What pledges must be made by the parties meeting at COP26 in Glasgow if there is to be a good chance of keeping the increase in temperatures above pre-industrial levels to less than 1.5°C, as the Intergovernmental Panel on Climate Change recommends? The answer, as I argued last week, is that they must be much more ambitious: above all, they need to cut emissions far faster.

It is not enough to offer St Augustine’s vow of “chastity, but not yet”. Pledges of “net zero” thirty years from now are too easy. It is necessary to cut emissions by close to 40 per cent by 2030, instead. The curve of emissions must be bent downwards now. That is economically and technologically feasible, albeit hard. Ten years hence, it will be too late to avoid irreversible damage without resort tothe risky geoengineering recently discussed by Gernot Wagner.

Between 2017 and 2021, the proportion of global emissions covered by some form of “net zero” target jumped more than 65 percentage points, to more than 70 per cent. Yet the “nationally determined contributions” (NDCs) agreed at COP21 in Paris, in 2015, are far from tight enough to achieve the needed reductions in emissions, especially by 2030. In that year, pledged emissions will exceed the upper limit imposed by the recommended 1.5°C ceiling by 20-23 gigatonnes of CO2 equivalent. (See charts.)