Leave aside whether we believe these numbers or not.

The US has inflicted more than $1.9tn in damage to other countries from the effects of its greenhouse gas emissions, according to a new analysis that has provided the first measurement of nations’ liability in stoking the climate crisis.

The huge volume of planet-heating gases pumped out by the US, the largest historical emitter, has caused such harm to other, mostly poor, countries through heatwaves, crop failures and other consequences that the US is responsible for $1.91tn in lost global income since 1990, the study found.

Firstly, we need to know whether that is in fact a large number or not. The study covers 1990 to 2014. A reasonable estimate (not accurate by any means) is that the US economy is a $20 trillion a year one. The global economy over that period a $75 trillion a year one. Over 24 years that’s $500 trillion (rough numbers!) or $1,800 trillion. The damages are thus 0.4% of the US economy over the time period, or 0.1% of the global one.

It’s possible to start the argument back by noting that these are not really material numbers.

We then want to know what is the cost of stopping this near immaterial damage and that’s a big enough shouting match that we’ll leave that one aside for today.

But the really big thing is that it should always be a cost and benefit analysis. Has the existence of the US in the global economy been worth 0.1% of that economy over that quarter century? Have, for example, the flood of inventions - most of the internet and much of computing stems from there after all - added 0.1% to global economic production?

We’d say, on the face of it, obviously and clearly. But that’s not quite the point we wish to make here. There are costs and benefits to everything. Therefore we need to measure, before any decision making, both in order to be able to decide. For it’s the nett effect that matters, no?