Eh? If global warming was not real, and there wouldn't be any negative sides from CO2 emissions, then it would of course be bad to reduce Co2 emissions by lowering the standard of living (assuming that you're an utilitarian and not a psychopath).

On the other hand, maybe you're talking about other negative environmental effects that are linked to activies that cause CO2 emissions.

I think well being of people should be maximized, and in the optimal situation there shouldn't be any lifestyle changes or "austerity" measures to reduce CO2 emissions if there's no reason to reduce CO2 emissions. If they're required, then of course it's reasonable to adopt them.