April 9 Science News: Key ‘geoengineering’ strategy may yield warming, not cooling

Whitening clouds by spraying them with seawater, proposed as a “technical fix” for climate change, could do more harm than good, according to research.

Whiter clouds reflect more solar energy back into space, cooling the Earth.

But a study presented at the European Geosciences Union meeting found that using water droplets of the wrong size would lead to warming, not cooling.


As science advisor John Holdren resasserted in 2009 of strategies such as space mirrors or aerosol injection, “The ‘geo-engineering’ approaches considered so far appear to be afflicted with some combination of high costs, low leverage, and a high likelihood of serious side effects.

Two major problems for most of the ‘hard’ geoengineering strategies — aka solar radiation management aka smoke and mirrors — are that they still require aggressive mitigation, and they must meet a very strong test of science.

If you don’t do aggressive greenhouse mitigation starting now, you pretty much take geo-engineering off the table as a very limited (but still dubious) add-on strategy — as even geo-engineering experts like climatologist Ken Caldeira have made clear (see Caldeira calls Lomborg’s vision “a dystopic world out of a science fiction story”).

Also, the nation and the world are not going to pursue an expensive and potentially risky strategy unless they have much higher confidence in climate science than many people seem to have today.  You’d have to know with near certainty that doing nothing would make things much worse.  Nobody undergoes chemotherapy unless the alternative is pretty darn grim and certain.

But if the entire U.S. political system ever gets that high confidence in the science, mitigation is inevitably going to be the cheaper and safer solution (Intro to climate economics: Why even strong climate action has such a low total cost).

The other problem with geo-engineering is that by the time it might seriously be on the table, say, the 2030s, when humanity has become truly desperate to avert the multiple catastrophes scientists have been warning about for decades, the planet itself will probably be warming faster and extreme weather events will be increasingly commonplace.

Thus it will be very hard to tell if your geo-engineering strategy isn’t actually making things worse.  That causes real problems if there is any scientific reason to think that your geoengineering strategy might in fact make things worse — which is certainly the case for the most plausible of all the solar radiation management ideas proposed to date, aerosol injection (see “the definitive killer objection to geoengineering as even a temporary fix”).

Now, as the BBC reports, one of the few other SRM semi-plausible ideas, cloud spraying, may also suffer from the same exact problem.

Cloud whitening was originally proposed back in 1990 by John Latham, now of the University Corporation for Atmospheric Research in Boulder, US.

It has since been developed by a number of other researchers including University of Edinburgh wave energy pioneer Stephen Salter, joining a number of other “geoengineering” techniques that would attempt either to reduce solar radiation reaching earth or absorb carbon dioxide from the air.

One version envisages specially designed ships, powered by wind, operating in areas of the ocean where reflective stratocumulus clouds are scarce.

The ships would continually spray fine jets of seawater droplets into the sky, where tiny salt crystals would act as nuclei around which water vapour would condense, producing clouds or thickening them where they already exist.

It has not yet been trialled in practice, although proponents say it ought to be.

But Kari Alterskjaer from the University of Oslo in Norway came to the European Geosciences Union (EGU) meeting in Vienna with a cautionary tale.

Her study, using observations of clouds and a computer model of the global climate, confirmed earlier findings that if cloud whitening were to be done, the best areas would be just to the west of North and South America, and to the west of Africa.

But it concluded that about 70 times more salt would have to be carried aloft than proponents have calculated.

And using droplets of the wrong size, she found, could reduce cloud cover rather than enhancing it – leading to a net warming, not the desired cooling.

“If the particles are too small, they will not brighten the clouds – instead they will influence particles that are already there, and there will be competition between them,” she told BBC News.

“Obviously the particle size is of crucial importance, not only for whether you get a positive or negative effect, but also whether particles can actually reach the clouds — if they’re too large, they just fall to the sea.”

Yet even today, any given year can be considerably warmer or cooler than the fast-rising mean.  It will be difficult if not impossible to know by the 2030s whether some cloud whitening experiment is making things better or worse.

