Gardening the atmosphere

kw: book reviews, nonfiction, global warming, geoengineering

A new book about global warming, pro or con, seems to come out every week. I've come to avoid them. One can only endure so many polemics. How to Cool the Planet: Geoengineering and the Audacious Quest to Fix Earth's Climate by Jeff Goodell is a middle-ground book. He takes human-caused global warming as a premise, and asks, "What can we do about it?"

It turns out there are just three approaches that could make a substantial difference:

1. Reduce carbon dioxide emissions
2. Shield the earth with a reflecting layer (AKA geoengineering)
   
3. Extract carbon dioxide from the atmosphere and store it somewhere (sometimes AKA geoengineering)
   

It has proven politically impossible to get anywhere with #1. #3 appears to be extremely costly. Now #2, well, it is cheap, but only in a monetary sense. It has so far proven too politically costly for anyone with the temerity to try an experiment. Also, the "mitigating" approaches, #2 and #3, are seen by many as a way for "big oil" to claim we don't need to do anything about carbon emissions: "just balance the emissions with sufficient geoengineering efforts and everything will be all right." Of course, "big oil" also claims carbon emissions aren't doing any harm in the first place.

Then we need to ask the question, whose ox is being gored here? What of people who think global warming (should it be happening) is a good thing? After all, other than the lack of air conditioning, and a little political bad news called feudalism, things were pretty good during the Medieval Climate Optimum a thousand years ago, when global temperatures were about two degrees C warmer than they are right now. (Personally, I prefer a slightly cooler climate. I am living about as far south as I can tolerate already. Maybe it is time to buy land in Canada!)

The author is wise to set aside the "reduce carbon emissions" argument. There are books aplenty on the subject, and a realistic look at the Montreal and Copenhagen debacles shows just how unlikely it is that the U.S., China, India and Japan will enact any significant changes in their economies. And there is nearly nobody else who matters, in this arena, just the E.U., but they are a distant fifth place in emissions; were they to emit zero carbon starting tomorrow, the effect would be pretty small. So instead, we are treated to an interesting tour of the various geoengineering methods and their proponents.

Carbon sequestration has two flavors: chemical extraction and storage, and "getting the plants to do it". In his second chapter, Goodell presents the work of David Keith in Calgary. Dr. Keith is building a prototype chemical extraction device. A test run in the author's presence reduced CO₂ by one part per million, or about 1/3 percent of its abundance. Dr. Keith is optimistic that engineering improvements can increase efficiency to a level near 10ppm (3% of total abundance).

The machine uses cheap chemicals, but in large amounts. To reduce atmospheric carbon from the current level (380ppm) to a pre-industrial level (280ppm), you'd have to pass the entire atmosphere through an array of these machines, ten times. Let's think about this. The weight of the atmosphere is 14.7 pounds per square inch, or 1.03 kg/cm². We want to remove 100ppm of it, or a portion of 0.0001; 0.0235 oz/in² or 0.103 g/cm². Let's go metric from here.

The surface area of Earth is half a billion square kilometers. A km is 100,000 cm. The math produces a requirement to "capture" more than 500 trillion kg, or 500 billion metric tonnes, of carbon dioxide. Dr. Keith's machine converts the gas to limestone, CaCO₃. 56% of the limestone is calcium oxide, CaO, so the end result would be 1.2 trillion tonnes of limestone. Let's see, the stuff has a specific gravity of 2.7, so a cubic meter weighs 2.7 tonnes; the volume is about 440 billion m³ or 440 km³. Anybody need a second White Cliffs of Dover, or have a place to put one? Maybe we could re-fill old open-pit mines. This is the amount of carbon storage needed to remove 100ppm from the atmosphere, whether it is to yield a pre-industrial atmosphere, or to keep the next 100ppm from accumulating in the first place.

How 'bout getting the trees to do it? You don't have to tie up half a trillion tons of calcium oxide to get this one to work; the gas gets converted to cellulose. Cellulose, however, is light. Hardwoods have specific gravities in the range 0.6-0.85. Let's pick 0.7 as an average. Here, you are tying up water with carbon dioxide in a 1:1 ratio, but releasing oxygen, so 44 grams of CO₂ produces 30 grams of cellulose. This is a benefit; you "only" need to produce 360 billion tonnes of wood to take 100ppm out of the atmosphere. But the volume of that wood is greater than the volume of the limestone above, just over 500 km³. Anybody ready to plant about ten trillion trees?

