Venus and a Thicker-Atmosphere Earth

(fourth post in a series dedicated to the planet Venus as “example” of runaway greenhouse warming)
Venus post #1: Venus: Cool Greenhouse?
Venus post #2: Venus Warming Revisited
Venus post #3: Venus Missing Greenhouse Warming
Venus post #4: Venus and a Thicker-Atmosphere Earth

In reply to this comment

Ok n-g I presume we can now do assuming all niceties instead of repeating our thanks so let’s try to clarify a few points.

To my mind, they act very differently

the rest of my question was “Wouldn’t moist convection for example drastically change the consequences of an increase in atmospheric CO2?”.

And the point was: when people say, look at Venus to see what GHG warming can do, the scientific answer should be that no comparison can be done with Earth as the whole mechanism of “warming” is very different (whatever CO2 may or may not be doing…if only because we have so much water vapor).

May I dare say we agree on this point?

When you’re looking at the planetary energy balance, the single number albedo is not just the starting point, but also the ending point

But surely an atmosphere, say, with low albedo in UV and high albedo to visible and IR does not behave as an atmosphere that is the other way around?

Earth’s for example is able to keep a bit warmer by the presence of UV-absorbing ozone in the stratosphere. That would mean a lower albedo in UV than in visible light, wouldn’t it?

The dry adiabatic lapse rate depends only on gravity and heat capacity

If the greenhouse effect is so strong on Venus, why isn’t the lapse rate much larger, and much larger than Earth’s, given the fact that the amount of CO2 decreases a lot between the surface and the height of 60km?

Surely the lower one gets, the more GHG there are, the higher the ability to trap heat.

Suppose there were no greenhouse effect on Venus

As you say, this is an argument, not proof

The fact that the IR emissions from Venus come from the atmosphere and not from the surface constitutes the proof

The fact that visible light comes from the atmosphere and not from the surface only proves there’s lots (lots!) of clouds on Venus. Why would the same observation regarding IR mean something else?

If the atmosphere of Earth were 100 times more massive

Let’s imagine Earth had a 10-km deep, reasonably large crater in the middle of a continent, with no liquid water on its bottom at all. What would be the temperature at the bottom of the crater? With a lapse rate for saturated air of 5.46K/km, 288+5.46*10=342K or 70C. Right? Wrong?

Venus Missing Greenhouse Warming

(third post in a series dedicated to the planet Venus as “example” of runaway greenhouse warming)
Venus post #1: Venus: Cool Greenhouse?
Venus post #2: Venus Warming Revisited
Venus post #3: Venus Missing Greenhouse Warming
Venus post #4: Venus and a Thicker-Atmosphere Earth

Let’s compute (in a simplified manner!) what would happen were Earth suddenly equipped with an atmosphere as massive as Venus’ (ie 90 times more than ours).

Given the similarities in mass and diameter of the two planets, we can assume this new atmosphere would behave similarly to Venus’, and in particular, purely adiabatically below 60km (instead of below 12km as at present).

For another simplification, let’s also imagine the new atmosphere to be just as our current one but without any water.

The lapse rate for dry Earth atmosphere is known and is 9.760 K/km.

How higher would the surface temperature be, with a dry atmosphere and a 60-km-thick troposphere?

9.760 * (60-12) = 468K higher than at present (288K)

The total for Earth is then 756K. Compare that to Venus’ surface temperature of 735K.

For an amazing coincidence, that’s 97% of the above, whilst the ratio of absorbed Solar radiation at Venus compared to Earth is… 96%.

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Note how the increase in temperature doesn’t depend on any greenhouse gas.

And so do we really need to believe in greenhouse warming when mere mass can explain the observations?

Venus Warming Revisited

(third post in a series dedicated to the planet Venus as “example” of runaway greenhouse warming)
Venus post #1: Venus: Cool Greenhouse?
Venus post #2: Venus Warming Revisited
Venus post #3: Venus Missing Greenhouse Warming
Venus post #4: Venus and a Thicker-Atmosphere Earth

In reply to Dr. John W. Nielsen-Gammon’s comment published at Eric Berger’s SciGuy blog entry “Is the global temperature now falling?“

I am the author of the Venus blog originally pointed out in a comment by Jim Mayeu.