The possibility of this technique having a warming impact has been foreseen by cloud-whitening’s developers.

In a 2002 scientific paper, Dr Latham wrote: “… the overall result could be a reduction in cloud droplet concentration, with concomitant reductions in albedo and cloud longevity, ie a warming effect”.

But, he argued, this possibility could be eliminated by careful design of the spray system.

Contacted after the presentation in Vienna, Professor Salter took the same line.

“I agree that the drop size has to be correct and that the correct value may vary according to local conditions,” he said.

“However, I am confident that we can control drop size by adjusting the frequency of an ultrasonic pressure wave which ejects drop from micro-nozzles etched in silicon.

“We can test this at very small scale in the lab.”

You can test it at a very small scale, but it just wouldn’t mean bloody much given the vastly different scale and circumstances in the real world application to achieve a meaningful impact.

One scientist at Ms Alterskjaer’s presentation, having heard her outline why it might not work, commented that it was the most depressing thing he had heard in a long time.

And Piers Forster from the UK’s University of Leeds, who is leading a major UK project on geoengineering techniques, suggested more research would be needed before cloud whitening could be considered for “prime time” use.

“The trouble is that clouds are very complicated; as soon as you start manipulating them in one way, there are a lot of different interactions,” he said.

“We need real-world data and we need modelling that tries to simulate clouds on more appropriate scales, and that means less than 100m or so, because if you look at a deck of stratocumulus it’s not one big thing, it has pockets and cells and other features.

“Far more uncertain is the idea that you’d inject a particular drop size, because it won’t stay that size for long – it will spread out, and that would be uncertain.”

The more one looks into each individual geo-engineering strategy, the less plausible it appears.

And of course, the SRM ‘solutions’ do nothing to stop the consequences of ocean acidification, which recent studies suggest will be devastating all by itself (see Geological Society: Acidifying oceans spell marine biological meltdown “by end of century”).

Even geoengineering advocate Tom Wigley is only defending “a complementary combined mitigation/geoengineering scenario, an overshoot concentration pathway where atmospheric carbon dioxide reaches 530 ppm before falling back to 450 ppm, coupled with low-intensity geoengineering,” with the goal of stabilizing global temperature rise at 2°C, in case we can’t stabilize at 450 ppm. You can see a good discussion of that at the Bulletin of Atomic Scientistsexpert roundtable response to Alan Robocks’ excellent piece, “20 reasons why geoengineering may be a bad idea.”

Well, stabilizing at 530 ppm requires doing a massive amount of mitigation starting now “” only 2 or 3 fewer wedges than what is needed for 450 (see “The full global warming solution: How the world can stabilize at 350 to 450 ppm“).

Very aggressive mitigation is the only thing that makes geo-engineering even semi-plausible (and adaptation anything other than a cruel euphemism).

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23 Responses to April 9 Science News: Key ‘geoengineering’ strategy may yield warming, not cooling

  1. Barry says:

    Excellent post, Joe.

    We already are geo-engineering the climate with CO2. Despite decades of research on it there are still unknowns about sensitivity and pacing and feedbacks. The biggest of these is how clouds behave in the short and medium term.

    Now people want to start up a second geo-engineering of our climate in a completely different manner with almost no research into it? And they are picking the least understood aspect of climate: clouds! Totally insane.

    Your insight is brilliant that humanity won’t want to gamble big on a second geo-engineering scheme until they are scared big time about the first one (aka CO2). And they won’t be scared enough about CO2 until they understand the climate science behind it well enough. Once they do they will see that the only solution is to reduce CO2 levels…not mask them.

    There is one known effective geo-engineering solution: pull out the extra fossil fuel pollution we have spilled into the air and oceans and put it back by re-sequestering it.

