Iceland, so named to discourage conquest by expanding empires, is not at all ice covered, like Greenland

Question:

Iceland, so named to discourage conquest by expanding empires, is not at all ice covered, like Greenland and parts of Siberia, even though it is not far from the Arctic Circle. The average winter temperature of Iceland is considerably higher than it is in regions at the same latitude in eastern Greenland and central Siberia. Why is this so?