David Roberts has a recent post that I’ve only just noticed called why zero is a better climate target than 2 degrees. The zero refers to net global emissions, not to temperature. The argument is essentially that

zero is a much more compelling and evocative goal than the longer-standing and better-established climate goal of limiting temperature rise to 2 degrees or less.

David Roberts is, of course, quite correct that if we want to stabilise temperatures we’ll have to aim to get emissions to zero. If this could be accepted and focused on, it may well be more effective than having some kind of warming target. On the other hand, when we get to zero emissions, and how we get there, are relevant. Getting to zero emissions slowly by, for example, 2100 will be very different to doing so raidly and getting there by the middle of the century.

Also, we can relate a warming target to an emission target. For example, as the figure on the right shows, if we were to start reducing emissions now, we would need to get to zero emissions by around 2080 if we want a 66% chance of limiting warming to 2oC. If we continue increasing our emissions for the next 5 years, it would then need to get to zero by around 2060. So, it would seem to me that even if we thought that having a zero emissions target would be more compelling than a warming target, we can’t ignore that there is a relationship between emissions and warming.

On the other hand, it seems to me that the issue isn’t really what sort of target we should be aiming for, it’s whether or not we’re really doing anything to actually achieve the target, however it’s described. Despite the strong rhetoric from the Paris meeting, we really don’t yet seem to be taking emission reductions particularly seriously. My view is probably similar to the view expressed at the end of the abstract of this paper (H/T Stoat)

These debates are moot, however, as the decisions that need to be taken now to limit warming to 1.5 or 2 °C are very similar. We need to agree how to start, not where to end mitigation.