Question

The rate of solar energy striking Earth averages 168 watts per square meter. The rate of energy radiated from Earth's surface averages 390 watts per square meter. Comparing these numbers, one might expect that the planet would cool quickly, yet it does not. Why not?

Short answer

In summary, the Earth does not cool down quickly despite radiating more energy than it receives from the sun because factors like the greenhouse effect, albedo, and the role of the atmosphere help maintain its energy balance. The greenhouse effect helps retain heat within the Earth's atmosphere, preventing the planet from cooling down too quickly. The Earth’s albedo, or reflectivity, affects its ability to absorb solar energy and maintain a balanced temperature. The Earth's atmosphere also plays a critical role, acting as a blanket to retain energy and warming the lower layers. These factors combine to maintain the Earth's temperature despite the difference in incoming and outgoing energy rates.

Step-by-step solution

Understand the Earth's energy balance

Earth's energy balance is mainly maintained by the absorption and reflection of solar radiation and the radiation of energy back into space. The amount of solar energy absorbed by Earth, mainly from shortwave radiation, is equal to the amount of energy radiated back to space in the form of longwave radiation. This balance is crucial for maintaining Earth's temperature.

Consider the greenhouse effect

The greenhouse effect plays an essential role in maintaining Earth's temperature. Greenhouse gases, such as water vapor, carbon dioxide, and methane, absorb part of the outgoing longwave radiation radiated by Earth's surface. These gases then reradiate the energy in all directions, with some energy going back to Earth's surface. The greenhouse effect helps retain heat within the Earth's atmosphere, preventing the planet from cooling down too quickly.

Reflect on albedo

Albedo is a measure of the Earth's reflectivity, which affects its ability to absorb solar energy. A higher albedo means more sunlight is reflected back into space, while a lower albedo means more sunlight is absorbed by the Earth. The Earth's albedo is determined by various factors, such as the presence of clouds, ice, snow, and vegetation. Earth's average albedo is around 30%, meaning 30% of incoming solar radiation is reflected back into space, and about 70% is absorbed by the Earth.

Discuss the atmosphere's role

The Earth's atmosphere plays a vital role in the energy balance. It absorbs and scatters incoming solar radiation and radiates energy back into space. The atmosphere also acts as a blanket, helping to retain some of the energy radiated by the Earth's surface within the atmospheric layers. This results in the warming of the Earth's lower atmosphere, known as the troposphere.

Conclusion

In summary, the Earth does not cool down quickly despite radiating more energy than it receives from the sun because of factors such as the greenhouse effect, albedo, and the role of the atmosphere. The Earth's energy balance and its interaction with the atmosphere maintain the Earth's temperature and keep it from cooling too quickly.