By that logic, it doesn’t make sense to fit a building with a sprinkler system when it’s only used for one hour out of a century.

The question should be whether AC would be used much, but whether it has a net benefit. And yes, the environmental impact should be taken into account.

To me, that depends (a.o.) on whether those 1,500 excess deaths get ‘compensated’ by lower death rates just after the heat wave (which would mean many of those who died lost ‘only’ a few weeks)