The Milankovic theory relates global climate variations, especially cycles of glacial periods, to recurring orbital changes that affect the radiation intensity. The changing parameters are precession (direction in space of the earth's axis of rotation), tilt (the earth’s rotation axis to the plane of its orbit around the sun), and eccentricity (extent to which the earth's orbit around the sun differs from a circle). There is no explicit evidence for the accuracy of this theory. It is not doubted that the parameters have an effect, yet the Milankovic theory neglects interdependencies with other factors. The theory is often referred to by so-called climate sceptics.

In the context of climate protection, prevention of further climate change (especially through emission reductions).

In the context of the EU emission trading scheme, the EU member states establish a national allocation plan for each trading period which defines the number of allowances that they plan to distribute to individual plants in that trading period (so-called "cap"), and the criteria underlying the allocation.

Unit used to denote the concentration of an element in the air. One ppm denotes one particle of a given substance for every 999,999 other particles.