Greenland was a farming community for the Vikings. It wasn't just the colder weather that did them in. It was totally deforesting the island. That's why the Vikings found their way to North America way back, in medeival times. They were looking for more wood and resources. (according to the book)
The deforestation eventually ended Greenland settlements along with natural climate change (cooling) in the 1400’s and 1500’s which made farming and cattle raising impossible.
The Vikings originally settled Greenland about 980. Approximately 20 years later they discovered North America. They failed to establish a permanent settlement in what they called Vinland (now Newfoundland) but there is evidence they visited North American periodically up to the late 1300s, possibly harvesting timber and fish.
Apparently the Scandinavians of the 1000-1400 era either did not have the population pressure to seek expanded colonies in North America, and the natural resources their explorations identified in North American were not valuable enough to economically transport back to the home country. By the 1300’s there was no interest in sustaining the outposts in either Greenland or North American in Norway and Denmark.