This lesson introduces the greenhouse effect: how certain gases in an atmosphere slow the loss of heat to space. Understanding this natural process helps explain Earth's habitable temperatures and the role of human-caused climate change.
The Sun sends energy to Earth mainly as shortwave radiation, including visible light and near-infrared radiation. Much of this sunlight passes through the atmosphere and is absorbed by Earth's surface, warming it. The warmer surface then emits energy as longwave infrared radiation.
All flashcards
What is the atmospheric greenhouse effect?
The radiative effect of infrared-absorbing atmospheric constituents that absorb and emit terrestrial radiation, slowing heat loss to space.
What is the enhanced greenhouse effect?
The strengthening of the natural greenhouse effect as atmospheric greenhouse-gas concentrations increase.
What is effective emission altitude?
The weighted-average altitude from which radiation at a particular wavelength is emitted.
What is effective temperature?
The temperature an ideal uniform emitter would need to produce a specified energy flux.
How can clouds affect Earth's energy balance?
They can cool by reflecting sunlight and warm by absorbing and emitting thermal radiation; their average net effect is cooling.
Quiz questions
What does a positive value of Earth's energy imbalance indicate?Answer: Earth is gaining energy because absorbed solar radiation exceeds outgoing radiation.
Which gases are effectively transparent to longwave radiation under ordinary atmospheric conditions?Answer: Nitrogen and oxygen, which are symmetrical two-atom molecules.
What is pressure broadening in an atmosphere?Answer: Molecular collisions widen the wavelength ranges over which gases absorb radiation.
Why does Mars have a small greenhouse effect despite having much more carbon dioxide than Earth?Answer: Its atmosphere is thin, and it has little water vapor.
When the surface is warmer than the atmosphere, what is the effect of downward infrared radiation on surface heat loss?Answer: It reduces the surface's net radiative cooling without reversing net heat transfer.
Based on the Wikipedia article Greenhouse effect, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.