Albedo is the amount of solar energy reflected back into space by a planet or other body. The more solar energy an object reflects, the higher albedo it has. So the surface of the ocean or a large lake, which absorb a great deal or solar energy, have a higher albedo than, say, large expanses of desert sands, which reflect solar energy back into space. This has several implications for human life. One is that cities, with large amounts of paved blacktops, absorb a great deal of solar energy during the summer, making them significantly hotter than rural areas. Another, one which has received a great deal of publicity in recent years, is that the relatively high albedo of water can contribute to melting polar ice, which can threaten coastal areas. Perhaps most important on a large scale, the "greenhouse effect" lowers the overall albedo of the earth, causing the planet to absorb more energy, contributing to climate change.