Where the island is located is as important as the fact that it's an island. Ireland, for example, is located at the same latitude as lower Siberia or Middle Canada, both places that are a little cold in winter. However, it sits smack in the middle of the Gulf Stream, a very warm current that flows from the Gulf of Mexico. If it didn't have such a current, it would be a lot colder. The lower Kamchatka peninsula is about the same latitude, but it doesn't have a nice warm current. That place gets very cold and unpleasant, I understand.