The nuanced answer is IF climate change that is predicted by the UN, etc was real, THEN it would be the biggest threat to humanity.
That's a big if though. Remember 2 things:
1) The UN is an organization run by globalists who want a global agenda. This is not conspiracy, this is their stated mission
2) Creating fear is an excellent way to grab power
Beyond the tin foil hat wearing, there's this:
The climate has seen warming over the past 40 years, this is indisputable. However, the rate of change and the effects of that change seem to be overblown. Al Gore's Inconvenient Truth predicted a whole bunch of calamities that were supposed to be underway by now, but aren't. The polar ice caps seem to be stabilizing after years of decline. I could go on, but you get the idea.
It's a very nuanced issue. I'm not sure what's correct or what to do. What I do know is that I don't want power to continue to consolidate among the globalist elite class, which is precisely what they are trying to do with climate change hysteria.