Arctic ice pack
Sea ice is important for the heat balance of the polar oceans:  it insulates the (relatively) warm ocean from the much colder air above. With ice,  less heat is lost from the oceans. Sea ice is highly reflective of solar radiation, reflecting about 60% of incoming solar radiation when bare and about 80% when covered with snow. This is due to a feedback known as the albedo effect. This is much greater than the reflectivity of the sea (about 10%). The ice also affects the absorption of sunlight at the surface.