According to Hupfer and Kuttler (2005), the term "climate variability" describes a significant change in the statistical properties of one or more climate parameters. Climate variability occurs at all temporal and spatial scales beyond individual weather events (Glossary, IPCC 2019). 

Basically, a distinction can be made between internal and external climate variability..

Internal causes of climate variability are natural processes within the climate system. They are caused by fluctuations in the ocean-atmosphere interaction (ENSO phenomenon), fluctuations in the circulation of the atmosphere (NAO) or the oceanic current system (thermohaline circulation). (Source: Hamburger Bildungsserver)

In the case of external causes of climate fluctuations, natural driving factors must be distinguished from anthropogenic driving factors. Influences from solar radiation and solar activity, effects of volcanic eruptions or plate tectonic changes are among the natural causes.

Anthropogenic forcing factors on the climate system are, for example, the emission of greenhouse gases into the atmosphere or the change of the land surface in the context of land use changes. (Source: Hamburger Bildungsserver)

Climate Change
Climate change describes the change in the state of the climate, which can be described by statistically significant changes in one or more climate parameters that persist over a long period of time (at least 10 years according to IPCC). (Glossary, IPCC 2019)