“Human activities, especially burning fossil fuels and land-use change such as deforestation, are altering the global carbon cycle by increasing atmospheric carbon dioxide concentrations.”
The evidence firmly supports this statement. Multiple authoritative scientific assessments and direct atmospheric measurements show that burning fossil fuels and land-use change have raised atmospheric CO2 and altered the global carbon cycle. Natural sources of CO2 exist, but they do not explain the sustained modern increase, which is attributable to net human emissions.