The 2C fantasy?

In the run up to the Paris meeting there seem to be a number of people focusing on the idea that the 2^oC limit is essentially now a fantasy. There’s a post by Andy Revkin, and there’s a Nature feature called is the 2^oC world a fantasy.

My own view is that giving ourselves a good chance of keeping warming below 2^oC will be difficult. To have something like a 66% chance of staying below 2^oC would require emitting no more than about another 300GtC. At the current rate, this could take less than another 30 years. So, clearly not an easy task. However, that doesn’t mean that it’s impossible, or that there aren’t ways that it could be achieved. So, I find how many seem to frame this issue very frustrating.

Consider the Nature feature. It says

Climate modellers have developed dozens of rosy 2^oC scenarios over several years,

Why rosy? They are simply models that give some indication of what pathways we could follow to give some kind of chance of staying below 2^oC.

Followed by:

This work has fuelled hope among policymakers and environ­mentalists

How? I don’t think anyone who is moderately numerate fails to understand that trying to limit total future emissions to something like 300GtC is not going to be easy. What are they meant to do? Give in to despair?

And:

But take a closer look, some scientists argue, and the 2^oC scenarios that define that path seem so optimistic and detached from current political realities that they verge on the farcical.

This is one of the statements that really bugs me. In what sense are they meant to put political reality into a climate model? What would happen if climate scientists suddenly made such judgements? It just seems ridiculous. Climate models fundamentally obey the laws of physics. Until such time as something is physically impossible, it is still possible. The decision as to whether or not it is possible in a societally relevant sense is a decision that should be made by policy makers who are – ideally – acting on behalf of society.

The Nature feature also quotes Oliver Geden (who is also quoted by Andy Revkin) who says

Everybody is sort of underwriting the 2-degree cheque, but scientists have to think about the credibility of climate science.

How has this got anything to do with the credibility of climate science? Climate scientists are simply presenting possible future pathways. Imagine the uproar if a bunch of climate scientists were suddenly to say “sorry, although this pathway is actually possible, we’ve decided that we should no longer consider it because it is a political impossibility”. If anything, it seems that doing as Geden seems to be suggesting would be introducing politics directly into climate science, and damaging their goal of being policy relevant without being policy prescriptive.

There also seems to be a rather bizarre suggestion that somehow these supposedly optimistic scenarios are allowing us to carry on as we are, because they imply we can fix things later. For example

Models that have these negative emissions really do let you continue to party on now, because you have these options later

But these models aren’t – as far as I’m aware – suggesting that we can invoke negative emissions later. They’re models that suggest that there are certain emission pathways that may require negative emissions if we wish to still keep below 2^oC. If this is not likely to be possible, then surely – if we still think aiming to stay below 2^oC is a sensible target – we should then be aiming to follow some other kind of emission pathway that doesn’t require negative emissions, not blaming scientists for presenting future pathways that you think might be impossible to follow. Surely this isn’t all that hard to understand?

I guess at the end of the day, I find these kind of argument disingenuous. There seems to be two basic ways to look at this. Either you think a 2^oC target is what we should be aiming for. If so, then what the climate models are suggesting is that we have to substantially reduce our emissions and we should probably start doing so now. Remember, there are large uncertainties. The roughly 300GtC carbon budget is based on giving us something like a 66% chance of staying below 2^oC. Consequently, emitting more than 300GtC does not mean that we will fail to do so. We still might, and if someone thinks that a 2^oC target is worth aiming for, then just missing it is likely to be a good deal better than giving up altogether.

An alternative is to disagree with there being some kind of 2^oC target and – consequently – to argue for something different. Maybe a higher target, or some kind of different strategy that doesn’t directly involve a target. However, trying to blame scientists for presenting pathways that you now regard as politically impossible, just seems to entirely miss the point – intentionally, in some cases, I think. If we do miss what is regarded as an important target, it’s not going to be the fault of the scientists who have been highlighting various possible future pathways and outcomes. I fail to see how criticising climate scientists is anything other than trying to find a scapegoat for our lack of willingness to actually get down and do something constructive…well, or an excuse to continue doing nothing.