Ultraviolet
Although the air of the Earth is transparent to a broad range of ultraviolet, some ultraviolet sunlight is absorbed at a very high altitude by the ozone layer. Recent and ongoing destruction of ozone in high altitudes caused by human influence—mostly by industrial chemicals and air travel—has greatly increased the amount of ultraviolet light reaching the Earth's surface. This, in turn, has increased the risk of skin cancer to mankind, and this risk will only increase with time unless the ozone layer is better protected.