The Earth’s climate has been constantly evolving at varying rates since the very beginning, yet these fluctuations have been slow in comparison to the current one. It is important to consider the speed of this variation, the so-called “timescale” of the changes, in order to understand the different contributions of natural and anthropogenic activities to current climatic changes.

The average temperature is regulated by the balance between incoming and outgoing energy, which determines the Earth’s energy balance. As such, any factor that causes a change to the amount of incoming or outgoing energy, which is sustained over a long period (decades or more) can lead to climate change. Some of these factors could be natural or “internal” to the climate system, such as changes in volcanic activity, solar output or the Earth’s orbit around the Sun.