There's a difference between what caused former mass extinctions & what's causing one now!
There is also a thinning layer of the top cold water layers that lie beneath polar ice. If or when these layer thins to far then the warmer bottom layers of water will slowly melt more ice (there's a cycle starting here) which will also cause changes in the gulf stream. Why can't we agree it's just to risky to leave it all up to chance, because that's the best we're doing since we're not listening to science. By the time more studies conclude no more than the past studies (the out come depends on who's doing the study & who's paying for it) will all be in the grave.
Barry