The Real ‘Inconvenient Truth’

Given the number of JunkScience.com readers expressing some confusion over the “greenhouse effect,” carbon dioxide, global warming and climate change, we thought it might be a good idea to pull together a page of questions-and-answers, complete with a few nice little graphics explaining the facts.

We thought that since there is long-standing, intense public interest in these topics and that vast sums of public and private monies are being thrown at the much-dreaded “problem” of “global warming,” there should be a wealth of quality explanations and graphics to which we can point readers to alleviate their confusion.

That was about the time that our quick project and quiet weekend went awry very quickly.

Who would have thought so many “issue” sites, environment sites and, yes, government sites, could be hosting so much utter garbage on a topic subject to such intense scrutiny? Who could have imagined having to spend several hours wading through searches to find a few simple graphics correctly expressing the greenhouse effect? Who knew that so many blowhards are out there pontificating from complete ignorance?

Some of the bad descriptions appear to be poor efforts at simplifying the material to suit grade-school course work and the like, but that does not make them any more acceptable. Obviously a slight rethink of this project was necessary. We will now try to deliver an extremely simplified version of how this greenhouse thing actually works and some indication of what might be expected from what is known about the Earth and what has been measured, rather than simply guessed about.

Basic misconceptions that must be addressed include:

Does the Earth’s atmosphere primarily behave like an actual greenhouse?

No. The term “greenhouse effect” is unfortunate since it often results in a totally false impression of the activity of so-called “greenhouse gases.” An actual greenhouse works as a physical barrier to convection (the transfer of heat by currents in a fluid) while the atmosphere facilitates convection. So-called “greenhouse gases” in the Earth’s atmosphere do not act as a barrier to convection so the impression of actual greenhouse-like activity in the Earth’s atmosphere is wrong.

For an expanded description of physical greenhouses see Sue Ann Bowling’s ASF piece.

Supplemental, April 25: A couple of people have written challenging whether physical greenhouses function as convection barriers since they do radiate and so does the atmosphere – apparently we need to expand on this point. To begin with, a physical greenhouse is simply a contained subset of the atmosphere – it is not bounded by the near-vacuum of space as is the planet’s atmosphere and so has rather different properties. The proof that convection containment is critical to the function of physical greenhouses is that it is possible to create structures with similar radiative properties, one which allows convective activity between the structure and unconstrained atmosphere and one which does not. Only the structure constraining internal-external convection will function as an effective greenhouse. Greenhouse gases categorically do not inhibit convective activity and so are not like a physical greenhouse.

Forgetting about the unfortunate-but-commonly-used terminology for a moment, is the so-called ‘greenhouse effect’ bad?

Only if you think undesirable a habitable planet with relatively stable temperature. Our moon, lacking greenhouse effect, makes a kind of comparison even though lack of atmosphere makes it uninhabitable regardless of temperature. The moon’s mean surface temperature by day is 107°C (225°F) and by night drops to -153°C (-243°F). The Lunar temperature increases about 260°C from just before dawn to Lunar noon. So, if you fancy such a temperature range then a greenhouse effect-free world is for you; otherwise, you might want to be pleased we have it here on Earth.

For the rest of this well-researched story and the accompanying graphics,
please click on www.junkscience.com/greenhouse.