Climate sensitivity and variability

The Earth's climate tends to be in an energy balance between absorbed incoming solar radiation and outgoing infrared radiation emitted from the Earth. Approximately 30 percent of the incoming solar energy is reflected by clouds, the surface and aerosol particles. The ratio of the reflected to the incoming solar radiation is known as the planetary albedo. In response to the solar heating, the Earth emits infrared radiation back to space in order to achieve energy balance:

The greenhouse effect is the difference between the infrared radiation emitted by the surface and what is emitted to space by the atmosphere. The strength of the greenhouse effect depends mainly on the presence of clouds and the composition of the atmosphere, for example water vapor and carbon dioxide. Climate sensitivity is then the magnitude of the climate system response to a perturbing influence, for example variations in the solar radiation and altered composition of the atmosphere due to vulcanic eruptions or human emissions. Climate variability is the temporal variations of the climate system around a mean state on longer timescales. The term natural climate variability is further used to identify climate variations that are not attributable to or influenced by any activity related to humans.