1. Solar Energy
Chapter 22.2

2. Radiation
All of the energy that Earth receives from the sun travels through space between Earth and the sun as radiation.
Radiation travels in the form of waves at approximately 300,000 km/s.
The waves that make up all forms of radiation are called electromagnetic waves.

3. The Atmosphere and Solar Radiation
About 70% of the solar energy that reaches Earth is absorbed by Earth’s land and ocean surfaces and by the atmosphere.
The remainder is reflected back into space
Most incoming infrared radiation is absorbed by carbon dioxide, water vapor, and other molecules in the troposphere.
The absorption of energy from the ground heats the lower atmosphere and keeps Earth’s surface warmer than if there was no atmosphere.

4. The Greenhouse Effect
The warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate radiation
Earth’s atmosphere slows the escape of energy that radiates from Earth’s surface.

5. Human Impact on the Greenhouse Effect
The amount of solar energy that enters Earth’s atmosphere is about equal to the amount that escapes into space.
Human activities may change this balance causing the average temperatures to increase.
Increases in the amount of carbon dioxide may intensify the greenhouse effect and may cause Earth to become warmer in some areas and cooler in others.
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6. Variation in Temperatures
Radiation from the sun does not heat Earth equally at all places at all times.
The temperature of the atmosphere in any region on Earth’s surface depends on several factors, including latitude, surface features, and the time of year and day.

7. Latitude and Seasons
Latitude is the main factor affecting the amount of solar energy that reaches any point on Earth’s surface.
Because Earth is a sphere, the sun’s rays do not strike all areas at the same angle.
The energy that reaches the equator is more intense than the energy that strikes the poles, the average temperatures are higher near the equator than near the poles.

8. Water in the Air and on the Surface
Because water vapor stores heat, the amount of water in the air affects the temperature of a region.
Land areas close to large bodies of water generally have more moderate temperatures
The wind patterns in an area also affect temperature.
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9. Conduction and Convection
The transfer of energy as heat from one substance to another by direct contact is called conduction.
Example: the heating of a metal spoon in boiling water
The process by which air, or other matter, rises or sinks because of differences in temperature.
Convection occurs when gases or liquids are heated unevenly.
Example: how water heats to a boil, mantle in the Earth

10. Reading Check
Why are deserts generally colder at night than other areas are? Deserts are colder at night than other areas are because the air in deserts contains little water vapor that can absorb heat during the day and release heat slowly at night.