Meltponds form on polar sea ice when temperatures rise during summer months. They are more common in the Arctic, where they often originate at the site of seal-breathing holes, than in the Antarctic. Some (bottomless) ponds appear almost black; others take on a striking turquoise hue from the sea ice beneath them. Because meltponds are darker than the surrounding ice, they absorb rather than reﬂect the twenty-four-hour Arctic summer light and warmth. The balance between this absorption and reﬂection of the sun’s energy is a signiﬁcant climate factor in the Arctic. Scientists know that the Arctic sea-ice cover has decreased signiﬁcantly in the last thirty years, and are monitoring the ratio of meltponds to ice during summer months to determine the extent to which the ponds accelerate sea-ice melting.