Support for the Paris Accord is typically thought to be one of those “prudential judgments” for Catholics. So the possibility that the US will pull out may seem to be a matter of reasonable disagreement among “people of good will.” I want to suggest two reason to think that is very unlikely, and that in fact support for the Paris Accord – or at least for some binding global agreement on carbon emissions – is not a matter of prudential judgment, but an essential principle of Catholic practice.
The two reasons are these. One is the fact of the greenhouse effect. The specific timetable of climate change and its precise effects are debated – not much, but they are. The greenhouse effect is not. It is a much a matter of clarity as is how children are conceived. As such, it is contrary to both faith and reason to deny it.
The other is that collective action is the only viable way to manage a resource like the atmosphere, because of what it is. When Pope Benedict teaches in Caritas in Veritate that “the rich nations can and must reduce their energy use,” he clearly requires us to cooperate on this matter. The Paris Accord – perhaps too weak, but nevertheless of great significance – is that cooperation happening. There is no doubt that Pope Francis’s intention, completely consistent with the authoritative teaching of Pope Benedict, in issuing the encyclical Laudato Si in 2015 was to help push toward agreement at Paris. And it’s encyclical-level teaching – the strongest we have short of a Council.
Therefore, it’s wrong to pull out unless there is a viable collective action alternative. There is not, and none (to my knowledge) is being proposed. Therefore, it’s wrong.
There a LITTLE prudence in the above reasoning. But not much. It’s just pretty much the reasoning you’d have to follow as a Catholic if you were interested in listening seriously to the Church’s Magisterium.