The Blanket of Air

Earth stays warm enough for life partly because of gases in its atmosphere. Energy arrives from the Sun mostly as visible light and warms the surface. The surface sends energy upward as infrared radiation. Greenhouse gases, including carbon dioxide, methane, and water vapor, absorb and re-radiate some infrared energy, slowing its escape to space. Without this natural greenhouse effect, Earth would be much colder.

Human activities have strengthened the effect. Burning fossil fuels raises atmospheric carbon dioxide, while other activities add methane and nitrous oxide. More heat-trapping gas changes the planet’s energy balance. Oceans absorb most of the excess heat, and land, air, ice, and living systems respond at different speeds.

“Stopping emissions” needs a precise meaning. Cutting annual carbon dioxide emissions slows the rate at which more carbon accumulates, but temperatures do not stabilize while net emissions remain above zero. At sustained global net-zero carbon dioxide (when human removals balance remaining human emissions), carbon-dioxide-caused warming is expected to approximately stabilize, not climb forever. The result also depends on other greenhouse gases and aerosols.

Stabilized temperature does not mean a return to the former climate. Carbon dioxide and stored ocean heat persist, ice sheets respond slowly, and sea level can keep changing for centuries. Reaching net zero therefore prevents additional carbon-dioxide-driven warming while leaving a long task of adaptation. The important lag is not a reason to think action has no prompt effect; it is a reason to distinguish halting further warming from reversing changes already made.