Is the term "Greenhouse Effect" a bad analogy?

Question

Greenhouses work because the solar radiation is absorbed by opaque objects (or the ground) inside the glass, and the warm air comming off the warm objects can't rise past the roof. Presumably if a greenhouse were tall enough, it wouldn't get warm inside.

Doesn't the global warming theory say that carbondioxide has a higher opacity than the oxygen it displaces, and will absorb radiation given off by the sun and the earth.

Is CO2 supposedly more like a dust cloud than a pane of glass?

Answer 1

It can be considered a poor analogy because the main reason a greenhouse is so much warmer is not the trapping of the infrared radiation, but the almost complete lack of advection (horizontal transfer of energy) which is a major cooling phenomena.

Think about what happens when you walk into a greenhouse, there is almost no air movement, and wind (horizontal air movement, advection) is a cooling phenomena.

Answer 2

How a greenhouse works: A greenhouse is fairly simple to explain, using the terminology presented in the last lesson. The glass walls and ceiling of the greenhouse transmit the visible light energy entering the greenhouse from the sky. Much of this energy is absorbed by the plants and other objects in the greenhouse. These objects later emit some of this absorbed energy as infrared energy. Although this infrared energy can escape the greenhouse, the pockets of air that have been heated cannot, so the greenhouse gets warmer. To use scientific terminology, the glass of the greenhouse allows the infrared energy to radiate back to the atmosphere, but it does not allow the warmed air to convect out of the greenhouse.

How the "greenhouse effect" works: First of all, only some gases in the atmosphere interact with outgoing infrared energy from the Earth. These include carbon dioxide, methane, nitrous oxide, and others, which are frequently called "greenhouse gases." Similar to a greenhouse, light energy enters the atmosphere from the Sun. Most of it passes to the ground, where it is either reflected or absorbed by the water, plants, buildings, and so on. The reflected energy passes back into space without changing. Some of the absorbed energy is later emitted as infrared energy. (Again, this is similar to the plants in the greenhouse.)

However, greenhouse gases interact differently with the infrared energy than the glass of the greenhouse does as the energy is trying to escape. The gases absorb the infrared energy emitted by the Earth's surface. Having absorbed this energy, the gases tend to move faster—the light energy is converted to kinetic energy. Then, they emit some of this extra energy as infrared light energy. The direction in which this energy is emitted is random. Sometimes the emitted energy travels back down towards Earth's surface, which adds heat to the air near the surface. Sometimes the emitted energy goes straight into space. It is quite likely that the energy emitted by one greenhouse gas will be absorbed by another. Therefore, as more greenhouse gases are added to the atmosphere, less energy is returning to space, and more energy is being absorbed and then emitted by the greenhouse gases.

Answer 3

By and large it's a good analogy...

A GREENHOUSE
A greenhouse is fairly simple to explain. The glass walls and ceiling of the greenhouse transmit the visible light energy entering the greenhouse from the sky. Much of this energy is absorbed by the plants and other objects in the greenhouse. These objects later emit some of this absorbed energy as infrared energy. Although this infrared energy can escape the greenhouse, the pockets of air that have been heated cannot, so the greenhouse gets warmer. To use scientific terminology, the glass of the greenhouse allows the infrared energy to radiate back to the atmosphere, but it does not allow the warmed air to convect out of the greenhouse.

THE GREENHOUSE EFFECT
First of all, only some gases in the atmosphere interact with outgoing infrared energy from the Earth. These include carbon dioxide, methane, nitrous oxide, and others, which are frequently called "greenhouse gases." Similar to a greenhouse, light energy enters the atmosphere from the Sun. Most of it passes to the ground, where it is either reflected or absorbed by the water, plants, buildings, and so on. The reflected energy passes back into space without changing. Some of the absorbed energy is later emitted as infrared energy. (Again, this is similar to the plants in the greenhouse.)

THE DIFFERENCE
Greenhouse gases interact differently with the infrared energy than the glass of the greenhouse does as the energy is trying to escape. The gases absorb the infrared energy emitted by the Earth's surface. Having absorbed this energy, the gases tend to move faster—the light energy is converted to kinetic energy. Then, they emit some of this extra energy as infrared light energy. The direction in which this energy is emitted is random. Sometimes the emitted energy travels back down towards Earth's surface, which adds heat to the air near the surface. Sometimes the emitted energy goes straight into space. It is quite likely that the energy emitted by one greenhouse gas will be absorbed by another. Therefore, as more greenhouse gases are added to the atmosphere, less energy is returning to space, and more energy is being absorbed and then emitted by the greenhouse gases.

Answer 4

Building A Greenhouse Plans Easiest!

Answer 5

My favorite is in response to the argument that climate changed naturally in the past, therefore humans can't be causing current climate change. The analogy is that according to this logic, since forest fires were always caused naturally in the past, that humans can't cause forest fires. I came up with another one the other day. The new in vogue argument for "skeptics" is that the atmospheric CO2 increase is natural, not anthropogenic. My analogy is that this is equivalent to arguing that the Sun revolves around the Earth. We know it's wrong, we know why it's wrong, and we've known this for ages. If somebody tells you the Sun revolves around the Earth, your reaction should not be "wow, this could revolutionize the entire field of astrophysics!", your reaction should be "no, unless you produce some absolutely extraordinary evidence, that's obviously wrong."

Answer 6

It is not a bad analogy, It was coined long ago and designed so that the general public could get a grasp on what was happening, without needing to go into the science, which is a waste of time for most of the population. I think it has done pretty well.

It seems largely to have given way to climate change, perhaps because the idea of a couple of degrees extra doesn'r sound bad to some people, but more likely to sugest the changing and stormy weather we're in for, more people will relate to it as a problem, again, without going into the science.

FoE are now calling it "Climate Chaos" which better reflects the unknowable and turmultuous climate changes we have coming our way.

Of course, some will insist in trying to 'grapple' with the science, but I doubt there is any analogy that would have or will ever bring them round.

Answer 7

Not only is "Greenhouse Effect" a bad analogy, it is apparently a bad theory all the way around. If you look at the Vostok ice core data (see reference) there is a consistent behavior for every temperature peak shown. That is, after every temperature peak the temperature falls before the carbon dioxide concentration does. If the "Greenhouse Effect" were valid, then it would be impossible for the temperature to consistently decline while carbon dioxide levels remained elevated.

Another indication that the "Greenhouse Effect" theory is flawed is that if it is applied to every planet in the solar system it never provides the correct temperature. If, instead, one uses the simple Blackbody calculation which ignores any atmospheric effects, one obtains accurate temperature predictions for every planet with the exception of Venus.

Venus is special in that it emits more energy than it absorbs. This cannot be due to a "Greenhouse Effect" since the only energy source in that model is the sun. So, Venus must still be cooling from some recent event such as a large meteor or comet impact. The important thing is that the "Greenhouse" model doesn't give accurate answers while ignoring any atmospheric contribution does.

Answer 8

No--the analogy is more than an analogy--the same basic principle is at work. Namely that it acts as a trap--heat, oncen inside the system (Earth's atmosphere) can't escape because the CO2 traps it. The difference is only in the compositon of the heat trapping barrier--carbon dioxide instead of glass.