Within the Earth system, vertical layering is critical to understanding the energy flows that define our climate. The surface is warmed by absorbing sunshine during daytime, yet receives much more downward radiation from the overlying warm air during both day and night. The surface cools mostly by emission of infrared radiation, and to a lesser extent by evaporation of surface water and through direct warming of surface air. The atmosphere is warmed from below by absorbing the upwelling infrared form the surface and also by condensing water as cloud droplets. A small amount of atmospheric warming is contributed by rising “thermals:” updrafts driven by buoyancy.
Tropical regions receive much more radiant energy from the Sun and atmosphere than they emit and the poles receive much less than they emit. Lateral motions of the air (wind) and oceans (currents) transport excess energy as heat from the tropics to the poles. These transports account for nearly all weather on Earth and maintain a habitable climate almost everywhere. The Earth’s surface climate is determined by a combination of all these vertical and lateral energy flows.