The Greenhouse Effect vs. What Actually Happens in a Greenhouse

Walk into a greenhouse, as I did at Bayer's Crop Science Division in Research Triangle Park, and you will likely feel as if you are walking into an oven. It’s hot. It’s humid. And, especially if the temperature outside is cool, you are probably amazed by just how a glass or plastic covered building converts light into warmth.

It’s the “greenhouse effect” at work, right? It’s that same phenomena that is blamed for causing man-made global warming.

Well, not exactly.

The “greenhouse effect” that is warming the planet is the product of so-called greenhouse gasses in the atmosphere. Those gasses include water vapor and carbon dioxide. Those gasses allow sunlight to pass through the atmosphere to the earth’s surface. When the sunlight strikes the surface, the energy in the sunlight is converted to heat. It’s the same energy that makes you feel warm when you stand in the sun. And since those gasses do a good job of trapping much of the heat and preventing it from escaping out into space, the earth’s atmosphere warms up.

The more the amount of greenhouse gasses in the atmosphere increases, the more heat is trapped and the temperature rises.

While there are a lot of similarities with the traditional greenhouse, this is how the folks who operate Bayer’s greenhouses explain the difference.

In both cases, sunlight is allowed to pass through (greenhouse gasses in the atmosphere, glass or plastic in the greenhouse).  And in both cases, the sunlight is converted to heat.

But that’s where the similarity ends. In the atmospheric greenhouse effect, the earth warms up because the solar energy is re-radiated back towards the earth by the greenhouse gasses. Think of a ball bouncing back and forth.

But in a greenhouse, the interior air is warmed simply as a result of the heat energy from the sunlight heating up the air. The covering of the greenhouse simply prevents the heat from escaping. And since the already warm air is trapped inside as more radiation pours in, the temperature increases.

It might seem like a minor difference: It’s the energy itself that is re-radiated and prevented from escaping in the atmospheric greenhouse, while in an actual greenhouse it’s the air that has been warmed by the energy that is prevented from escaping. Now you know, "greenhouse effect" and what happens in an actual greenhouse, are actually two different things.

—Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog! 

Related Resources:


Sign Up for the Science E-Newsletter!