Posted by: graemebird | February 12, 2007

The Optimal Level Of CO2?

I don’t really have a position on this except to say that for now the optimal CO2 level is:

1. Definitely higher then it is now and:

2. Failing really great evidence just as high as it will get without imposing costs on people in the context of the massively successful spread of capitalism and no higher then that.

But on the other hand Sacha asked the question at Catallaxy and so I tried to put aside any libertarian thoughts about it and answer the question as well as I might.

From Catallaxy:


Let’s assume for the sake of argument that, everything else being equal, the Earth would gradually cool over the next few thousand years.
If carbon dioxide is a greenhouse gas and warms the Earth, what is an optimal temperature for the Earth and how much carbon dioxide and other greenhouse gases should be in the atmosphere?


For the moment I would say that the optimal CO2 level is at least 1000ppm but not as high as 2000ppm.

The optimal global temperature would be warmer on average then it is now. But not hotter in the heat of the day in the hot places.

That is to say heat differentials ought to be less.

This might imply more greenhouse but with the same level of sun power or slightly less sun power but with the greenhouse gas overmatching the reduction.

But this is not a likely scenario because the greenhouse is unlikely to overmatch any drop in solar activity.

However it may be the case that if we could keep CO2 levels elevated for hundreds of years it could mitigate against another glaciation.

I say that because I think that climate is far more serendipitous on earth then the other planets.

And whereas SEA ICE appears to me to be the ultimate greenhouse substance LAND ICE would appear to me to be the ultimate anti-greenhouse substance.

Ergo it might be that, weak though the CO2 effects are, if they can melt a few more metres of land ice every summer and retard a few more metres of land ice every winter then the net effect of that might be to save us from the ultimate disaster of another glaciation.

I say that because the effects of extra CO2 are more pronouned in the arid air.

And on this planet the arid air tends to be COLD AIR…. and so the CO2, while its effects may be too weak to detect, decade to decade, globally….

…. nonetheless over a number of centuries it could well save our asses by its effects WHERE THE WALL OF WHITE DEATH HAPPENS TO BE.

So we ought not think about any optimal temperature.

The bias is always towards catastrophic cooling.

And so if we aim at any CO2 level between 1000ppm and 2000ppm and work concientiously to get the level of aerosols down…….

…. then that might just be enough for us to get by.



  1. “What about Venus and Mars? Unlike Earth’s atmosphere, their atmospheres are about 95% CO2. But it’s not the percentage of CO2, it’s the total amount in the atmosphere. Venus has a very thick atmosphere: at the surface, the atmospheric pressure is ninety times that at Earth’s surface! You’d have to dive nearly three thousand feet into the ocean to feel the same kind of pressure. So the Venusian atmosphere is set into overdrive as far as the Greenhouse Effect is concerned, cooking its surface. The Martian atmosphere, in contrast, although nearly pure CO2, is very thin: less than 1% the pressure of Earth’s. Mars barely has any Greenhouse effect–it’s only warmed about 10F above what it would be without an atmosphere. Earth, of course, with a moderate Greenhouse Effect, is “just right.”

    So the first step in understanding the climates of Venus, Earth, and Mars, is the relative amounts of Greenhouse gases in their atmospheres: Venus has too much, Mars too little, and Earth just the right amount (in fact, water vapor, which is one percent of our atmosphere, dominates most of our Greenhouse effect—but additional CO2 can dramatically change the amount of Greenhouse effect).”
    So is it really about atmospheric pressure. He seems to have missed his own fact, that the pressure on venus is so much greater than earth’s
    How could our atmospheric pressure become like venus or mars?

  2. Jim thats it bro’.

    You have pre-empted me.

    Awhile back there was this Chinese study that came out that made that claim.

    And I was shocked and surprised but then realised that nothing that I knew contradicted the idea that air pressure is the main or at least a primary determinant of greenhouse effectiveness.

    And the idea seems inherently plausible.

    Now on this site we don’t worry about being wrong.

    We want to encourage all sorts of inductive speculation knowing in retrospect it might seem a bit embarrassing.

    But you’ve come upong some idea that is so critical. And it took these Chinese guys to remind us about it.

    I had gestated in my mind an essay called: Greenhouse Overated…….

    We can speculate here.

    And when the new and contrary information comes in that speculation is not wasted.

    On one of my threads I must thank these Chinese SCIENTISTS and apologise to them that their work was trashed by white maggot scum.

    I haven’t yet read your link but I’m sure I will soon.

  3. ok, i’ll speculate, more heat from the sun creates more air pressure this pressure keeps the co2 from escaping on venus vs less heat from sun to mars = less air pressure = less overall amount of co2!!!!!
    “In the late 1970s Michael Hart pursued the idea with a more complex computer model, and concluded that the balance was exceedingly delicate. Hardly any planets in the universe, he said, orbited in the narrow “habitable zone” around a star where life could flourish. For our solar system, the orbits in which a planet would be too close to the Sun — so that at some point the planet would suffer a runaway greenhouse effect from which it could never recover — were separated by only a 5% gap from orbits in which the planet would be so far away that runaway glaciation would freeze any ocean solid. The Earth was a lucky place, then. Hart’s calculations were riddled with untested assumptions, and many scientists denied that our situation was so extremely precarious. (Later calculations showed they were right — a Venus-type runaway on our planet is scarcely possible, even if we burn all available fossil fuels.) Hart defended his ideas energetically among his colleagues, and also in public, including an appearance on television in “Walter Cronkite’s Universe.”(9*)”

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