that's not true! climate change is not going to 'kill everyone'. it is going to kill many people, yes, and turn many more into refugees, and cause economic disasters that will cause widespread suffering. which is why it is so vital for socialists to do the work to mobilize and build systems and organizations capable of fighting back against the inevitable fascist response to increased poverty and waves of refugees. so, y'know, assuming that by 'maintain hope' you mean, like, 'work for the sake of a positive political project' and 'envision the future', it is because i do not think anyone can afford not to.