Problem 74 - Chemistry: The Central Science

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?

Step-by-Step Solution

Answer

The Earth does not cool down quickly even though the rate of energy radiated (390 watts per square meter) is higher than the rate of solar energy received (168 watts per square meter) due to the greenhouse effect. Greenhouse gases, such as carbon dioxide, methane, and water vapor, in the atmosphere trap and re-radiate some of the lost energy back to Earth, preventing Earth from losing too much heat to space and maintaining a stable temperature. This natural balance is essential for life on Earth and prevents rapid temperature fluctuations.

Step 1: Understand the energy input and output

To solve this problem, we must understand how Earth receives and loses energy. The primary source of energy on Earth comes from the Sun, which is 168 watts per square meter. Earth also loses energy on average 390 watts per square meter through the process of radiation. Let's compare these two values to understand why Earth does not cool down quickly.

Step 2: Investigate the greenhouse effect

The greenhouse effect plays a vital role in maintaining the Earth's temperature. This effect occurs when certain gases in Earth's atmosphere, such as carbon dioxide, methane, and water vapor, trap heat by absorbing the infrared radiation emitted by Earth's surface and re-radiating it back towards the surface. In this way, these greenhouse gases act like a thermal blanket, preventing the Earth from losing too much heat to space and maintaining a more stable temperature.

Step 3: Compare the energy balance between input and output

Since the amount of energy received by Earth (168 watts per square meter) is less than the amount radiated from its surface (390 watts per square meter), one might expect Earth to quickly cool down. However, the greenhouse effect maintains a balance between the energy input and output. The greenhouse gases in the atmosphere re-radiate some of the lost energy back to the Earth, reducing the net energy loss.

Step 4: Conclusion

The Earth does not cool down quickly even though the rate of energy radiated is higher than the rate of solar energy received because the greenhouse effect helps maintain Earth's heat balance. Greenhouse gases in the atmosphere trap and re-radiate some of the lost energy back to Earth, preventing it from losing too much heat to space and maintaining a stable temperature. This natural balance is necessary for maintaining life on Earth and preventing rapid temperature fluctuations.