wrong. He says:
Such calculations are further complicated by the substantial lag between when we emit carbon and when we experience the climate impacts of doing so: because of the time lag, and because of the substantial amount of carbon already emitted (atmospheric concentrations of carbon today stand at 407 parts per million, versus 275 prior to the start of the Industrial Revolution), even an extreme precautionary approach that ended all greenhouse gas emissions immediately would not much affect the trajectory of global temperatures or climate impacts until late in this century at the earliest.
the median time between an emission and maximum warming is 10.1 years, with a 90% probability range of 6.6–30.7 years.
In a sense the issue is that there is a difference between stabilising emissions, stabilising concentrations, and halting emissions. If we stabilise emissions, concentrations will continue to rise, and we will continue to warm. Stabilising concentrations will require – on decadal timescales, at least – substantial emission reductions and will lead to continued warming for many decades. This is because of the inertia in the climate system.
If, however, we actually halt emissions, then there may be little in the way of committed warming. Also, see this Realclimate post. It does depend somewhat on the mixture of long-lived greenhouse gases (GHGs), short-lived GHGs, and aerosols, but it’s not true that what we do now will have no impact until late this century, at the earliest. In many respects, the inertia is really societal, not climatic.
As for the 2C target itself; yes, it does seem likely that we will not keep warming below 2C. Current emission reduction committments will probably only keep us below 3.5C. I also agree that we should be willing to consider the implications of attempts to drastically reduce emissions. However, I still think there are reasons for maintaining something like a 2C target; even if we do miss it, there’s likely to be a vast difference between just missing it, and missing it by a lot.
Also, if people are concerned about the impact of trying to reduce emissions now so as to potentially keep warming below 2C, they might want to also consider what would happen if we do not try to reduce emissions now and then discover that the climate impacts are a severe as some people expect. We’d either then have to accept further warming with even more severe impacts emerging, or we’d have to plan for even more drastic emission reductions than would be required today. This would also not reverse the changes that had already occurred; without some kind of technological intervention, climate change is likely irreversible on human timescales.