Energy from the sun enters the earth's atmosphere as short-wave radiation. This is absorbed by the earth's surface and is then radiated out into the atmosphere as long-wave radiation. Greenhouse gases have certain properties that mean that they absorb and re-emit this long-wave radiation. This process leads to global warming, which drives climate change.
Carbon dioxide (CO2) is the most important greenhouse gas being emitted by humans.
The atmosphere is composed of different gaseous constituents but the most important in terms of Climate change are the so-called 'greenhouse gases'.
Radiation from the sun is not absorbed particularly well by greenhouse gases, but it does warm the Earth's surface, the atmosphere and clouds which then emit energy back to space in the form of infrared (long-wave) radiation.
Greenhouse gases are quite efficient at absorbing and re-emitting radiation at specific wavelengths within the spectrum of infrared radiation and so act like a blanket that restricts loss of this radiation into space. As a result, the more that is trapped, the greater the warming.
The greenhouse effect is natural and without it the Earth would be considerably colder. The primary greenhouse gases are: Water vapour (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and ozone (O3).
The is an international attempt that contains legally binding commitments, in addition to those included in the UN Framework Convention on Climate Change, targeted at reducing anthropogenic greenhouse gas emissions.