The IPCC is full of scientists and they have made that claim:
No, it's not.
They're not. Just ask Antarctica. As for the Arctic, that's been happening since the 1850s, but all the predictions of an ice free pole by 2007 (I mean, 2010...I mean, 2014...I mean, 2017...I mean, 2020...) have been, shockingly, wrong.
It never existed but...let's just say 1997 (when the 1970-2000-ish warming period ended).
Of course not. Don't be a racist.
Analysis of the sediment layer seems to indicate that there was, indeed, a cosmic impact.