Earth’s natural climate system consists of several subsystems (spheres). The individual subsystems are closely connected by material and energy flows (e.g. the water cycle and carbon cycle) and respond to changes at varying speeds.
The climate system is highly complex and consists of five main components – the atmosphere, hydrosphere, cryosphere, geosphere and biosphere – as well as the interactions between them. The climate system changes over time due to the influence of its own internal dynamics and due to external factors like volcanic eruptions, fluctuations in solar radiation, and anthropogenic influences like changes in the composition of the atmosphere and land use.