I am all for understanding the behavior of atmospheres and the reasoning behind current scientific theories. Chances are, I have not discovered anything major, or nothing at all. But do allow me to probe this further.

(1) First question that springs to mind is, if the terrestrial and venusian atmospheres behave so differently, how could any “greenhouse effect” act similarly in both? Wouldn’t moist convection for example drastically change the consequences of an increase in atmospheric CO2?

Is it a matter then of asking people that mention Venus when talking of anthropogenic global warming, to please shut up in the name of Science?

(2) Also, the “albedo” as a single number for a whole planet is a good approximation to start from, but once again the differences between those atmospheres will surely reflect in different albedo/radiation frequency curves (not to mention how solar radiation diminishes the nearer it gets to the planetary surface).

(3) But let’s go back to the whole adiabatic business.

Lapse rates depend on gravity, and the heat capacity of the atmosphere. Gravity is similar between Venus and Earth, and CO2 responds to compression in a manner similar to air. Is that not enough to expect a similar lapse rate?

In fact, or at least in theory, the “dry” values are:

Venus: 10.468 K/km
Earth: 9.760

In practice, the Pioneer-Venus descent probes actually measured a lapse rate of 8K/km between 60 and 10km above the venusian (or shall I say, Cytherean) surface, and of around 2 between 120 and 60km.

“Under normal conditions” on Earth the lapse rate is assumed to be around 6.38, with a maximum for “dry” air of 10 and a minimum for 100% saturated air of 5.46.

(4) The “energy balance” computation you mention simply assumes a specific “greenhouse effect”. But we cannot use the thesis to demonstrate the hypothesis, so to speak.

All we know is that in terms of flux at the surface, there are 500K left to be explained.

For example, has anybody tried to compute the Earth’s surface temperature with 90-100 times more atmospheric pressure than it has, or better yet, Venus’s with 90-100 times less? (chances are, somebody has done that already). Any “greenhouse effect” would be on top, not instead of that.

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The elegance of the Fred Singer’s “explanation” recently partially revisited by John Huw Davies, a geodynamicist at Cardiff University in the UK, is after all the fact that it considers all of the Venus’ peculiarities.

Otherwise, we must imply it’s only by chance that the hottest temperatures belong to the youngest surface, in the one planet with an almost perfectly retrograde rotation (Uranus’ axial tilt is 98deg, Venus’ 177.36deg).

That’s 2.64deg away from the planet’s orbital plane’s vertical. If such a “coincidence” doesn’t scream for an explanation, I don’t know what does.

Venus: Cool Greenhouse?

(originally published as “Venus Forecast” on Aug 17. 2007):

(first post in a series dedicated to the planet Venus as “example” of runaway greenhouse warming)
Venus post #1: Venus: Cool Greenhouse?
Venus post #2: Venus Warming Revisited
Venus post #3: Venus Missing Greenhouse Warming
Venus post #4: Venus and a Thicker-Atmosphere Earth

In a few years, the old ideas of Fred Singer will come back into fashion.

Venus’ retrograde rotation, incredibly massive atmosphere and relatively young (<500 million years) surface will be elegantly explained by the crash of a massive satellite half a billion years ago (with subsequent melting of much if not the whole crust, and humongous outgassing).

UPDATE FEB 28 2008: Space.com: Venus Mysteries Blamed on Colossal Collision

Current lead-melting surface temperatures will be just as beautifully explained by simple adiabatic processes.

The role of CO2 in the heating of the atmosphere via some “greenhouse effect” will be seriously reconsidered and almost completely dismissed.

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Some quick computations:

Ratio of available solar energy Venus/Earth: 190%

Earth, surface pressure: 1000 mbar; temperature: 288K
Venus, 50km altitude pressure: 1000 mbar; temperature: 330K
330K/288K = 114% < 190%

Venus, surface pressure: 90,000 mbar; temperature: 735K
Temperature of terrestrial air compressed from 288K/1,000mbar to 90,000mbar: 887K
735K/887K = 82.9% < 190%

Far from showing any CO2-induced global warming, Venus is much cooler than expected, likely because of the high-altitude clouds that prevent us from looking at the surface.