    Here is a recent Hansen quote on this about tar sands from a Globe and Mail article:

    “The simple message is the oil sands may appear to be gold. We do need energy and there’s a lot of potential energy in the oil sands,” Mr. Hansen said Tuesday during a break from public hearings in Sherwood Park, Alta. “But it is fool’s gold because it’s going to be clear and understood within a reasonably brief period of time that we cannot exploit unconventional fossil fuels like tar sands and tar shale. If we do, we’re going to have to suck the CO2 back out of the atmosphere and the estimated cost of doing that is $200 to $500 a tonne of carbon.”

    Wouldn’t it be so much cheaper and easier to just put a much lower price per tonne on carbon pollution today so we never have to pay so much more later?

    How about we stop our current insane geo-engineering scheme rather than start yet another one?

  2. scas says:

    I am reminded of a quote by Rajendra Pachauri in 2007:

    “If there’s no action before 2012, that’s too late. What we do in the next two to three years will determine out future. This is the defining moment.”

    When are we going to begin aggressive mitigation? I am willing to bet that many people here drive rather than take the bus or cycle, keep the house temperature comfortable rather than adjust clothing, eat meat rather than be vegetarian.

    We need leaders like Jimmy Carter who will tell people the truth and what to do, or Winston Churchill who would be frank about the nastiness of the situation and the brutish methods we need to take to keep the planet habitable.

  3. Wit's End says:

    On top of all the reasons Joe mentioned that geoengineering is a nonstarter, it also will do nothing to stop the the ozone precursor greenhouse gases from ravaging our health and environment. Lester Brown says we have to reduce CO2 by 80% by 2020. I think we had better get cracking.

    You can see the PBS documentary with him and Matt Damon here:

  4. LucAstro says:

    Now I understand why President Obama is doing nothing to prevent climate change and its urgency, because his main adviser John Holdren is telling him something like “not to worry, the solutions is… geo-engeneering and that can be done later (and by others)…”. I finally get the why of his failed presidency (see Joes articles: AND There is not much that can be done then. The US President is hooked to the perfect disinformation source (in the sense that he is given the perfect excuse to do nothing).

    What about the US CO2 emission debt? a concept that Holdren refused to acknowledge in 2009? Unless the US recognize that it is the national time-integrated CO2 emission that matters, not the daily or yearly emission, China and India are justified in not taking the US seriously and in refusing to contribute to massive CO2 emission reductions.

  5. Joan Savage says:

    Hasn’t fiddling with cloud reflectivity already been ‘tried’ on a large scale? Doesn’t everyone know the history of the west African drought and cloud reflectivity?

    The prolonged drought in the west African Sahel was correlated to particles of pollutants nucleating small water droplets that tended to stay aloft, and generating high cloud reflectivity over the Atlantic off the coast of Africa. The highly reflective small-droplet clouds cooled the ocean beneath them, reducing the evaporation rate and rain cloud formation. The Sahel suffered many years of drought. Life-giving rainfalls didn’t resume in the Sahel until after regulatory controls in the global North cut down on the atmospheric pollutants. Seems pretty highly correlated.

    Using salt to nucleate water droplets seems like it could be a re-run of that experience.

  6. adelady says:

    Geo-engineering. The only acceptable geo-engineering for my money is to accelerate geological CO2 sequestration processes to match (if only) our acceleration of CO2 release processes.

    So we just find lots of easily accessible sites where we can set up simple (or complex, but simple is better for long-term) quarrying, crushing and dispersal of suitable rocks to hasten what would otherwise be straightforward weathering. All the geo projects I’ve seen only focus on temperature – though I think painting everything white might be started now if we’re seriously worried about temperature precipitating methane release.

    But ocean acidification is every bit as serious as temperature rise and extracting CO2 is the only remedy for that.

    Personally I think that hastening weathering is not “attractive” because it’s not high-tech or glamorous in any way. But it is the only thing that we can set up to run for the _centuries_ required to absorb the CO2 already released, let alone future emissions.

  7. Nick Palmer says:

    I think reducing greenhouse gases is a desperately urgent need, but hasn’t it already been more or less established that particulate/acid gas pollution from the inefficient burning of fossil fuels from the 1940’s to the 1970’s last century was masking the warming expected from the increased CO2?

