Every Wonder why?

Because once upon a time when Norwegian/Icelandic settlers came to Greenland, the general temperature was quite high so Greenland was actually green. And if you want people to move there, you call it Greenland. Not "white-with-a-dash-of-green"land. Iceland however isn't really green. Not icy either, it's black and grey with dashes of green and red and blue :-)

grennland is cold because it is way too above iceland.

Greenland was likely called that in order to encourage settlement or to instill pride in it's owners.