Over-egging that climate change pudding

This seems rather alarmist:

Without urgent action to accelerate decarbonisation, remove carbon from the atmosphere and repair nature, the plausible worst-case hit to global economies would be 50% in the two decades before 2090, the IFoA report said.

Ah, no, that’s just the journalists at The Guardian having their usual problem with numbers:

Global economic growth could plummet by 50% between 2070 and 2090 from the catastrophic shocks of climate change unless immediate action by political leaders is taken to decarbonise and restore nature, according to a new report.

It is the rate of growth which could fall, not the economy itself.

Which, you know, is fine. For as all the right-on do say these days - degrowth and all that - economic growth is just so passe these days. We don’t need it, don’t want it and can’t have it anyway. So, that’s good then.

But where does this estimate come from? What is assumed to give us this?

The Network for Greening the Financial System (NGFS) provides analysis of a range of estimates for the negative GDP impact of climate change under a current policies scenario of 3°C of warming by 2100. These range from 2% GDP (Nordhaus & Boyer) impact to 44% GDP (Bilal & Känzig) impact by 2100.10 Alternative methodologies provide wider ranges still: up to 63%. What is important to understand is that these results are the output of complex models, which are highly dependent on the methodologies used for calculations and assumptions. A prudent approach would be to take the highest estimate of economic loss and reduce it when evidence becomes available that it is over-stated, rather than the other way round.

So we’ll add in everything that shrieking hysteria can possibly think of that might go wrong, nothing at all that might go right and our estimate of the very worst that can happen is that, in 50 years time, the rate of growth - not the size of GDP, the rate of growth of it - could halve?

Oh. Right. Seems, umm, manageable?

Further, even if it’s correct (it isn’t, as with James Hansen and his estimation that the correct carbon tax is $1,000 a tonne CO2-e. No, that’s “it could be as high as that” and that should be weighted by probability against the other possible costs and outcomes, as here) then that just takes us back into Stern Review and William Nordhaus territory. It’s worth killing how much economic growth now through panicked reactions to avoid losing 50% of economic growth in 50 years time?

Even with low discount rates the answer is, well, not much acshully.

Tim Worstall