These are spectra, and neither extreme is "correct" and rooted in objective reality. Pessimism/optimism can be decoupled from other axes like ignorance/knowledge, acceptance/denial, awareness/delusion, etc. Assuming "climate change is happening" as fact, someone might exhibit climate change denial for any number of reasons. These are just illustrative sketches, not an effort to build some taxonomy of beliefs:
Ignorance: someone may be unable to comprehend the complicated climate system concepts, statistical concepts, nor noisy data.
Cynical pessimism: someone may believe it is happening and unavoidable, but they want to minimize their own inconvenience or discomfort prior to the end game.
Blind optimism: someone may just harbor a profound faith that things will work out in the end; to them, the people trying to address climate change seem like toxic pessimists who harbor delusions of grandeur!
That's a really interesting way to slice and dice it. When I read your first few sentences that's not how I interpreted it at all.
I got fact, fact, optimist. Optimist, fact. Fact, optimist, optimist.
But I'm not convinced that's a better way to go about it. What is likely needed is each of those chunks to be taken into context and when I look it at that, it's really "here is a problem and a solution to move things forward." To me that's optimistic. If it were pessimistic, I'd expect it to be "here is a problem and there's nothing we can do about it."