The first basically holds that we should play up the problem, to increase urgency and a sense of crisis.
(I guess you could split these into two types of "optimism", but for simplicity I'll keep them together for now.)
If they see a problem as inevitable, or just a fact of life, they may opt for serenity, or even denial. Who spends all their effort for a hopeless cause?
But this is a mirage. Most social problems are so complex that we don't really know how solvable they are.
In practice, both optimists and pessimists consider themselves "realists".
On the climate issue, I prefer the optimistic, can-do attitude of @ramez to the more apocalyptic pronouncements of some other friends of mine.
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