Ozone occurs naturally in small amounts in the lower atmosphere and in high concentrations in the stratosphere, where it protects life from UV radiation. Depletion of the ozone layer allows more UV to reach the surface, risking damage to humans, animals, and plants. Greenhouse gases like carbon dioxide and chlorofluorocarbons trap heat in the atmosphere, causing the greenhouse effect and global warming as less heat escapes into space. The hydrological cycle and carbon cycle are impacted by climate change.