Fertilizing the oceans has also been seen as a possible solution. Iron is the rate-limiting nutrient in many parts of the open ocean. Here, experiments have actually been done, but not with geoengineering in mind. Impressive plankton blooms, visible to satellites, have resulted. But you still have the volume problem. How many cubic km of diatoms and coccolithophorids do you have to produce for half a thousand km³ of them to fall to the ocean floor and stay there?

So we come to global shields, of two types. Half the book investigates the scientific, political, and social aspects of these. One method is cloud-brightening, the other is sulfate-aerosol-blocking. In the book the author reports that it takes not millions but billions of condensation nuclei to make a cloud whiter so it reflects more sunlight. Actually, nuclei of the right size require droplets just under a micron in diameter; there are about a quadrillion such droplets produced from each liter of sea water one sprays. A quadrillion is a million billion (in American numbering, anyway). It takes thousands of liters of spray to make a substantial effect over a few square km of area. So far, no experiment has been tried, because of huge fears by environmentalists.

So: sulfate aerosols. This is potentially the cheapest method. Pump a lot of micron-size sulfur dioxide droplets into the stratosphere, and they'll stay there for 3-5 years, reflecting extra sunlight all the while. I wonder what astronomers think of the idea? Globally, some $20 billion have been invested in large telescopes in the past twenty years. How many of them would be rendered a lot less useful by a sulfate haze? The primary selling point of this approach is that we're not moving half a thousand cubic km of stuff, just a few thousand cubic meters.

The numerical analyses above are my own, not the author's. In a few places, he calls some of these methods akin to bad science fiction. He also worries about military uses of geoengineering technologies. There doesn't seem to be a good way of dealing with global warming. Yet his is a hopeful book. Human nature being what it is, we are likely to do something heroic when we really need to. As usual, heroes are a vanishingly small minority, so when the true crunch arrives (such as the imminent flooding of NYC or Bangladesh), a few visionaries will likely drag the rest of the human race, kicking and screaming, into a new kind of global economy. Let's hope the death toll is less than half of humanity.

I am hopeful in another way. The Medieval Climate Optimum showed that significant warming did not heat the ocean enough to make it rise much, at least not during that 400-year warming event. The real danger is melting ice caps, the ones on land, which are Greenland and Antarctica. They didn't melt much a thousand years ago.

All kinds of dreary forecasts are based on positive feedback effects. Negative feedback seems to be less well known, or ignored. I expect a warmer total climate to produce more polar snowfall, perhaps building Antarctica faster than it is being melted at the edges. Will a warmer planet be a cloudier planet? That's a possible negative feedback effect. Nobody at present knows. There is not one "global climate model" that models clouds properly. Cloud dynamics are still poorly known.

However, I am in favor of experimentation. How are we to know the effects of nano-nucleation of clouds without actually nucleating some clouds? Macronucleation for rainmaking purposes didn't work too well, but maybe cloud brightening can be one useful tool. Maybe sulfate aerosols can be "spot applied" in the stratosphere, and maybe not. We don't know if it could be helpful, or even possible, without trying. Can iron fertilization of ocean water do any good, or do enough good? Can't know until we try. The prime virtue of all these is, if things go bad, you just stop. In short order, natural processes will eliminate the change.

Goodell makes a good analogy here, that we ought to consider carefully. We are already engineering the atmosphere, as a by-product of energy use. Geoengineering methods that attempt to gain more control of the global thermostat are akin to gardening. There is no question that a garden is not a natural landscape. But it is not entirely artifice either. It is a synergy of human planning and natural processes, a compromise between gardener and nature. We will probably never be able to "produce" a pleasant, sunny day on demand in any particular location, nor order up a centimeter of rain when and where it is urgently needed. But we may be able to modify overall probabilities, to "tilt the roulette wheel" a little. Maybe.

In the longest of long runs, we'll run out of carbon based fuels. We won't add any more carbon to the atmosphere because we won't have any to add. What kind of world will that be? Will we have had the foresight to develop truly renewable and sustainable energy-production methods? Or will it be a return to horse-and-buggy days? Will anyone still have air conditioning? How much CO₂ will the atmosphere hold by then? 1000ppm? Things could be a lot different.