Come on, Matt Ridley, it’s not that difficult

Matt Ridley has a new article in The Times, called Spare me the selfishness of the eco-toffs. I appreciate that Matt Ridley may not have chosen the title, but I suspect I’m not alone in finding an article criticising eco-toffs, written by a Viscount, a little ironic. The Times article is paywalled, but it appears that the full article is here.

I’ve been rather critical of Matt Ridley in the past, so will keep this short. In all honesty, I’d be quite keen if Matt Ridley actually stopped making the kinds of silly mistakes he seems to make. He clearly has a voice and I’d rather that what he said was credible, rather than nonsensical. I guess that may, however, weaken his preferred narrative, and so I probably shouldn’t hold my breath.

In this most recent article Matt Ridley focuses on the newly released IPCC report. I thought I might highlight a couple of aspects of what Matt Ridley has said that seem to indicate a very significant misunderstanding of what the report is really saying. One thing he mentions is

But when you cut through the spin, what the IPCC is actually saying is that there is a range of possibilities, from no net harm at all (scenario RCP2.6) through two middling scenarios to one where gathering harm from mid century culminates in potentially dire consequences by 2100 (scenario RCP8.5).

Let’s make something very clear. The RCP’s are Representative Concentration Pathways. They are simply four possible future anthropogenic greenhouse gas emission pathways. They’re meant to bracket the range of possible emission pathways. We’ll almost certainly not exactly follow one of these particular pathways. They’re also not possible in some kind of probabilistic sense; we’re not going to randomly follow one of these pathways. Ignoring major changes in the carbon cycle, we get to decide which of these pathways we want to follow.

Of course, if we do follow a low emission pathway, the resulting warming will be lower than if we follow a high emission pathway. That’s kind of the point. We’re meant to consider the range of warming associated with each emission pathway and use that to inform policy. Implying that we may, by chance, follow a low emission pathway seems nonsensical. I guess it is possible that something magical will happen in the coming decades, that will allow us to switch easily from fossil fuels to some other energy source. I’d argue, though, that that is more likely if we actual try to do so, than if we simply hope that we’ll do so.

Matt Ridley goes on to say

So let’s focus on the two middle scenarios, known as RCP4.5 and RCP6. In these more realistic projections, if you use the latest and best estimates of the climate’s “sensitivity” to carbon dioxide (somewhat lower than the out-of-date ones still used by the IPCC), the most probable outcome is that world will be respectively just 0.8 and 1.2 degrees Celsius warmer than today by the last two decades of this century.

Firstly, his latest and best estimates of climate sensitivity largely refers to the results from energy budget estimates preferred by Nic Lewis (and some others). Although there is nothing fundamentally wrong with these estimates, there are reasons why they might be regarded as lower limits, rather than somehow more accurate than other methods. Also out-of-date is Matt Ridley’s own construct, not a view held by actual experts.

Matt Ridley is actually correct that if his preferred estimates are correct, then the best estimate from these methods would suggest about 1.2^oC by 2100 (relative to today). However, you shouldn’t really consider what Matt Ridley calls the best estimate a particularly likely outcome. Typically it’s the median of the distribution, which means that there is a 50% chance that the actual value will be higher/lower than this best estimate. Therefore, even his preferred method suggest that we could have between 0.9 and 2.9^oC of warming, relative to today for RCP6.0 (or, about between 2^oC and 4^cC relative to pre-industrial times).

So, even using Matt Ridley’s preferred method (which suggests a lower climate sensitivity than other methods) we’re almost guaranteed – if we follow an RCP6.0 emissions pathway – to have more than 2^oc of warming by 2100. Maybe Matt Ridley thinks differently to me (I really hope so) but climate policy isn’t some kind of bet; we aren’t gambling on a precise value for climate sensitivity. Climate policy should, in my view, be some kind of risk analysis. How do we balance minimising the risks associated with climate change, with the risks/costs associated with minimising these risks? Choosing to follow an emissions pathway that is almost certain to result in more than 2^oC of warming, doesn’t seem particularly sensible.

I must admit, that I’m starting to tire of critiquing things that people like Matt Ridley say. They seem quite comfortable repeating this type of stuff despite people regularly pointing out their errors. If Matt Ridley really thinks that we shouldn’t be too concerned about following an RCP6.0 emissions pathway, maybe he could at least acknowledge that this could lead to much more warming than his articles suggest. If he can’t, or won’t, do this, then I would argue he’s neither rational nor honest.