Bill McGuire and first derivatives

We admit that we can get confused about numbers - socks being taken off to count into double digits and all that. But we believe that this is called first derivatives.

A bloodcurdling piece in The Guardian detailing how climate change is about to come and broil us all in our beds by Bill McGuire:

If you think the temperature uncomfortable today, let me take you to the last day of July 2052, the rays of the climbing sun reveal a city still sweltering in the residual heat of the day before. From the air, London resembles a colossal refugee camp. Streets, gardens and parks are teeming with tents and cobbled-together shelters, within which the city’s residents have spent another uncomfortable night away from the heat traps that their houses and flats have become. After six days when the temperature peaked at about 40C, another scorcher is on the way.

Oh. Right. Presumably broiling in hell in this world as a result of sins against Gaia. Except:

While such measures will help to mitigate the worst, casting a shadow over our efforts will be the impact of a failing climate on the global economy, and the consequences for the UK – with a number of analyses forecasting significant reductions in global GDP by mid-century. Inevitably, this will translate into increased hardship for many UK citizens, compromising their ability to cope with the new conditions. At the same time, a seriously weakened national economy will leave government with less money to build the resilience the country needs to successfully prevail in a hotter world.

Ah. No. That is looking to the Institute of Actuaries report, the Guardian’s link is here. The URL gets this right in a way that the article doesn’t, for that URL says “economic growth could fall 50 over 20 years”. For that is what is being predicted. Not that GDP itself will fall by 50%, but that the rate of growth from now into the future will fall by 50%. It, absolutely, is not that Britain becomes poorer than it is now. It is that Britain will become poorer than it could have been without the effects of climate change. As we say, we believe this is the first derivative, something about the rate of growth not the actual position itself.

Because we read footnotes. From the IoA report:

For example, in The Emperor's New Climate Scenarios a methodology based on a technique known as reverse stress testing suggests to 'expect 50% GDP destruction – somewhere between 2070 and 2090'. 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.

In their latest update, the NGFS propose using a GDP damage estimate based on the Kotz et al paper ‘The economic commitment of climate change’, 12 which estimates that physical risks from climate change in a current policies scenario might reduce GDP growth roughly 1/3rd by 2100, i.e. GDP is still forecast to grow in this scenario, but to grow less than it would if climate change didn’t occur.13

Reference 12 is to this paper.

The authors have retracted this paper

Oh. And when we go look at the paper elsewhere we find that:

These 148 committed damages comprise a permanent income reduction of 17% on average globally (population weighted average) in comparison to a baseline without climate change impacts

They are measuring how much less growth we will get, not an absolute fall in GDP itself. On the sensible grounds that an actual fall is not something anyone at all takes seriously.

Oh, and, of course, that Kotz et al paper gains its truly bloodcurdling results only when using RCP 8.5 as the guideline. You know, the one that even the IPCC has now agreed ain’t gonna happen (and, of course, you read it here that it never was going to anyway).

So, the emeritus professor of geophysical and climate hazards assumes a fall in GDP, rather than a fall in the growth of GDP, from a retracted paper, based upon a retracted socioeconomic pathway, that paper detailing how it is a fall in the growth rate not a fall in the level of GDP that is to be worried about.

Climate change reporting, eh?

Tim Worstall