Study: Geoengineering Can't Adjust Earth's Thermostat to Everyone's Liking

By Andrew Moseman | July 19, 2010 11:34 am

Planet earthSchemes to hack the planet and save us from global warming have two layers of obstacles to overcome. First, is it technologically and physically possible to do what’s proposed? And then there’s the second: Is it politically possible to tinker with the planet?

Those who would argue “absolutely not” to the latter got a boost by a new study out in Nature Geoscience. Katharine Ricke and her team modeled the effects of one of the most popular geoengineering plans: seeding the atmosphere with aerosols to reflect away some of the sun’s rays, mimicking the way a massive volcanic eruption can cool the Earth. Ricke found that the effects on rainfall and temperature could vary wildly by region—and that what’s best for one country could spell disaster for another.

For example, Ricke says, her study found that levels of sulphate that kept China closest to its baseline climate were so high that they made India cold and wet. Those that were best for India caused China to overheat. She notes, however, that both countries fared better either way than under a no-geoengineering policy [Nature].

Given the complex connectivity of the climate system, it’s not possible to fix everything to everybody’s liking. While the team’s study shows that geoengineers could control either temperature or precipitation pretty well by fine-tuning their atmospheric seeding, they couldn’t control both at once.

“People won’t agree on what level of geoengineering is desirable,” says Myles Allen of the University of Oxford, who was involved in the study. “It works, but it won’t work the same way for everyone” [New Scientist].

Nevertheless, the drumbeat for geoengineering isn’t quieting. Two books that came out this spring, Jeff Goodell’s “How To Cool the Planet” and Eli Kintisch’s “Hack the Planet”, delved into the idea. Several more out this year try to predict what the Earth will be like in the warmer future, and whether you should go ahead and buy that summer vacation property in Canada. Last September Britain’s Royal Society issued a report calling for investment in geoengineering as a backup plan in case nations fail to constrain their emissions. And that was before the failure of the Copenhagen climate summit.

But, as climate models improve, scientists could get a better picture of the fallout from such a dramatic action as seeding the atmosphere with aerosols, according to climate guru Ken Caldeira.

“I don’t think climate modelling is at the point where we should trust one single model at that scale,” Caldeira says. “But I think the results are robust in the sense that it’s the kind of issue that people will need to face. The qualitative idea is that you’re going to have differential results in different regions, and that’s going to cause people to want different amounts of this stuff up there, if they want any of it up there at all” [Nature].

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Image: iStockphoto

  • FUAG

    “kept China closest to its baseline climate” – What exactly does “baseline climate” mean? It’s temperature during the last ice age? This type of language is what causes skeptics to dismiss scientist rhetoric. If someone can throw around a term like “baseline climate” as if there is actually any way to determine what that is, how can any other absolute statement be trusted. Is baseline climate based on an average? Is that an average over a time span, and if so what time span? 10 years? 100 years? 100 million years?….

  • Steve Harris

    We really don’t have to do this with aerosols. Sunlight can be reflected off white plastic, preferably something that biodegrades and leaves behind some kind of harmless white pigment like titanium dioxide.

    People have suggested dumping ping pong balls in the ocean, but this kind of thing will just float around and gum things up. We’d really rather have the plastic on land where we can watch it. The two obvious places are the Sahara (some parts of which don’t even have plantlife), and the other place is the world’s ice-sheets. It’s already been shown that plastic covered ice melts more slowly than naked ice. The problem is getting the plastic out there.

    The amount of sunlight we need to reflect to make up for the CO2 increase (at least energywise—this won’t fix ocean acid) is 2% of the total. So we’d have to increase the albedo of places like the Sahara (0.4, meaning it reflects only 40% of sunlight) to something like 0.9, meaning it reflects 90%, and do that for 4% of the Earth’s surface. That would be 20 million km^2, or about twice the area of the Sahara. But there are lots of other land areas, including all that ice.

    The cheapest way to get plastic inland is to wait for the wind to blow in the right direction, and waft it in, as lighter than air balloons. Each would have a single-hoop stiffener to make sure the plastic stays flat and spread-out when the balloon lands and eventually collapses. With a little practice, you could land these anyplace one wanted, for the cost of transporting them to the coast by ship and inflating them.

