The departure of these Viking settlers coincided with the beginning of the period known as the Little Ice Age, which had a particular impact on the North Atlantic. But while cooling and freezing might seem likely to lower sea levels, a variety of factors combined to have the opposite effect in Greenland. So, the scientific consensus is basically, "It's whatever."
Colder? That's Global Warming and rising seas.
Warmer? That's Global Warming and rising seas.
Remarkably steady? That's Global Warming and rising seas.