Climate
and Earth’s Energy Budget
by
Rebecca Lindsey
The
Earth’s climate is a solar powered system. Globally, over the course of the
year, the Earth system—land surfaces, oceans, and atmosphere—absorbs an average
of about 240 watts of solar power per square meter (one watt is one joule of
energy every second). The absorbed sunlight drives photosynthesis, fuels
evaporation, melts snow and ice, and warms the Earth system.
The
setting sun, photographed from the International Space Station.
Solar
power drives Earth’s climate. Energy from the Sun heats the surface, warms the
atmosphere, and powers the ocean currents. (Astronaut photograph
ISS015-E-10469, courtesy NASA/JSC Gateway to Astronaut Photography of Earth.)
The
Sun doesn’t heat the Earth evenly. Because the Earth is a sphere, the Sun heats
equatorial regions more than polar regions. The atmosphere and ocean work
non-stop to even out solar heating imbalances through evaporation of surface
water, convection, rainfall, winds, and ocean circulation. This coupled
atmosphere and ocean circulation is known as Earth’s heat engine.
The
climate’s heat engine must not only redistribute solar heat from the equator
toward the poles, but also from the Earth’s surface and lower atmosphere back
to space. Otherwise, Earth would endlessly heat up. Earth’s temperature doesn’t
infinitely rise because the surface and the atmosphere are simultaneously
radiating heat to space. This net flow of energy into and out of the Earth
system is Earth’s energy budget.
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