    These balloons could be filled with any gas—they could even be hot air balloons, but the cheapest method is probably hydrogen. Hydrogen is available for less than half the price of natural gas (per volume) and has twice the lifting power, and this factor of 5 in efficiency probably makes up for the difficulties in transporting it by ship. (It is prohibitively expensive to make hydrogen electrically, even with nuclear powered ships)

    Here’s an exercise for the student: Show that since water is roughly 833 time as dense as density of (air-hydrogen), that the needed diameter D of a hydrogen balloon made of plastic with thickness t and specific gravity S (water =1) is given by:

    D = 5000 * S * t

    Thus, if S = 2 (plastic twice as dense as water, including the titanium dioxide), and t is 1 millimeter, the balloons need to be about 5000 * 2* 0.001 meter = 10 meters, for a radius of 5 meters. When these collapse, you get a circular plastic tarp about pi R^2 = 78.5 m^2. If the stiffener hoop can be rigged to expand as the balloon collapses, you can get the maximal area of half the total balloon surface (since it’s a double layer), which is twice the previous figure (exercise again for the student). A surface of 20 million km^2 would take 127 billion of these, if they don’t overlap. It would take 7 x 10^13 m^3 of hydrogen to inflate them. This is 5 trillion dollars of hydrogen, not counting transportation costs. For the lift-gas to cost more than 20 million km^2 of double-thickness plastic, the plastic would need to cost less than 13 cents a square meter.

    The major cost here is probably still the 40 to 100 million km^2 of titanium dioxide impregnated plastic. If anybody has an estimate for this, I’d be curious. I would suppose that this project will cost on the order of a US $20 trillion dollars if the cost of the plastic is comparable with the hydrogen and the other program costs are twice the material costs (compare with the global GDP of perhaps $30 trillion).

    Before anybody laughs out of hand at such figures, I suggest comparison with some other suggested methods of cooling the Earth by reflecting sunlight. First of all, a plastic sheet put onto ice-sheet or desert is far, far, cheaper to place by any method (even helicopter) than putting it into space (orbit). And the difference in efficiency between white plastic and metalized plastic is not that great. The surface areas given are how much surface area you need, no matter how you do it, or where you put your material (in space or on land or ice). Even at $1000/kg to get into orbit (10% of present prices), the costs above go up by a factor of 10, at least.

    Furthermore, film mirrors in orbit have a problem which has not been addressed, which is that the pressure of sunlight will remove very thin reflective films from orbit like a leaf-blower moving leaves—these things are great solar sails by definition, and they tend to sail away! At the same time, anything heavy enough to stay “put” under such conditions, is too heavy to lift to orbit in the first place.

    As far as the cost of moving reflectors onto land, the same goes for mineralized paint—it’s just as heavy as mineralized plastic, and you can’t transport it by balloon. Rather, it takes very heavy equipment to move it over land, and it is difficult to evenly apply.

    Even the aerosols suggested for geoengineering, like droplets of sulfuric acid, don’t save much in mass; there is no magic to reflecting light, and it takes a minimum mass to do it. Our hypothetical 2 mm plastic sheet with area 20 million km^2 at 4 tons per km^2 has a total mass of 4 x 40 million = 160 megatons. These masses are not so different from aerosol suggestions, which are in the 10’s of megatons per year. The advantage of aerosols is that you can use wind currents to get them into place, rather like use of balloons. However, unlike the case of landed balloons, the same winds continue to move aerosols around, and they must not only be replaced, but their distribution is hard to control. Fixed reflectors on land probably beat any kind of aerosol, if balloon placement is used.

    Steven B. Harris
    July 19, 2010

  • nick


    I am so sick of hearing about geo-engineering. All it sounds like to me is a scheme to dump otherwise useless industrial waste into our atmosphere to enrich the wealthy corporations making them.

    Also, seriously, “Hack the Planet” ? That was dumb when it was in the movie “Hackers” and even worse when it’s applied to a pseudoscience we’re supposed to take seriously and hail as our savior from global climate change events.

    Life has existed on earth for a couple billion years without us here to shepherd things along. Humanity in its current form has existed a few tens of thousands of years. The planet, and life, will be fine. We may not be, but our problems are societal and will only be fixed by societal changes, not any geo-engineering magic bullets.

    You can attempt to cool the planet with these schemes, but we keep pumping out pollutants on unimaginable scales. Producing more materials to try to engineer ourselves out of this problem will just make it worse.

    Think about this, we’ve been using insecticides for a few decades now. What has that accomplished? We raise insecticide resistant insects.

  • rabidmob

    I liked the idea of spraying water into the air (instead of aerosols) as a cooling method.

    I feel that Geoengineering is going to happen (is already happening in a negative way?).

    I think though some of the issue with global warming may subside if we’re able to create massive amounts of photovoltaic power sources that also utilize infrared radiation.

  • Brian Too

    The problem with geoengineering has always been political, not technical. If you ask me anyway. The technology can be made, it can be funded, it can be deployed.

    However what happens when someone dies and the family decides that death was caused by geoengineering? Then they sue? What if the family’s house washes away and they decide that more, or better, geoengineering would have prevented that loss?

    What I can’t decide is if the difficulty of linking geoengineering activities to human outcomes will completely undermine such lawsuits. Or, conversely, will they simply encourage them?

    Either way, the best thing will probably be to avoid geoengineering entirely. It avoids the whole question of responsibility for the geoengineering outcomes. As the article states, the best we can do with geoengineering is average the outcomes. That likely means there will be some losers even when the average result is positive.


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