Photo courtesy of U.S. DOE
We often hear about the "greenhouse effect" in the negative context of global warming -- it's why the glaciers are melting and climate patterns are undergoing dangerous shifts. But the greenhouse effect is not actually a bad thing in itself -- it's a crucial and positive part of Earth's energy balance. It's what allows Earth to stay warm enough for life to survive. Without it, Earth would feel something like Mars.
The process gets its name from the greenhouses that stay nice and warm for growing plants. This is basically the same process that keeps Earth nice and warm for sustaining life. One example of the greenhouse effect that most of us experience in everyday life is the warming of a car's interior when the vehicle is left out in the sun.
You've probably noticed that your car is always much hotter inside than the outside temperature if it's been sitting there for a while. The sun's rays enter through your car's windows. Some of the heat from the sun is absorbed by the seats, the dashboard and the carpeting and floor mats. When those objects release this heat, it doesn't all get out through the windows. Some is reflected back in -- the heat radiated by the seats is a different wavelength than the light of the sun that made it through the windows in the first place, and the window glass won't let as much of that wavelength through. So a certain amount of energy is going in, and less energy is going out. The result is a gradual increase in the temperature inside your car.
Earth's greenhouse effect keeps the planet much warmer than surrounding space. In this article, we'll find out how that happens and see what's involved in maintaining Earth's energy balance. We'll also see what has happened to throw that balance out of whack.
Using the car-in-the-sun example, we can look at Earth's atmosphere as a giant, spherical car window.