Definition
Climate change refers to long-term shifts in temperatures, rainfall, wind patterns, and other features of the Earth's climate system. While the climate has changed throughout the planet's history, the term is now used mainly for the rapid changes of the modern era.
Scientific evidence shows that this modern warming is driven principally by human activity — chiefly the burning of fossil fuels, which releases greenhouse gases that trap heat in the atmosphere. It is one of the defining challenges of the twenty-first century.
Why it matters
How it works
Greenhouse gases such as carbon dioxide and methane let sunlight reach the Earth's surface but trap some of the heat that the surface radiates back. As human activity adds more of these gases to the atmosphere, the planet retains more heat, and average temperatures rise.
That warming ripples through the whole climate system. It melts ice, raises sea levels, alters rainfall, and shifts the patterns that ecosystems and farming depend on. Because the gases linger for a long time, today's emissions shape the climate for generations.