Tuesday, July 24, 2007

Tale of Two Planets, or Three if you like

In a New York Times editorial on July 1, 2007, Al Gore said:

We — all of us — now face a universal threat. Though it is not from outside this world, it is nevertheless cosmic in scale.

Consider this tale of two planets. Earth and Venus are almost exactly the same size, and have almost exactly the same amount of carbon. The difference is that most of the carbon on Earth is in the ground — having been deposited there by various forms of life over the last 600 million years — and most of the carbon on Venus is in the atmosphere.

As a result, while the average temperature on Earth is a pleasant 59 degrees, the average temperature on Venus is 867 degrees. True, Venus is closer to the Sun than we are, but the fault is not in our star; Venus is three times hotter on average than Mercury, which is right next to the Sun. It’s the carbon dioxide.

In the Wednesday, July 18 2007 edition of the Aspen Daily News:

Gore advised the audience to compare the blue orb of the Earth to Venus, where daytime temperatures reach 867 degrees Fahrenheit and it rains sulphuric acid. The two planets have the same amount of carbon, Gore explained, but Venus’ just happens to be in the atmosphere, while most of the Earth’s is still locked underground. “The habitability of this planet for human beings really is at risk,” he said.

True Venus is very hot, (you could cook a 12 inch pizza in about 9 seconds) owing in part to a very thick atmosphere, composed mainly of CO2. And as Mr. Gore points out, Venus is closer to the Sun than Earth is. With no atmosphere, Mercury even though it is closer to the Sun, has a lower temperature. Both Venus and Earth would have much lower temperatures than Earth if they had no atmosphere. The Earth would be a cold ball of rock just a few degrees above absolute zero, Venus would likely be the same, maybe a few degrees warmer, maybe not. Actually, the Earth would be about 255K or -18C, Venus would be the same or probably warmer.

Gore says that Venus is three times hotter than Mercury. Not quite, Venus has a mean temperature of 740K (740 Celcius above absolute zero), Mercury's average temperature is 440K. For Venus to be three times hotter, it would have to be 1320K. But that's nit picking I guess, and its only math, so there's no real need for accuracy. Let's just say that Venus is really hot. The atmosphere of Venus is almost entirely CO2, the atmosphere of Earth has very little CO2, its a trace gas at about 56/100,000 of the total weight of all terrestrial atmospheric gases. Remember that CO2 is measured in parts per million here on Earth.

We should also keep in mind that the Earth has had times when CO2 levels were 10 times higher without causing a runaway greenhouse effect. Indeed, the early atmosphere of the Earth was primarily CO2 just like Venus. Perhaps owing to our distance from the sun, or to the action of microbes and formation of carbon-bearing rocks, CO2 levels fell until they were represented only as a trace. Is it possible to free enough carbon, by burning fossil fuels, to convert our atmosphere to a Venus-like state? No.

Even the normally Gore supporting realclimate.org says, "Is there a risk that anthropogenic global warming could kick the Earth into a runaway greenhouse state? Almost certainly not."
They go on to say that "The Earth may well succumb to a runaway greenhouse as the Sun continues to brighten over the next billion years or so, but the amount of CO2 we could add to the atmosphere by burning all available fossil fuel reserves would not move us significantly closer to the runaway greenhouse threshold. There are plenty of nightmares lurking in anthropogenic global warming, but the runaway greenhouse is not among them."

So, once again, Al Gore presents a picture of the future that may come true, albeit in a few billion years. So what is his reasoning behind making such outrageous claims? Just to scare people. That's the problem with AGW alarmism, people become habituated (numbed) to the tales of catastrophe, so the prophets of doom, like Mr. Gore, David Suzuki, Laurie David and others, have to present ever bigger and ever scarier stories to keep the masses interested and frightened.

Cross posted at Blue Marble Climate

Note: Thanks to eng, I stand corrected on the temperature of an airless Earth.

5 comments:

eng said...

just a few degrees above absolute zero

You mean a couple hundred degrees, i.e. 260K, which would be -13C

But I won't let that take away from your argument.

How do we know the temperature of Venus? Maybe it's just like Earth with thicker clouds so we can't see the Venusians.

John Nicklin said...

eng, without an atmosphere, Venus would be as cold as the Moon and its not -13C on the moon.

The Venusian's are real short and drink sulphuric acid martinis after work.

The temperature readings came from probes that made it a fair distance into the atmosphere before they died from melted circuit boards.

eng said...

No, you said "The Earth would be a cold ball of rock just a few degrees above absolute zero".

I think the moon is colder because it is smaller. They do claim 0 degrees Fahrenheight for earth with no atmosphere, at least nasa does.

I was being facetious of course about Venusians, but you are encouraging scepticism and encourage questioning everything. So I realized I never really read how they estimated the temperature of Venus beneath the top cloud layer.


I think the "party line" on the higher past CO2 concentration (on earth) says that the rate of increase in CO2 is much higher now and so there would be larger gyrations involved in maintaining equilibrium. A higher absolute CO2 percentage would cause more heat trapping, but if it happened over a very long time, there would be slow changes to compensate.

John Nicklin said...

Eng, good catch, I stand corrected. Earth with no atmosphere would be 255K or 255C above absolute zero. I'll have to track back to the source of the "near absolute zero" claim.

Thanks.

John Nicklin said...

And you get credit for the correction note in the post.