Human activities contribute to climate change by causing changes in
Earth’s atmosphere in the amounts of greenhouse gases, aerosols (small
particles), and cloudiness. The largest known contribution comes from the
burning of fossil fuels, which releases carbon dioxide gas to the atmosphere. Greenhouse
gases and aerosols affect climate by altering incoming solar radiation and
out-going infrared (thermal) radiation that are part of Earth’s energy balance.
Changing the atmospheric abundance or properties of these gases and particles
can lead to a warming or cooling of the climate system. Since the start of the
industrial era (about 1750), the overall effect of human activities on climate
has been a warming influence. The human impact on climate during this era
greatly exceeds that due to known changes in natural processes, such as solar
changes and volcanic eruptions.