Bad climate science is still just bad science

That doesn’t stop people doing it of course. From Sir David King, former chief scientific advisor to the UK Government, now at CCAG:

Recent analysis shows that annual global GDP costs due to extreme weather events could rise towards 100% of global GDP around the end of the century.

Therefore we must do everything to avoid climate change, right?

It’s that second part that isn’t correct. The warning is drawn from this report to actuaries.

A relatively simple log damage function could be used that assumes 100% GDP loss at a certain level of warming, say 6˚C, 5˚C, or 4˚C, although some may argue that even 3˚C would be extremely challenging to adapt to, and certainly sensitivities should be undertaken at all of these.

That’s the 100% mention - we should model, as an outlier, that this might be true. Which is entirely and wholly different from a statement that damages will be that much.

It’s also not what some will think, that the entirety of the economy - a 100% loss - will disappear and so we all die. Aiee.

It is, instead, that climate change will reduce the size of the global economy in 2100 by about the size of the global economy today. We are talking of GDP then being reduced by 100% of GDP now. Which is indeed an entirely different statement.

For we also have to think about economic policy between now and 2100 and how much that will influence the growth of the global economy. Which has, in fact, been done, in the SRES, that report on economic models and climate change from the 1990s. In which we are told that globalised free market capitalism (A1) will lead to an economy 11 times larger in 2100 than in 1990. Or, a regionalised, more socially democratic system (B2) about 5.5 times larger.

Which economic system we use for a century has far more impact on the final size of the economy than climate change or not climate change that is.

Good science is about balancing those two gains and losses to produce the best overall outcome. Don’t, for example, use bad economic policy to avoid climate change damages where that bad economic policy produces more loss of GDP than the climate change damage does.

A balancing act which has also been done in that very SRES. A1FI (where we run out of conventional fossil fuels, don’t frack and so turn back to coal) has high climate damage costs. A1T (where we still use globalised free market capitalism but also move to fossil free energy generation) produces low heating, thus low climate change damages and also the highest GDP of the modelling set.

Another way to approach the same point. Sure, OK, Greenland melting will produce loss of potential GDP in the future. Now, these policies being recommended - how much potential GDP loss will they cause? The correct - economic - answer is, of course, whatever set of policies produce, on balance, the highest final GDP number.

As the IPCC’s own modelling shows, that’s globalised free market capitalism along with the transition away from fossil fuels.

OK. Sounds like a plan to us. So why are scientists not saying so?