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

The Earth does not cool quickly despite the apparent difference in energy rates of incoming solar energy (168 watts per square meter) and outgoing radiation from the surface (390 watts per square meter) due to factors like the greenhouse effect, Earth's albedo, and heat distribution processes such as convection and latent heat. The atmosphere absorbs and traps some outgoing infrared radiation, while Earth's albedo reflects a significant amount of incoming solar energy back into space, and convection and latent heat distribute energy across the surface and atmosphere. These factors help maintain the planet's stable temperature and prevent rapid cooling.

Step-by-step solution

Identify the given values

The given values are: 1. The rate of solar energy striking Earth averages 168 watts per square meter. 2. The rate of energy radiated from Earth's surface averages 390 watts per square meter.

Analyze the energy balance

The Earth receives energy from the Sun and radiates energy back into space. To understand why the Earth does not cool quickly, we need to examine the balance between incoming solar energy and outgoing energy radiated from Earth's surface.

Factors affecting Earth's energy balance

Multiple factors contribute to Earth's stable temperature. Some of these factors are: 1. Atmosphere: The Earth's atmosphere has a critical role in maintaining the temperature balance. When solar energy enters the atmosphere, some energy is reflected back into space, while the rest reaches Earth's surface. Then, the surface radiates this energy back in the form of infrared radiation. The atmosphere acts as a blanket and absorbs part of this infrared radiation, preventing it from escaping into space. This phenomenon is known as the greenhouse effect. 2. Albedo: Albedo is the ratio of reflected and incident solar energy. Earth's average albedo is about 0.3, which means that 30% of incoming sunlight is reflected back into space. Due to the albedo, a significant amount of solar energy is never absorbed by the Earth's surface. 3. Latent heat and convection: Energy on Earth is also distributed via convection and latent heat, as warm air rises and cool air sinks, redistributing heat across the surface and also vertically in the atmosphere.

Conclusion

The planet doesn't cool quickly because of the energy balance maintained by several factors such as the atmosphere, albedo, and heat distribution processes. The greenhouse effect allows the atmosphere to absorb and trap some of the outgoing infrared radiation, while Earth's albedo and the redistribution of heat by convection and latent heat helps maintain the temperature balance. Thus, Earth does not cool quickly despite the apparent difference in energy rates of incoming solar energy and outgoing radiation from the surface.