The heat is on Rising surface air temperatures are understood to cause glacial melting, but it is becoming increasingly clear that the ocean also has a strong impact. Cook et al. studied glaciers that drain the Antarctic Peninsula and found a strong correlation between mid-depth ocean temperatures and glacier-front changes along the peninsula's western coastline. Glaciers in the south, which are exposed to warmer waters, have undergone significant retreat, while those in the northwest, which terminate in cooler waters, have not retreated as much or as uniformly. Thus, ocean-induced melting appears to be the main cause of glacial retreat in the region. Science , this issue p. 283