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Climate engineering

December 6th, 2007 by Jamison A. Smith, Ph. D. · 8 Comments

For journal club this week, I discussed an editorial about climate engineering [Crutzen, 2006] and a response to  this editorial [Bengsston, 2006].

Crutzen proposes injecting SO2 into the stratosphere to counteract global warming caused by the combustion of fossil fuels.  The SO2 should oxidize to form sulfuric acid, and this acid will condense to form aerosol that scatter incoming solar radiation, thus providing a cooling effect.

The proposal appeared to be feasible and effective.  My strongest criticism of the proposal was that the climate-control aerosol will destroy stratospheric ozone.

Bengtsson [2006] provided a few extra criticisms. Two of the strongest criticisms were:

1) We’d have to keep injecting this SO2 every year for centuries until the atmospheric CO2 concentration recovered back to preindustrial values.

2) The acidification of the ocean from the dissolution of excess CO2 would result in undersaturation of minerals in the ocean. I think this undersaturation would result in the dissolution of carbonate animal remains which would shut down the burial of C in the ocean sediments, thus providing a positive climate feedback to CO2, but Bengtsson didn’t actually explicitly state this positive feedback.

I think oceanic acidification would result in other problems as well, like maiming or killing oceanic biota.

- Jamison A. Smith, Ph. D., December 6, 2007

Tags: aerosols · ATOC Journal Club

8 responses so far ↓

  • 1 Hank Roberts // Dec 11, 2007 at 8:54 am

    …Very little is known about how these clouds form over the poles, why they are being seen more frequently and at lower latitudes than ever before, or why they have been growing brighter. AIM will observe two complete cloud seasons over both poles, documenting an entire life cycle of the shiny clouds for the first time.

    “It is clear that these clouds are changing, a sign that a part of our atmosphere is changing and we do not understand how, why or what it means,” stated AIM principal investigator James Russell III of Hampton University, Hampton, Va. “These observations suggest a connection with global change in the lower atmosphere and could represent an early warning that our Earth environment is being changed.”
    —-end excerpt——

    So — the engineering’s going on now, eh? Reminds me of Stewart Brand’s line from the old Whole Earth Catalog:

    “… might as well get good at it.”

  • 2 joe-6-pack // Jan 24, 2008 at 6:02 pm

    Forgive me, it has been years since my Oceanography and Carbonate Petrography courses…

    Regarding the concern over oceanic acidification, if the atmosphere is warming, shouldn’t we assume the oceans are warming also? And if the oceans are warming, won’t they be emitting more carbon dioxide, rather than absorbing it? And wouldn’t the loss of oceanic carbon dioxide result in a deepening of the CCD, resulting perhaps in more shallow-water limestone deposition?

  • 3 joe-6-pack // Jan 24, 2008 at 6:03 pm

    Oops, I meant Carbonate Petrology…

  • 4 Sean Davis // Jan 27, 2008 at 11:12 am


    You are somewhat correct. As the atmosphere warms, so warms the ocean. As you may recall from basic chemistry, the solubility of CO2 in a liquid (such as the ocean) decreases with increasing temperature.

    This is one of the longer-term positive feedback mechanisms for climate change — i.e., increase CO2 in atmosphere-> increase temperature of ocean-> ocean absorbs less CO2 -> CO2 concentration in atmosphere is increased.

    However, I think the most appropriate way to look at this is that the ocean is constantly gobbling up CO2 from the atmosphere and ‘spitting’ it out in the form of sediments. Oceanic warming and (I think — I’d have to double check) acidification both act to slow down this process.

  • 5 Jamison Smith // Jan 27, 2008 at 12:42 pm

    Hi Sean,

    Good work.

    The solubility of CO2 in water decreases with increasing temperature. The ocean, however, is undersaturated with respect to CO2 dissolution and hopefully will remain that way.

    CO2 is the acid present in water. Fresh water has a pH of 5-5.5 because of CO2 dissolution. Ocean water has a pH of 8ish and it has been falling because of anthropogenic CO2 production.

  • 6 joe-6-pack // Jan 27, 2008 at 6:24 pm

    Back to the scientific issue of ocean pH.

    “CO2 is the acid present in water. Fresh water has a pH of 5-5.5 because of CO2 dissolution. Ocean water has a pH of 8ish and it has been falling because of anthropogenic CO2 production.”

    What about the contributions of other acids as part of water pH? What about sources of oceanic carbon dioxide other than the atmosphere, e.g., submarine volcanoes, brine vents (where present), black smokers,…?

    As for fresh water, there are other acids that may be “in play” from rotting vegetation and the dissolution of sulfide (and other) minerals, especially where soil, sediments and rock have been disturbed by farming, construction, mining,…

    I have seen a pH of 4.5 (+/-) in a Georgia stream draining a small swamp. There was nothing else that we could see in the drainage basin beside the swamp. We were so surprised that we sampled it several times and obtained the same results.

    Back to the issue of falling oceanic pH values. How long have we been able to measure them with a sense of accuracy? How do we know that what we are seeing is not just part of a natural cycle?

    Climate study is a work-in-progress and utilizing the concept of Multiple Working Hypotheses is an important way of lessening the effects of personal bias. So often in the wild world of nature, there is more than one reason for something happening.

    My bias is that of a field geologist who has spent hours in conversation with other field geologists as to the “hows” and “whys” of what we see and measure, even when it doesn’t seem to make any sense. And if a “pat” answer doesn’t reveal itself, we have to consider alternate possibilities and explanations when schedule and budget constraints prevent the completion of that perfect, completed study.

    Yeah, we skeptics ask too many messy questions. If you give plausible, thoughtful answers, we might be convinced.

  • 7 Sean Davis // Jan 27, 2008 at 8:54 pm


    For a thorough introduction on ocean acidification and its causes, I suggest this realclimate article.

    Your point above about fresh water is irrelevant. Jamie’s point about fresh water having a pH of 5 is that with 380 ppmv of CO2 in the atmosphere, you will get fresh water of that pH. Put a glass of distilled water out (with ph 7), leave it for a week, and it will have a pH of 5 (or whatever the exact value is). That has nothing to do with anthropogenic climate change per se.

    For the ocean issue, there is really no question that that the pH has gone down, and that it has gone down because of the increase in atmospheric CO2 — not vents or any exotic mechanism as you propose above.

    This is a topic that you can read about on your own a number of different places, including high school and undergraduate textbooks on chemistry or Earth Science — not to mention plenty of peer-reviewed research. This is not new science by any stretch of the imagination.

    As for your specific questions above,

    1. I don’t know when reliable ocean pH records started. That’s a good question.
    2. What specific “natural” mechanisms are your asking about or proposing that would reduce the oceanic acidity and meet the following criteria:

    a) be big enough to actually matter, b) explain the acidification better than increasing atmospheric CO2, and c) explain why the predicted decrease in pH from the well-documented increase in atmospheric CO2 WOULDN’T happen.

    Did you have something in mind?

  • 8 joe-6-pack // Jan 27, 2008 at 10:35 pm

    As for the radiative transfer class, when compared to the effects of atmospheric water vapor and water droplets, you are still addressing a small component. What about the radiative transfer values of water vapor and water droplets?

    And what “commits” us to a 1 meter sea level rise? Computer models? Only time will tell if it will happen.

    On a longer-term scale, why did the Earth rebound from the temperatures at the end of the Pleistocene or from the individual glaciation events during the Pleistocene? Why did the Earth rebound from the Dark Ages Cold Period or the Little Ice Age?

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