I need to figure out how much of the Sun’s energy is absorbed and reflected by the Earth
The radius of the Earth is about 4000 miles. So, the Earth has a cross-sectional area of πr² = 5 x 10^7 square miles.
The area of the sphere surrounding the Sun with radius 93 million miles (the distance from Earth to Sun) is about 3 x 10^16.
So, the Earth intercepts about 5 x 10^7 / 3 x 10^16 = .0000002 % of the Sun’s output of about 4 x 10^20 megaWatts, or about 7 x 10^11 megaWatts.
Since the Earth is in roughly thermal equilibrium with the Sun, we reflect the same amount that we absorb.
Of the sun’s energy that reaches Earth’s atmosphere, 30
percent is reflected back into outer space, 47 percent is
absorbed by Earth’s surface and converted into heat energy,
23 percent drives the hydrological (water) cycle, less
than one percent creates winds and ocean currents, and
only 0.03 percent is captured by plants and used in photosynthesis.
The 0.03 percent of the sun’s energy captured
by plants provides all the world’s food energy and produced
the stored fossil fuel energy (coal, oil, natural gas).
Thus, the sun is the primary source of all energy on Earth.
less than one billionth of the suns total energy even reaches earths outer atmosphere
of this less than one billionth
30% of it is immediately reflected back
47% absorbed by the atmosphere
23% runs the water cycle
.02%captured by photosynthesis
less than 1% drives the winds and ocean currents
AND ALL solar energy is ultimately re-radiated to space as HEAT!
The quantity you’re looking for is called the albedo. It’s been measured very accurately, and it varies from place to place over the surface of the earth…oceans, forests, deserts, etc. all have different characteristics.
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