Re: The "We're all going to die" hand-waving aside
"I think this is the thing that jars - there's no 'going' involved; a species that becomes extinct hasn't gone anywhere, at least not anywhere it is possible to come back from."
But your very statement gives the justification: they're going away...forever.
"This might lead to a reduction in human population, probably in a rather unpleasant way for large numbers of us, but I don't think it's likely to do us in as a species, nor impact life in general on the planet in the long term."
You should look up "thermogeddon". There's a very real concern that certain parts of the world, if allowed to warm significantly, will become literally uninhabitable: not because it's underwater but because it'll become too warm for our bodies to cope without outside assistance. Thing is, if things get warmer, habitable land will start becoming compressed into fewer countries which can have a significant political effect.