This is excellent advice for matters of opinion or belief or judgement, even ideology or politics.
Rick Fischer

Please link to the source that claims that the temperatures on Greenland are -10°C. I’m puzzled by that number considering the size of Greenland and the fact that even Greenland has seasons. What exactly makes this number a “fact”?

According to the official Greenland website, cities like Upernavik and Narsarsuaq absolutely do have temperatures above 0°; up to +10°C in the summer, actually. Those are the lower regions of Greenland of course, and the ice sheet is higher above sea level where it is colder. But if you look at satellite images that claim to depict the melting of the ice sheet, the melting is happening exclusively at the edges of it — so in regions that aren’t quite as high above sea level. If temperatures are indeed rising, then it is only logical that ice will melt first in the lower regions where temperatures weren’t super-cold to begin with.