The sun’s rays hit the earth in the form of ultraviolet radiation. A part is reflected. On their way into the atmosphere, gases such as carbon dioxide (CO2), ozone and water vapour are reflected back to earth in the form of infrared radiation. This effect warms up the earth like a greenhouse and ensures a mean temperature of 15 °C (instead of -18 °C). This natural balance is disturbed by humans through high gas emissions, which reflect more and more radiation to the earth, causing the temperature to rise. This is the anthropogenic greenhouse effect that contributes to the current climate change.