Climate change refers to long-term changes in the average weather patterns that have come to define Earths local, regional, and global climates. These changes have a broad range of observed effects that are evident in the environment, such as rising sea levels, melting glaciers, and more frequent and severe weather events like hurricanes, heatwaves, wildfires, droughts, and floods. Climate change is generally defined as a significant variation of average weather conditions over several decades or more.

Climate data records provide evidence of climate change key indicators, such as global land and ocean temperature increases, rising sea levels, ice loss at Earths poles and in mountain glaciers, frequency and severity changes in extreme weather, and precipitation. Since the pre-industrial period, human activities are estimated to have increased Earths global average temperature by about 1 degree Celsius (1.8 degrees Fahrenheit), a number that is currently increasing by more than 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade. The current warming trend is unequivocally the result of human activity since the 1950s and is proceeding at an unprecedented rate over millennia.

Climate change is measured over time by monitoring present-day weather and climate using earth-orbiting satellites, remote meteorological stations, and ocean buoys. Paleoclimatology data from natural sources like ice cores, tree rings, corals, and ocean and lake sediments have enabled scientists to extend the earths climatic records back millions of years. These records provide a comprehensive look at the long-term changes in the earths atmosphere, oceans, land surfaces, and cryosphere (frozen water systems) .

In summary, climate change is a long-term shift in global or regional climate patterns that is caused by human activities and has a broad range of observed effects on the environment.