    It has been said that it was the cleaning up of emissions that allowed the underlying warming to start showing up from the 70’s onwards. If that is so, and sufficient mitigation to stabilise the greenhouse effect is sabotaged by the mad denialist movement, couldn’t we reintroduce dirty inefficiency to give us a breathing space (irony intended)?

  8. Joan Savage says:


    Let’s agree that any proposal to add particulates would not be wise to simultaneously add more greenhouse gas. Going back to dirty inefficiency would add the greenhouse gases.

    Even in the years when the global average temperature climb was partially masked by particulate effects, the CO2 concentration was continuing to creep upward in the background.

  9. DaveE says:

    Scas #2–good to hear some good words About Jimmy Carter–if Reagan hadn’t reversed his policies we would be in a better place today.

  10. Marion Delgado says:

    Pace the bullshit about people like me being “anti” geoengineering, this is one I was actively promoting looking into.

  11. Mark L says:

    Introducing geoengineering before or instead of reducing CO2 always seemed to me like – you have your hand on the hot plate – and the solution is better ways to remove the heat from your hand rather than removing your hand from the hotplate.

  12. Joe Immen says:

    6. Adelady

    I just finished reading “Fixing Climate” by Wallace Broecker and Robert Kunzig, and they conclude that mineral sequestration using ultramafic rocks is one of the best long term climate fixes.
    They say:
    • The cost of processing ultramafic rock that reacts with carbon has been estimated to be about $80 per ton of CO2—which is “five times too expensive to be practical. Mineral sequestration is thus probably still a few decades away.”
    • “Mineral sequestration has one great disadvantage. To sequester a ton of CO2, you need two tons of rock at the least.”
    • “Meanwhile, mineral sequestration has two great advantages. The first is that it is unquestionably permanent.” … “The other great advantage of mineral sequestration is that its capacity is essentially limitless. There are more than enough minable ultramafics around the world to absorb all the CO2 from all the fossil fuels we might ever burn. One particularly large deposit in oil-rich Oman is practically enough to do the job all by itself. There would be poetic justice in that.”
    • They describe mineral sequestration not as geoengineering, which usually has the goal of stabilization, but as a way of permanently cleaning up the mess we have made.

    I searched CP for mineral sequestration but not much came up, and I’m wondering what Joe thinks of its potential—is it too costly to even consider now?

  13. Lewis C says:

    LucAstro at 4/. –

    With respect, I think you are very likely doing Dr Holdren an injustice.

    To take your second point first, while I entirely agree that the US needs to acknowledge responsibility for its cumulative emissions, it has long used the denial of this need as a blocking tactic on negotiations with China, India and others. For Holdren to have acknowledged that need would have been to renounce a critically important govt policy position, which would have involved his resignation as chief science advisor to the AWOL POTUS.

    As to what advice he’s giving, I doubt very much that he’s been pushing geoengineering as the get-out once climate starts to go embarrassingly haywire – particularly given his diplomatic but notably critical public remarks on the potentials of “geoengineering approaches considered so far”, including space mirrors and sulphate aerosols.

    Axelrod and hard-nosed state department personnel with two decades invested in the policy of brinkmanship – where China is faced with intensifying threats from a destabilized climate the longer it refuses to submit to US terms – seem far more likely proponents of the undeclared national policy of total inaction to demonstrate obduracy, with easy, cheap and dirty geoengineering by sulphate aerosols as the necessary backstop option to control long-ignored climate destabilization if it became necessary.

    Personally for all it greatly preferable to sulphate aerosols, I’m not stuck on the option of cloud brightening – if its research demonstrates insuperable problems then it obviously cannot be deployed. But it is important to note that Professors Latham and Salter, who have worked on this option for most of two decades, have long been aware of the critical need for optimising droplet-size to achieve the intended results. This is a key focus of their research.

