Earth’s climate has been changing for billions of years, and it varies on seasonal, annual, decadal, and longer timescales. Due to these natural variations that occur, people who study the climate look at 30 years of weather data at a minimum- and typically much longer- when they want to see the climate pattern for a region.
Climate variability refers to variations in climate on time scales of seasons to decades and is generally controlled by natural ocean and atmospheric processes like the El Niño Southern Oscillation, Arctic Oscillation, and the North Atlantic Oscillation (References 1-3)
Climate variability explains how one winter can be cold and snowy, while the next is milder; or, how one decade is much drier than normal.
Climate change describes long-term (decades or longer) and persistent changes in the climate of a location and occurs because of natural and/or anthropogenic (human) processes. Climatology, the study of climate science, looks at a minimum of 30 years—or 3 decades—of weather pattern data to describe the climate, or change in climate, of a particular region.
Natural processes that can produce a change in Earth’s climate include variations in solar energy received by Earth arising from variable solar activity or slow orbital changes (Reference 4).
Anthropogenic, or human, processes that can produce a change in Earth’s climate include the burning of fossil fuels (which releases greenhouse gases) and land use changes like urbanization, deforestation, and desertification (Reference 5)