I've heard that Greenland was truly green and that the ice around the
West Coast of Greenland was only seasonal so that it might have been
feasible for a ship to circum-navigate Greenland in the late 1300s and
early 1400s.  This is attributed to signficantly higher tempartures in
Greenland than exist in the last 500 years.  Is this true?

What do we know about Greenland prevaling temparatures in the late
1300s and early 1400s compared to today?

"Viking colonies in Greenland abruptly vanished toward the end of the
14th century. Why? One clue comes from ice cores... In colder periods,
seas become stormier because of the greater contrast in temperatures
between the tropics and the poles, and so more sodium--an indicator of
seasalt--winds up on the ice caps. About 1400 AD, the cores at both
poles clearly show a sharp rise in sodium, which some scientists say
marks the onset of the Little Ice Age, a period of much cooler
temperatures that lasted into the 19th century. For the Vikings, a
series of abnormally cold winters in the late 1300s spelled doom."

http://www.pbs.org/wgbh/warming/stories/

You'll find lots of data here:

http://www.gisp2.sr.unh.edu/

To add to pinkfreud's excellent links, (pink's links?), also be aware
of what is often called the Medieval Warming Period -- here's a
discussion of MWP and the Viking travels:

http://www.wooster.edu/geology/tr/kbrady.html


Bottom line is that not a great deal really is know about the climate
in Greenland, since there is so little direct historical record. 
Everything we think we know is inferred from tree rings, dissolved gas
analysis, acidity flucuations, and so on.

But there does certainly seem to have been a warm spell in Greenland
for a few hundred years, prior to the little ice age freezing things
over again.


pafalafa-ga

You might be interested in the chart on page 3 of this document,
"Variation in MAGNITUDE of Greenland temperature, last 5,000 years":

http://members.iinet.net.au/~glrmc/Melb%20Rotary%20Figs%201-4.pdf