    Moreover, the option is unique in meeting numerous foreseeable criteria that effective governance of geoengineering will rightly require, including:
    – ability to monitor pilot projects’ performance within a limited area of sea;
    – ability to operate within selected optimum areas to avoid negative outcomes on societally-significant rainfall patterns, etc;
    – ability to ‘switch off’ all or parts of the program within days in the event of negative consequences arising;
    – ability to operate without any significant carbon footprint;
    – ability to operate without releasing any exotic manufactured materials into the environment, thereby precluding toxic contamination risks.

    If these potentials are compared with those of say the sulphate aerosols option, it will be noted that the latter fails all five tests very badly.

    As I see it, we were given three windows of opportunity to avoid warming the planet to the point of the interactive feedbacks become self-fuelling and accelerate beyond the possibility of control.

    The first window was in President Carter’s day, when he attempted to steer society away from raising cumulative airborne GHGs to the point of damaging interference with the climate system. Reagan’s coup closed that window.

    The second window was in President Gorbachev’s day, with the founding of the IPCC & negotiation of the UNFCCC to formulate a treaty to reduce the now damaging level of GHG outputs before their warming destabilized the great carbon banks, (forests, permafrost, clathrates, etc) and triggered the acceleration of interactive feedback loops.
    – Cheyney’s nationalistic policy of brinkmanship with China closed that window, in that even a rapid end to GHG outputs would now leave the feedbacks continuing to accelerate, due to factors including:
    the pipeline warming (reflecting our rising GHG output since ~1975);
    and the removal of the ‘temporary parasol’ of sulphate aerosols and particulates in tandem with the ending of fossil fuel burning;
    and the ongoing decline of the marine and terrestrial carbon sinks.

    The third and last window is now in play, under the notably inactive President Obama. To control the feedbacks, ending our GHG outputs is more urgent than ever, and is entirely necessary but not sufficient – As the sufficient complement to emissions control, the ongoing warming from the pipeline and the parasol must also be controlled, as must warming from the oceans that have stored the great majority of excess heat, if the feedbacks’ acceleration is to be halted while the level of airborne GHGs is steadily reduced to gradually cleanse the atmosphere.

    It seems a bitter irony that we who have striven to defend the climate for decades should now have such polarized views on the need and the means to control global temperature while the long effort for carbon recovery can take effect. Some time ago I coined the term the ‘Monbiot Fallacy’, when he assumed that Biochar would be deployed globally with a worst case set of operational codes – and using this travesty he then vilified various very senior scientists for their support of and work on the option, which, despite its critically relevant potential utility, was in his view shameful. In short, because it could be done terribly badly, it doubtless would be, and thus it was deeply wrong to promote it, regardless of its potentially critical significance.

    Whatever else Monbiot may be, he is not a scientist. Joe Romm is a scientist, as well, in my view, as being an open-minded exceptional proponent of climate defence. It thus seems reasonable to assume that perhaps like him most here would support ongoing scientific research into the cloud brightening option, given the unanswered case for additional control of warming, and the lack of any other Albido Restoration options that offer even a fraction of its merits.

    Personally I’d not support even well proven cloud brightening and carbon recovery programs unless and until there is a competent international scientific oversight capacity established, and unless and until all nations with above average per-capita GHG outputs have ratified an effective and durable climate treaty.

    But then for me the real danger of the necessary third window is not that it will be used badly to the detriment of some nations – that would be a direct illegal causus belli and simply will not be tolerated – it is that it could be abused as merely a grand offset for continued pollution if it were not fully integrated with the essential Treaty of the Atmospheric Commons.



  14. adelady says:

    Joe, I’ve seen a couple of papers on _using_ such minerals in futile endeavours such as CCS for coal-fired power plants.

    Just looking at what geologists tell us about the natural weathering processes, we have to admit up-front that we can’t do the equivalent of tectonic movement to force mountains higher – thereby exposing more rocks. But I don’t see why we shouldn’t set up a few (many) sites where wind power is used to (almost) passively chip away at suitable rock faces. The rubble should then be tumbled, crushed or pulverised, again by a suitable, self-continuing process.

