evidence: Forcings: The initial drivers of climate. [...] - Greenhouse gas emissions. Since the Industrial Revolution, concentrations of greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have risen in the atmosphere. Burning fossil fuels such as coal, oil, and gas has increased the concentration of atmospheric carbon dioxide (CO2) from 280 parts per million to 416 parts per million.2 These greenhouse gases absorb and then re-radiate heat in Earth’s atmosphere, which causes increased surface warming. [...] The most abundant greenhouse gas, it acts as a feedback to amplify climate warming forcings. Water vapor increases as Earth's atmosphere warms, making it an important feedback mechanism to the greenhouse effect.