How do human activities affect climate?
* A: Human activities such as fossil fuel burning, industrial activities, land-use change, animal husbandry, and fertilized and irrigated agriculture lead to increases in greenhouse gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which contribute to the greenhouse effect and cause the surface temperature of the Earth to increase. Global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values (IPCC 2007).
