Summer sea ice increased around the Eastern Settlement, with direct impacts on navigation, harbor seals, and quality of pasture along shores (48). The increasing sea ice would also have affected the coordination of communal labor during the vital summer months. The cumulative effects of reduced summer growing seasons (sometimes occurring in strings of successive summers) (43) and rising sea levels (42) would have both reduced grazing and fodder production and increased winter byring time and overall fodder need. Increased North Atlantic storminess (especially after A.D. 1425) would have increased hazards to sailing, threatening voyages to the Northern hunting grounds for walrus and the vital communications with Norway, the lifeline for both exports and imports.
A general reduction in summer temperatures would have had adverse impact on stock survival, while sharpening vertical zonation effects to the disadvantage of all upland farms, especially those farms in the more arctic Western Settlement. As Fig. 3 indicates, in the early 14th century, the overall cooling trend was associated with alternating extremes of warm and cold that far exceeded the range of the prior decadal-scale experience and therefore, fell outside the expected range of Norse TEK.
Collectively, these environmental changes would have degraded subsistence flexibility, decreased environmental predictability, and driven threshold crossing in the marine ecosystems related to the Eastern Settlement. The small Western Settlement (with a maximum likely population of 600–800) failed sometime in the late 14th century. Although the end of the Western Settlement is not completely understood, a likely proximate cause was isolation combined with late winter subsistence failure, plausibly connected to climate change (25, 43).
The much larger Eastern Settlement did not go extinct along with the Western Settlement, enduring until the mid-15th century.