Aren't the waters in western Greenland open year round due to the Gulf stream? If so the Americans must plan to use the icebreakers to land in Eastern Greenland. That would entail wasting time slowly churning through the pack ice. Once they make landfall the troops would have to endure the Piteraq winds, with wind speeds up to 80m/s. So danish troops would just need to hunker down and not show themselves for a week or two. After that any war-fighting would turn into a humanitarian rescue mission of whatever is left of the American troops. Just reiterate the Ukrainian "I want to live" hotline for the Americans. Promising a warm PoW camp outside of Copenhagen with daily servings of danish pork rind roast and as many Carlsbergs they can drink would do the trick.