Steve Koonin has an Op-Ed in the New York Times called The tough realities of the Paris climate talks. It’s a little odd, in that when I last discussed Steve Koonin he appeared to be suggesting that the effect of climate change would be small. Andy Lacis wrote a fantastic response. Now he seems to be arguing that there is little we can, or should, do.
His basic premise is that there are two scientific realities that should guide our decisions. Firstly, he says,
The first reality is that emissions of carbon dioxide, the greenhouse gas of greatest concern, accumulate in the atmosphere and remain there for centuries as they are slowly absorbed by plants and the oceans.
Okay, yes, I’ve written about this quite extensively myself. However, he then seems to conclude that because the planned reductions are so small, that they’re really not worth bothering with. However, the long-term atmospheric concentration depends on how much we emit in total. The less we emit, the lower it will be. Arguing that we can’t – or aren’t able to – do much, therefore we shouldn’t do anything, seems remarkably weak. If anything it might suggest that we should do more, not less.
The second scientific reality, arising from peculiarities of the carbon dioxide molecule, is that the warming influence of the gas in the atmosphere changes less than proportionately as the concentration changes. As a result, small reductions will have progressively less influence on the climate as the atmospheric concentration increases.
Now this is partly true, but also a little misleading. It’s true that the change in forcing depends logarithmically on concentration. However, the change in concentration does not depend linearly on emissions. A bigger fraction of our emissions are likely to remain in the atmosphere as we emit more and more. For example, the figure on the right shows that concentrations will increase by about 200ppm if we emit 3000GtCO2. If, however, we emit a further 3000GtCO2, it produces an increase in concentration of about 300ppm. So, in fact, the warming is expected to depend linearly on total emissions, even though it depends logarithmically on concentrations. On average, the impact of a reduction in emissions will be the same now as it probably will be in the future.
Additionally, given that the initial drawdown of our emissions is quite fast, it turns out that the peak warming from a particular emission occurs relatively quickly (decade or so). So, any reduction in emissons can have an impact on a relatively short timescale. Of course, this could be masked by variability, but the idea that we shouldn’t reduce emissions now because it won’t have any impact on the short-term is wrong.
I don’t know if there is really anything else to say about his article. His first scientific reality is essentially right, but does not obviously lead to the conclusion that we shouldn’t bother reducing our emissions; many would argue that if a reasonable fraction of our emissions will stay in the atmosphere for millenia (as is indeed expected) we should put more – not less – effort into reducing them than we currently are. In fact, part of his first scientific reality, isn’t a scientific reality at all. The scientific aspect of his first scientific reality is right (a reasonable fraction of our emissions will stay in the atmosphere for millenia), but our ability, or lack thereof, to reduce emissions is not a scientific reality, but – at best – a societal reality. There’s no scientific reason why we can’t do so.
His second scientific reality is a little muddled; warming may depend logarithmically on concentration, but it is expected to depend linearly on emissions. If we emit, in total, 10% less, we will – on average – warm by 10% less. So, the idea that future emissions will have ever decreasing impact is simply wrong. What I will say about the rest of his Op-Ed is that it is essentially an argument in favour of adapting, rather than mitigating. Apparently we can adapt to almost anything, apart from a world in which we try to reduce emissions of CO2 into the atmosphere.