I haven’t really had much to say, hence the lack of posts. I still don’t, but I thought I would quickly highlight a recent paper by Xu and Ramanathan called Well below 2 °C: Mitigation strategies for avoiding dangerous to catastrophic climate changes. I haven’t really had a chance to read it as thoroughly as I should, but it’s open access (I think) so, if you’re interested, I’d encourage you to read it. It partly caught my eye because it uses terms like dangerous, catastrophic and even existential threat. Partly, these are their own definitions; > 1.5oC defined as dangerous, > 3oC defined as catastrophic, and > 5oC potentially being an existential threat. It also tries to take various uncertainties into account (such as carbon cycle feedbacks).I didn’t want to say too much, but did want to post the figure on the right. It shows the range of warming in the two different scenarios that they regard as not including climate policies (essentially RCP6 and RCP8.5) and a well-below 2C scenario (WB2C). This is what I wanted to highlight. Even the well-below 2C scenario has a roughly one-third chance of exceeding 2oC, and a non-negligible change of exceeding 3oC.
If you consider the table in this Carbon Brief article then a 66% chance of staying below 2oC would require emitting no more than another 1000GtCO2 (272GtC) from 2011. We’ve already emitted about 60GtC since 2011, so we have about 200 GtC left. In other words, another 20 years at current emissions would use up this carbon budget. Alternatively, we have to start reducing emissions pretty soon if we want to still have a 66% chance of keeping warming below 2oC. However, even if we do meet this carbon budget target, we would still have a one-third chance of exceeding 2oC and a few percent chance of exceeding 3oC.
I find this rather sobering and am not quite sure how to wrap this up. I don’t think we should focus on the possibility that everything could be much worse than we hope. However, I also don’t think we should ignore this either. What this means to me is that we should start taking this seriously, because ultimately we will need to get net emissions to zero and the sooner we start thinking of ways to do this, the less likely it will be that the outcome will be something that we would rather have avoided.