evidence: Earth absorbs energy from sunlight, but as the surface warms, it also emits energy in the form of infrared radiation (which we know of as heat) out into space. Water vapor and CO2, however, act like a cap, making it more difficult for Earth to get rid of this energy. Without gases like these to absorb the energy, our planet’s average surface temperature would have been near zero degrees Fahrenheit. [...] Both water vapor and CO2 are responsible for global warming, and once we increase the CO2 in the atmosphere, the oceans warm up, which inevitably triggers an increase in water vapor. But while we have no way to control water vapor, we can control CO2. And because we are increasing the amount of CO2 in the atmosphere by continuing to burn fossil fuels, even in relatively small amounts compared to the entire mass of the atmosphere, we are disturbing the entire heat balance of the planet.