Feb 6, 2012

The runaway greenhouse reversal: Cooling Venus

Posted by in categories: chemistry, existential risks, futurism, habitats, space

As we all know, Venus’s atmosphere & temperature makes it too hostile for colonization: 450°C temperatures and an average surface pressure almost 100 times that of Earth. Both problems are due to the size of its atmosphere — massive — and 95% of which is CO2.

The general consensus is that Venus was more like that of the Earth several billion years ago, with liquid water on the surface, but a runaway greenhouse effect may have been caused by the evaporation of the surface water and subsequent rise of greenhouse gases.

It poses not just a harsh warning of the prospects of global warming on Earth, but also a case study for how to counter such effects — reversing the runaway greenhouse effect.

I have wondered if anyone has given serious thought to chemical processes which could be set in motion on Venus to extract the carbon dioxide from the atmosphere. The most common gas in the Universe is of course hydrogen, and if sufficient quantities could be introduced to the Venusian atmosphere, with the appropriate catalysts, could the carbon dioxide in the atmosphere be eventually reversed back into solid carbon compounds, water vapor and oxygen? The effect of this would of course not only bring down the temperature, but return the surface pressure, with 95% of its atmosphere removed, to one more similar to that of Earth. Perhaps in adding other aerosols the temperatures could be reduced further and avoid a re-runaway effect.

I’d like to hear others thoughts on this. It would be a long term project — but would perhaps make our closest planet our most habitable one in the future — one we could turn into a habitat that would be very accessible, with ample oxygen, water and mineral resources… The study of such a process would also greatly benefit Earth in the event that theorized runaway greenhouse effects start to occur on our own planet, the strategies learned could save it. Other issues to address regarding Venus: lack of magnetic field and its slow rotation would have to be considered, though hardly off-putting, and 150ppm sulfur dioxide in the atmosphere would need to be cleansed — surely not insurmountable.


Comments — comments are now closed.

  1. Ray Wright says:

    Prompted by an article I saw in a science magazine about cooling Venus, about 30 years ago, I collaborated with a colleague of mine to work out how long it would take the surface layer of rock on Venus to cool down to 20 deg C, if one could remove the Venusian greenhouse effect at a stroke. The result was not encouraging — about 1 million years. The original article proposed seeding the Venusian atmosphere with algae, to absorb the carbon dioxide, but water is required too, and the Venusian atmosphere is too dry, so you would need to crash an ocean’s worth of water into Venus, using Oort Cloud or Kuyper Belt objects, to bring back all the water needed for a terrestrial environment. That would not be unimaginably impossible, but there’s little one can do to improve the cooling rate, given that rock has the thermal conductivity that it has. Even the original article about using algae estimated that 20,000 years would be needed for the surface to become habitable, but that left out the cooling rate problem. It’s a pity, but we’ll have to forget about terraforming Venus without magic. There’s no reason why we couldn’t have manned station in Venus orbit and even habitation platforms floating high in the atmosphere, though.

  2. Tom Kerwick says:

    Ray — thanks for the feedback. That 1 million year cycle to cool the surface rock to 20°C seems quite incredible — is that a linear trajectory? How can molten rock on Earth cool so much quicker — were the calculations based on a slowly cooling 450°C atmosphere?

    I was considering what the effects of more direct approachs than seeding the atmoshpere with algae would be. What would happen if liquid hydrogen was gradually introduced in a controlled manner with the right catalysts — could the CO2 be converted back into carbon and water? Or would you just get methanol? Is there something more appropriate that could be introduced to do this?

    I know we can talk of 20,000 years as a long time, but not in the general lifetime of the Earth, assuming humanity doesn’t completely screw up our planet — despite our best efforts. All in all, options like the Moon and Mars of course pose more immediate options for colonisation, but I was wondering if Venus is a real opportunity that could prove more the attractive in the long term if we could tame her — A long shot though.

  3. I enjoy reading about these grand solutions, for they make you think. All my recent books are entitled SIMPLE SOLUTIONS, but, of course, they are anything but.

    Anyway, fine to talk about it, but the reality is that this one is not worthy of serious consideration. When you ask what for, how, how long and how much, the exercise becomes ludicrous. Maybe I’ve become too much the isolationist, as I thought the International Space Station was a waste of money and I’ve long argued that we should pull 90% of our military out of those 150 countries:

    As you might know, one of the chapters from my SIMPLE SOLUTIONS for Planet Earth is entitled, “The Venus Syndrome.” I have a couple of Huffiington Post articles on this very subject:…06120.html

    the first one being almost four years ago when I got frustrated that compelling logic was not working on decision-makers, so, I thought, maybe fear can be more effective. I’m actually taking this concept to another level with an upcoming novel on the theme…then, who knows, maybe a best-seller and movie? A few stand alone postings did not make any ripple, but maybe that movie might become the difference maker. Otherwise, global warming will become yet another issue where this fatal flaw of our society–not being able to make a decision until it is too late–prevails. Unfortunately, this one could be fatal to Humanity on Planet Earth.