    The resulting dust could just blow away or be deliberately blown higher to travel further. Gravels should just be allowed to go into water ways and tumble along to where they’ll do most good – in sea water. Or be preferentially used in unsealed roadsides, paths and the like where they will be disturbed from time to time without any real effort by anyone – and do their useful work that way.

    I really don’t see how we can release, every year, 3 million years worth of carbon previously sequestered in oil without doing _something_ geologically equivalent to counteract that. Bio-engineering through no-till agriculture, forestry, biochar and the like really impact only the carbon cycle of living things. We need to deal with the disruption to carbon’s geological cycles in rocks and oceans if we’re serious about repairing the damage we’ve done.

  15. Prokaryotes says:

    Forecaster warns of severe thunderstorms, tornadoes
    Damaging winds and large hail expected along cold front extending from Great Lakes to Southern Plains

  16. Prokaryotes says:

    Hot, dry weather stokes raging Texas wildfires
    The blazes have scorched nearly 400 square miles and almost took out the Ft. Davis National Historic Site.,0,3107932.story

  17. Prokaryotes says:

    West Antarctic warming triggered by warmer sea surface in tropical Pacific

    The Antarctic Peninsula has warmed rapidly for the last half-century or more, and recent studies have shown that an adjacent area, continental West Antarctica, has steadily warmed for at least 30 years, but scientists haven’t been sure why.

  18. mark says:

    If we don’t do enough soon enough, eventually when people are desparate enough, some faction somewhere will seize someone’s nuclear weapons for their own kneejerk attempt to cool the planet by making nuclear clouds.

    Unilateral kneejerk action didn’t work so well in this awesome tale of fiction

  19. Raul M. says:

    Now that nuclear is added to the list
    of geoengineering in progress, one
    might ask if there are any known
    life forms that physically thrive in
    an environment of nutron beams.
    I don’t recall the meek pointing to
    unusual beings that do well in radio-
    active environs. Possibly some plants?

  20. Leland Palmer says:

    Sulfate aerosol geoengineering might have to be done to keep the methane hydrates of the East Siberian Arctic Shelf (ESAS) from destabilizing catastrophically. Ocean acidification would certainly not be helped by injecting tens or hundreds of billions of tons of methane into the oceans, where a lot of it ends up metabolized into CO2 by methane consuming bacteria. The rest of the methane goes into the atmosphere, of course, where it helps fuel further positive feedback warming.

    So while geoengineering won’t help ocean acidification by burning of fossil fuels, it might help prevent catastrophic ocean acidification, and ocean anoxia, from destabilization of the methane hydrates.

    The only mild form of geoengineering that makes a lot of sense to me is Bioenergy with Carbon Capture and Storage, or BECCS. Transforming existing coal fired power plants to BECCS is technologically doable, and if a gas turbine topping cycle is added to the power plants resulting in combined cycle operation, the increased efficiency resulting from this could pay for the whole conversion.

    The combined cycle option, minus the CCS, was studied intensively by the Clinton era Combustion 2000 studies. The other half of the conversion- oxyfuel combustion and CCS- has been performed by Jupiter Oxygen Corporation, Vattenfall, and will be done at larger scale in the new conversion to CCS of the coal plant in Meredosia, Illinois.

    So, it’s doable, and it starts to put massive amounts of carbon back underground, while generating electricity at the same time. BECCS has been labeled as geoengineering, but really it is just trying to suck CO2 back out of the atmosphere, in effect. So, it’s a sort of anti-geoengineering, meant to reverse damage already done.

    With coal fired power plants, most of the cost is in the fuel. So, by increasing thermal efficiency – and saving fuel- it is possible to pay for the efficiency loss due to CCS. Oxyfuel combustion, by itself, also increases efficiency slightly, via improved heat transfer, helping to pay for the CCS. Finally biomass tends to be roughly as cheap as coal, and in many instances it is cheaper. Biomass also contains energy which can be used to drive its own conversion into charcoal- pyrolysis is an exothermic process. Excess energy produced during pyrolysis could also be used to power electrical or hydrogen powered vehicles, or vehicles run off of synthetic gasoline and diesel fuel, to harvest the biomass.

