I guess the big news at the moment, which is almost old news now, is the IPCC’s Special Report on Global Warming of 1.5oC. I’m not even all that sure what to say about it. It’s not presenting anything wildly surprising. It does make clear that if we limit warming to 1.5oC then the impacts will be less severe than if we only limit it to 2oC. It also discusses the impacts on ecosystems, which is something that I would like to understand better. Carbon Brief has an in-depth Q&A on the Special Report.
What I did like is that it stressed that our emissions to date have probably not yet committed us to 1.5oC of warming. I’ve written about our committed warming a number of times before and I do think it’s an important issue that is not all that well understood. It’s often claimed that we are committed to a further warming because the large heat capacity of the oceans means that we haven’t reached the equilibrium temperature for our current atmospheric CO2 concentration.
However, if (when) we get emissions to zero, the oceans will take up CO2 so that temperatures will roughly stabilise, and the relevant temperature is more the transient response to the atmospheric concentration when emissions cease, than the equilibrium response. There are some complications related to aerosols and short-lived greenhouse gases, which I discuss in this post and which is discussed in the IPCC’s Special Report, but this is roughly correct.
This is also the basis for the carbon budget approach; ultimately our overall warming depends largely on how much we emit. The new Special Report estimates the remaining carbon budget if we wish to limit warming to 1.5oC. It suggests a slightly larger remaining carbon budget than was suggested by the IPCC’s AR5 report. Zeke Hausfather has a really nice Carbon Brief article that discusses this.
This issue of the carbon budget is where the value of the IPCC Special Report becomes unclear. There is a range for the remaining carbon budget, but it’s about 420GtCO2 (i.e., this is roughly how much we can emit from now if we want a reasonable chance of limiting warming to 1.5oC). However, we’re currently emitting about 42GtCO2 per year. Hence, keeping warming below 1.5oC means that we can emit no more than about 10 years of current emissions. Even if you’re wildly optimistic, this seems highly unrealistic.
On the other hand, the remaining carbon budget if we want to limit warming to 2oC is not significantly greater. So, in some sense, what we would need to do now is not all that strongly dependent on our target (well, unless the target is to simply do nothing). We would need to start finding ways to reduce our emissions. My own view is that we can worry about how fast, once we’ve worked out how to start. My suspicion (which could be wrong) is that once we work out how to start reducing emissions, we might actually find it reasonably straight-forward to make substantial reductions. It may well be difficult to actually get it to zero, but we do have some time to work that out.
Okay, I will admit that the above is all a bit vague. I don’t have any specific ideas as to how we might actually start reducing our emissions. My view is becoming that we need a whole range of things. A price on carbon, investment in technology development, incentivising lower carbon lifestyles, etc. I still think that one of the big problems is that there are still many, in particular those in leadership roles, who do not really see the need to do anything. It’s hard to see how we can get started while many think there’s no reason to do so. I don’t have any good ideas as to how to engage such people and convince them that there are benefits to acting to reduce our emissions, but I do think it’s important to try and do so. More about that in another post, maybe.
In-depth Q&A: The IPCC’s Special Report on Climate Change at 1.5C (Carbon Brief).
Why the IPCC 1.5C report expanded the carbon budget (Carbon Brief).
Posts on committed warming.