Earth Radiation Budget
The Earth receives an average solar power of 342 W/m2. Its surface and clouds reflect about 30% of the light received. This phenomenon is called the albedo effect. The remaining 70% is absorbed by the atmosphere and the Earth’s surface, causing their temperature to rise. This heat is dissipated as infrared (IR) radiation directed towards the ground and the atmosphere. Some of this radiation is trapped by certain gases called greenhouse gases (GHGs). This phenomenon contributes to the temperature rise of the Earth’s atmosphere. Without these gases, the average temperature on Earth would be -18°C, and life as we know it would be impossible.
These gases are mainly water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3). However, since the beginning of the industrial revolution, the greenhouse effect has been amplified by the release of large quantities of GHGs into the atmosphere.
In the end, all the energy absorbed by the Earth and the atmosphere will be re-emitted back to space in the form of IR radiation, resulting in a balanced energy budget and a theoretically stable average temperature. However, this equilibrium temperature is higher in the case of an excess of GHGs. This is the cause of global warming.