In comparison to a giant asteroid, yes. The effects of those are somewhat well established, and if we’re willing to suppose something even bigger from interstellar space, you could probably destroy most of the biosphere. But I hope you don’t think the description of life having time to adapt and relative comfort is a good way to put it without such a comparison.
The whole problem of global warming is that it happens on a timescale of centuries, which is faster than what ecosystems can keep up with. Sure, some things can find new niches, but then other things may not adapt well to them; an easy example is the crisis of pine beetles, which are destroying large sections of the boreal forest now that they don’t freeze.
Yes, over millions of years things will start finding a new equilibrium, but expecting only a few casualties along the way is entirely wishful thinking. kehvan is being sophistic to point out that prehistoric mass extinctions aren’t generally from warming, because we already have everything disrupted for other reasons, and warming this fast is unusual.
And this applies to people too. It’s long been noted that global warming is expected to cause all sorts of problems and wars for resources. Realistically this doesn’t mean civil war in Norway, but would start in places that are unstable; not creating but exacerbating existing conflicts. Reading up on Syria, it seems this has been an important contribution to its civil war.
Global warming is not a hipster way of saying pollution, but rather it is something like acid rain or ozone depletion, recognizing the peculiarly distant effects of one particular sort of pollution. Recall both acid rain and ozone depletion were only staved off because people took them seriously and took measures against the specific pollutants responsible. It’s not manipulative to hope people might do the same here.
