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Understanding the greenhouse effect

From the Don Hofstrand series: Causes and consequences of a warming planet series
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The greenhouse effect is critical for life on Earth. A rocky planet like ours, this far from the sun, should be frozen solid and lifeless with an average temperature of 0 degrees Fahrenheit. In other words, it should be a big snowball floating in space. But due to the greenhouse effect, Earth’s average temperature is 57 degrees, allowing the planet to support life.

So how does the greenhouse effect warm the Earth? Sunlight passes through the atmosphere and strikes the Earth’s surface. Some of the light is absorbed by the Earth as heat and the rest is reflected back into space. The Earth’s absorbed heat is subsequently radiated back into the atmosphere. If there is nothing to stop it, the heat escapes into space.

If the atmosphere contains greenhouse (heat-trapping) gases like carbon dioxide, a portion of the Earth’s radiated heat is absorbed by these gases. The absorbed heat is then re-radiated back down to the Earth’s, warming the Earth’s surface again.

As you may suspect, the greenhouse effect gets its name from greenhouses. Greenhouses are made of glass. The glass lets sunlight into the greenhouse but blocks the resulting heat from escaping. So, even in cold weather, greenhouses stay warm.

Every time you put on clothing (or take it off), you are creating your own greenhouse effect. The additional clothing traps more of your body heat next to your body, similar to how greenhouse gases in the atmosphere trap the Earth’s heat next to the Earth’s surface.

Another analogy is your bed. Your blankets trap your body heat, keeping you warm at night. Greenhouse gases act like a blanket covering the Earth that traps heat next to the Earth’s surface.

If we get too warm during the day, we can take off our jacket. If we get to warm at night, we can take off one of the blankets. But if the Earth gets too warm, we have to learn to live with it.

Greenhouse gases are like the Earth’s thermostat. Adding more greenhouse gases to the atmosphere is like turning up the thermostat. For example, the atmosphere of Venus consists primarily of carbon dioxide (300 times more than Earth). So the greenhouse effect is very powerful. The average atmospheric temperature on Venus is 872 degrees. Hot enough to melt lead.

We are in no immediate danger of becoming another Venus. But we are in danger of upsetting nature’s thermostat and making the planet warmer and driving changes in climate.

Don Hofstrand is a retired agricultural economist from Iowa State University Extension. During the last few years of his work life, he focused on renewable energy and climate change. He and his wife live in Mason City.


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