    Most coal fired power plants are located on rivers, for cooling water. In the case of Meredosia, Illinois, the power plant is located on the Illinois river, and I believe it already has unloading facilities for coal barges. Biomass plantations planted upstream of Meredosia along the river, or dried and pelletized crop waste from agriculture upstream of Meridosia, or charcoal from crop wastes, could be floated down to Meredoaia on river barges- the cheapest form of mass transport.

    Site chosen for long awaited U.S. clean coal project

    There are many, many coal fired power plants on or close to the Mississippi river system and its tributaries…hundreds, I think. The whole Mississippi river system could become one giant carbon negative BECCS operation, with the CO2 injected into such sites as Mattoon, Illinois, or into deep saline deposits.

    It is not ideal to pollute the deep underground with supercritical CO2, but I think that our fossil fuel binge has left us with no choice. If we want to get back to 400 ppm or less of CO2 in our lifetimes, we don’t have much choice except to put carbon back underground.

    If injected into the right formations, much of the CO2 could combine in situ with calcium and magnesium oxides to make limestone and dolomite, and be permanently sequestered.

  21. Nick Palmer says:

    Joan at #8

    You didn’t quite get my point. To say it another way, if the denialists look like they might end up sabotaging meaningful cuts in CO2 emissions by exploiting people’s gullibility, it would be better if we reintroduced “dirty inefficiency” as a means of neutralising the radiative imbalance until real science breaks through their foggy pseudoscience.

    It’s true, as you say, that using “dirty inefficiency” would allow CO2 to continue to accumulate (and it would of course still acidify the oceans) but that would only have to have been done because they had succeeded in delaying or stopping mitigation measures. If they succeed in preventing widespread mitigatory reduction measures, which would be far and away the most insane act ever committed by humans, we will need all the help we can get to counter what is probably to come.

  22. Flash says:

    Seeding with sodium chloride crystals wouldn’t work any better than seeding with silver iodide for the simple reason that neither scheme accounts for the the energy of condensation.
    From what I’ve been able to find out, cloud droplets grow to about 10 microns but can’t get bigger because the energy of condensation takes the form of undifferentiated surface energy rather than temperature. As a droplet grows bigger, its ratio of surface area to volume decreases. If the energy of condensation is appearing as surface energy, the surface energy per unit area increases as the droplet grows bigger. At about 10 microns in diameter its surface energy per unit area reaches a point that cannot be sustained and the droplet splits. My theory doesn’t explain why the droplets that make up a cloud maintain their small size until all at once they decide to condense into raindrops and fall. What causes the sudden change in the rules? Where does the energy of condensation go? Sometimes it may manifest as lightning, but many times I’ve seen it rain all day without any accompanying lightning or wind.
    As I’ve flown on airplanes I’ve observed that clouds are very often perfectly flat on their bottom for distances of hundreds of miles. I don’t know what that means but it could be a clue. For some reason, droplets can’t exist below the bottom of the cloud – until they suddenly and inexplicably condense into drops big enough to fall out of the cloud as rain.
    This is all by way of pointing out that cloud physics, and indeed atmospheric physics, is almost a completely unknown science. If this cockeyed and expensive scheme were tried, its result would be unknown.

  23. davidgswanger says:

    LucAstro @ 4: Like Lewis C. @ 13, I’m not sure where you’re coming from on this. The quote Joe gives does not sound like a ringing endorsement of geoengineering to me, and Holdren has sounded very concerned about it on other occasions. I think the problem is what Obama thinks is politically possible; but at least he’s stood firm on protecting the EPA from Republican attacks.

    In general, this is discouraging but not unexpected. I’m open to geoengineering, but clouds are perhaps the biggest remaining problem in climate modelling, and you would really want to understand them thoroughly before trying something like this.

    mark @ 18: The Last Ship is indeed a fine and sobering book.