  4. I am always concerned with the proposal of a one dimensional solution to a four dimensional problem as we have here. The chemical changes are interesting. But this proposal would be at a single place. The Venus problem affects the entire rotating planet, so how do you make the proceed solution work for the entire planet? As the planet rotates, the external heating effects will vary in different locations and the associated temperature gradients will create pressure changes and therefore local winds. The locally varying winds affect the chemical mixing so that the suggested solution will also be different all over the planet and not have the uniformity required by the suggested proposal. FurthermoreI doubt whether the suggested proposal would produce a stable atmosphere.
    I do not consider the proposal offers a workable solution for reversing the runaway Greenhouse effect we witness on Venus.

  5. Brock says:

    Point of order: Venus’s atmosphere & temperature makes its SURFACE too hostile for colonization. The cloud deck at 50 km altitude is very nearly the most hospitable extra-terrestrial location in the solar system. Perhaps THE most hospitable. A thin coat of glass, or some other substance that protects from the sulfuric acid in the atmosphere is all you need. And a valve leak when the outside air pressure is the same as the inner pressure is much less disastrous than on Mars or the Moon.

    To ask a question: What would happen if we captured a carbonaceous asteroid, and spun out a giant sun shade between Venus and the sun? How much would that speed up its cooling down, if it was subject to eternal night? We could crash an ocean’s worth of water into it later, when the sun shade had done its work.

    Later (much later) when the atmosphere had cooled and the oceans were liquid again the sun shade could be replaced with a difractor that reduced the amount of sunlight reaching Venus to something more Earth-normal, to keep it from becoming too hot again.

    Of course, it may all be a moot point if the Super-AI nanobots consume Venus and build a Dyson bubble out of it.

  6. Paul Werbos says:

    Fr decades, people have talked about bioengineering some kind of archaea to live in the (high) atmosphere of Venus, to try to initiate some kind of carbon fixation. But if they end up sinking to the surface, would it be unstable (fires)? Is there hope of binding it to something else (like the calcium which has been crucial to earth)? Perhaps if we ever move further out into the solar system, skimming the atmosphere of venus for our own use might have some possibilities.
    Not exactly this week’s project… part of Life Form Designs and Extreme Ecology, fields at a very early stage right now.

  7. JohnHunt says:

    The sunshade idea seems to have merit although again it would probably still take an inordinate amount or time to cool. But if looking for an engineering solution, why MUST we get things across the entire surface of Venus to Earth-like conditions? If we allow paraterraforming then the issues becomes, can we make a cool surface on top of that hot surface? Can we make pressure vessels so that we get 1 arm of pressure in the living spaces, and can we produce a breathable environment. I think that the answer to all of those is yes. Keep expanding the paraterraformed areas until it covers the surfaceof Venus.

  8. Tom Kerwick says:

    That’s a good point John, works with anything in progressive design — ‘start small, think big’. I think it is especially applicable to a tentative topic such as space colonization.

  9. Point of order: Venus’s atmosphere & temperature makes its SURFACE too hostile for colonization. The cloud deck at 50 km altitude is very nearly the most hospitable extra-terrestrial location in the solar system. Perhaps THE most hospitable. A thin coat of glass, or some other substance that protects from the sulfuric acid in the atmosphere is all you need. And a valve leak when the outside air pressure is the same as the inner pressure is much less disastrous than on Mars or the Moon.

    Serendipitously enough, I was just reading a recent sf novella that uses exactly this trope for its backdrop: “The Sultan Of The Clouds” by Geoffrey Landis. Not the most original story, perhaps, but the Venusian cloud civilisation is a pretty slick bit of worldbuilding. :)

  10. (Ah, apologies; first para of comment above was meant to be a blockquote, didn’t realise the comment field here doesn’t parse HTML. :) )

  11. I admit that I’m just a twelfth-grader interested in science, but I have something to say on the subject of terraforming Venus.

    I suppose one could dream of some grand leverage or force to move Venus to an orbit opposite earth, but then, that may take some improvements in technology. I agree with the shade idea between the sun and Venus in combination with other ideas like elevating water from a moon of Jupiter called Europa (of course we may find life on Europa), or maybe Saturn’s moon Titan, or the Kuiper Belt to propel to Venus.…not to mention, taraforming Mars. Maybe this way we could first do something to change the chemistry of the problem. Then we could use incredibly huge fussion bombs from earth further breaking down CO2 and sulfur deoxide. Than make use of self-replicating lime producing nanobots to begin recovering from acid deposition.

    Should we rocket a huge fussion bomb to Venus for a test? What’s to lose? Let’s get a real test! World knows we got plenty skill at making fussion bombs.

    Furthermore, could more water from comets/Europa, etc. help cool Venus? I’m a can-do person. I believe that taraforming Mars may be the first effort, but we will taraform Venus if we need or want to.