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Throwing Stones at the Greenhouse Effect Fails to Hit Target

October 18, 2010

Some climate change skeptics dispute the so-called ‘greenhouse effect’, which keeps the surface temperature of the Earth approximately 30 degrees C warmer than it would be if there were no greenhouse gases in the atmosphere. In other words, without the greenhouse effect, the Earth would be largely uninhabitable.

How do we know for sure this effect is real? The principle is demonstrated through basic physics, because a bare rock orbiting the sun at the distance of the Earth should be far colder than the Earth actually is. The explanation for this observation was based on the work of John Tyndall, who discovered in 1859 that several gases, including carbon dioxide and water vapour, could trap heat. This was the first evidence for what we know now as greenhouse gases. Then, towards the end of the same century, a Swedish scientist named Svante Arrhenius proved the relationship between greenhouse gas concentrations and surface temperatures.

Empirical Evidence for the Greenhouse Effect

We only have to look to our moon for evidence of what the Earth might be like without an atmosphere that sustained the greenhouse effect. While the moon’s surface reaches 130 degrees C in direct sunlight at the equator (266 degrees F), when the sun ‘goes down’ on the moon, the temperature drops almost immediately, and plunges in several hours down to minus 110 degrees C (-166F).

Since the moon is virtually the same distance from the sun as we are, it is reasonable to ask why at night the Earth doesn’t get as cold as the moon. The answer is that, unlike the Earth, the moon has no water vapour or other greenhouse gases, because of course it has no atmosphere at all. Without our protective atmosphere and the greenhouse effect, the Earth would be as barren as our lifeless moon; without the heat trapped overnight in the atmosphere (and in the ground and oceans) our nights would be so cold that few plants or animals could survive even a single one.

The most conclusive evidence for the greenhouse effect – and the role CO2 plays – can be seen in data from the surface and from satellites. By comparing the Sun’s heat reaching the Earth with the heat leaving it, we can see that less long-wave radiation (heat) is leaving than arriving (and since the 1970s, that less and less radiation is leaving the Earth, as CO2 and equivalents build up). Since all radiation is measured by its wavelength, we can also see that the frequencies being trapped in the atmosphere are the same frequencies absorbed by greenhouse gases.

Disputing that the greenhouse effect is real is to attempt to discredit centuries of science, laws of physics and direct observation. Without the greenhouse effect, we would not even be here to argue about it.

Footnote: this post was written for SkepticalScience as part of an ongoing project to add ‘basic’ rebuttals of common climate change denial arguments. References for all statements can be found in the intermediate discussion The greenhouse effect has been falsified

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