Climate change is in part a natural phenomenon, influenced by solar energy, volcanic eruptions, changes in the Earth’s orbit, and oceanographic changes, among other things.
Humans are also responsible for climate change through activities like the combustion of fossil fuels, agriculture, and forestry, which emit GHGs. A greater concentration of GHGs in the atmosphere, by allowing sunlight to penetrate but absorbing a certain portion of the infrared radiation that bounces back from the Earth, contributes to an increase in the temperature at the Earth’s surface. The accumulation of GHGs and the corresponding temperature increase are then associated with climate changes like heavier precipitation in certain places.
According to the IPCC, human influence on the climate since 1750 is clear and has contributed to its warming.(10) NASA estimates that the average temperature at the Earth’s surface has risen by 0.8°C since 1889, and that the impact of humans on the climate has surpassed natural changes to the climate. These last have made the temperature vary by an interval of -0.2°C to 0.2°C, according to NASA. Human activity, for its part, has contributed to an increase of 0.8°C.(11)
10. Richard B. Alley et al., “Summary for Policymakers,” in S. Solomon et al. (eds.), Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, IPCC, 2007, p. 3.
11. NASA Earth observatory, Is Current Warming Natural?