Passage Summary: The author argues that cold weather couldn't have killed off the Norse, because the Inuit were living in the same cold and did just fine.

Conclusion: The author concludes that the temperature drop could not have been the reason the Norse settlements were wiped out.

Reasoning: The author points to the Inuit settlers, who lived in the same cold environment during the same period and survived long after the Norse were gone.

Analysis: The author uses a classic refutation technique: the counterexample. By showing that another group of humans (the Inuit) survived in the same conditions, the author undermines the claim that those conditions were 'too cold for human habitation.' I identified this by looking at how the author uses the Inuit's success to invalidate a causal explanation for the Norse's failure. The argument moves from a specific observation of survival to the rejection of a general claim about habitability.