Nuclear war was and is a bigger threat. Climate change has been a threat for decades, before quitting became a pastime of the Americans and the West.
Wars and other localized dangers are much greater threats for people involved; WWII was a much greater threat to the West. Black people in the US have faced greater threats for most of American history.
I’d argue climate change was never so serious. It’s getting worse and worse and is happening right now. It’s possible we’re passing a tipping point and that it will accelerate while feeding on itself.
Nuclear war is a hypothetical in comparison (although it would also be pretty bad but it’s not currently happening).
Black people in the US aren’t the only persecuted population in the world, and it’s targeted (by definition); It’s not universal.
Climate change or nuclear war would wipe out humans as a species (and most other living things) indiscriminately, regardless of race.