To me, it's our inability to solve climate change that makes me so pessimistic. Not because of the climate itself, but because of the ability of a smallish set of people completely insulated from reality to thoroughly prevent our ability to do anything about it.
Climate change is a relatively straightforward problem with a somewhat-less-straightforward set of solutions. Whatever solution we choose, it will involve a group effort. Few people want to take on the costs of it while everyone else benefits. And it just so happens that one set of people, among the very largest polluters, deny that it's even happening -- in a variety of mutually contradictory ways. Their failure is obvious and overwhelming, and they are a minority of the world, but it's sufficient to derail progress worldwide.
That's why I'm pessimistic. I used to believe that anybody that far out of touch with reality must surely be booted out of power sooner or later. I've been proven wrong: they gain more power by the day. And that one belief comes with a constellation of similar false beliefs, mutually reinforced, and each participant goading the other to proclaim the falsehoods more loudly.
I'm sorry that means I'm contributing to the problem you're citing, but I've only seen it get worse in my lifetime. The upward progress of the world had so much momentum that it took a long time to turn around, but the exponential increase in insanity means I just can't see any way that it doesn't do so.
I try, nonetheless, to behave as if I were optimistic. I do make my own small contributions to progress. But I expect to see them all wiped away or made irrelevant.