Because a "change" like this would influence (and probably end) millions upon millions of lives.

I live maybe 45 minutes away from the Atlantic Ocean by car. A mega-tsunami or other catastrophic flooding event, whether manmade or otherwise, would probably kill me, my friends, my family and everyone I know if we couldn't evacuate in time. It's perfectly reasonable to be afraid of something like that.

Expand your worldview. People generally don't like it when other people die or when the status quo gets interrupted.

Because the earth should be getting colder at this point. We broke the natural evolution/change, which puts life as we know it in danger

Nobody is afraid of the earth. People are afraid of what we are unnaturally doing to it. And the potential wars, famine, and nation state collapses that it will drive in our lifetimes.

No big deal, really. /s