Air in direct contact with the sun-warmed ground becomes warm and buoyant. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth system.Īn additional 5 percent of incoming solar energy leaves the surface through convection. About 23 percent of incoming solar energy is absorbed in the atmosphere by water vapor, dust, and ozone, and 48 percent passes through the atmosphere and is absorbed by the surface. This energy plays no role in Earth’s climate system. This state of balance is called radiative equilibrium.Ībout 29 percent of the solar energy that arrives at the top of the atmosphere is reflected back to space by clouds, atmospheric particles, or bright ground surfaces like sea ice and snow. In other words, the energy budget at the top of the atmosphere must balance. For Earth’s temperature to be stable over long periods of time, incoming energy and outgoing energy have to be equal. This flow of incoming and outgoing energy is Earth’s energy budget. The numbers in this article rely most heavily on direct satellite observations of reflected sunlight and thermal infrared energy radiated by the atmosphere and the surface.Įarth’s heat engine does more than simply move heat from one part of the surface to another it also moves heat from the Earth’s surface and lower atmosphere back to space. Estimates come from satellite observations, ground-based observations, and numerical weather models. Different estimates exist, and all estimates have some uncertainty. Note: Determining exact values for energy flows in the Earth system is an area of ongoing climate research. Only half the Earth is ever lit by the Sun at one time, which halves the total solar irradiance. The total solar irradiance is the maximum possible power that the Sun can deliver to a planet at Earth’s average distance from the Sun basic geometry limits the actual solar energy intercepted by Earth. If for just one hour, you could capture and re-use all the solar energy arriving over a single square meter at the top of the atmosphere directly facing the Sun-an area no wider than an adult’s outstretched arm span-you would have enough to run a refrigerator all day. How much power is 1,360 watts? An incandescent light bulb uses anywhere from 40 to 100 watts. (Before scientists discovered that it varies by a small amount during the sunspot cycle, total solar irradiance was sometimes called “the solar constant.”)Ī watt is measurement of power, or the amount of energy that something generates or uses over time. This amount of power is known as the total solar irradiance. At Earth’s average distance from the Sun (about 150 million kilometers), the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter, according to measurements made by the most recent NASA satellite missions. At that temperature, most of the energy the Sun radiates is visible and near-infrared light. The surface of the Sun has a temperature of about 5,800 Kelvin (about 5,500 degrees Celsius, or about 10,000 degrees Fahrenheit).
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