Climate change refers to long term shifts in Earth’s climate driven largely by human activities. The strongest evidence comes from multiple independent datasets. Direct air measurements since the late 1950s show carbon dioxide rising from about 315 ppm to over 420 ppm today. Ice cores extend this record back hundreds of thousands of years and reveal current levels are unprecedented in that span. Other greenhouse gases such as methane and nitrous oxide have also increased sharply.

Physics established in the 19th century explains that greenhouse gases absorb and reradiate infrared radiation, trapping heat. Satellite observations confirm reduced energy escaping to space at the wavelengths absorbed by these gases, while surface measurements show increased downwelling longwave radiation. Global average surface temperature has risen about 1.2 degrees Celsius since the late 19th century, with land warming faster than oceans and the Arctic warming especially quickly.

Observed changes align with expectations from increased greenhouse gases. Glaciers and ice sheets are losing mass, Arctic sea ice extent and thickness are declining, and global sea level has risen more than 20 centimeters since 1900, now increasing at an accelerating rate. Heat waves, heavy rainfall events, and some types of drought have become more frequent or intense in many regions.

Climate models that include only natural factors such as solar changes and volcanic eruptions cannot reproduce the observed warming. When human emissions are included, the models match the pattern and magnitude of change. Current research therefore concludes that recent climate change is real, rapid, and primarily caused by human greenhouse gas emissions.