originally published June 4, 2013

Global Warming — What Do We Do?

So what course should we take to confront global warming?

First of all, that we should conserve energy, reduce fossil fuel consumption, and migrate to renewable energy resources as rapidly as we can, is not open for debate. Anyone who denies the need for such effort is just irresponsible. I’m asking, what do we do beyond that? How do we handle the growing consequences of the carbon dioxide levels we’ve already created, and will continue to add to even if we make our best effort to reduce the problem?

There are three basic categories of response: try to clean up the CO2, try to reduce solar heating, or do neither. To be more specific, here are some approaches that have been suggested:

I think the last two options, despite the obvious and inarguably disruptive ecological impact they would have, might actually be the least bad, and would quite likely be better than doing nothing. There are plenty of people who feel likewise — in at least one case, strongly enough to openly defy the law to give the plan a try. Let’s get into some details to see why.

As mentioned, there are two broad categories of answers here, besides doing nothing: ones that reduce carbon dioxide, and ones that don’t reduce carbon dioxide but do reduce heat. I think we should prefer the ones that tackle the carbon dioxide itself, because it’s ecologically harmful even if the temperature doesn’t change. The reason for this is that when it dissolves into seawater, some of it ends up forming carbonic acid, lowering the pH of the whole ocean. The change is subtle, but the ecological effect may be quite substantial. Any critter that secretes a calcium shell or skeleton, from clams to coral, has a much harder time forming the necessary minerals in acid water. An acidified ocean might cause a global crash in coral reefs (which are already stressed for other reasons), leading to a loss of biodiversity comparable to the loss of the Amazon rainforest. That would be bad. Also, a variety of other marine life, such as ordinary fish, would simply be less healthy in acidified water. All in all, the ecological impact of acidification might be worse than that of the temperature increase.

On the other hand, maybe it’s possible to adapt. After all, seawater may have been more acid than today in the warmer past, when the atmosphere had higher CO2 naturally. But it’s estimated that the current rate of change is a hundred times that which life adapted to in the past. I’d rather not take the chance, and that means I think we’d better focus on tackling carbon dioxide, not on tackling heat. This leaves out the solar mirrors, stratospheric dust, cloud seeding, and white paint as global warming solutions.

Industrial processes for sequestering carbon from the air are absurdly costly — for instance, if a coal power plant were to capture its waste carbon output, the sequestration process might use half of the energy that burning the coal produces, making the whole process ridiculously uneconomical. We’d not only have to substantially increase the size and cost of the plant to add the sequestration machinery, we’d have to double both parts again to regain the lost output capacity. We might as well just switch from coal to plutonium.

I think the one realistic approach to soaking up lots of carbon dioxide is to do it biologically, with plants or plankton. These approaches divide into two groups: land-based and ocean-based. Of course, we could use both.

The thing is, the land-based approaches are all up against the need to use a lot of land which is already in demand for other purposes. Anything that makes the sequestration effort big enough may end up in direct conflict with the shorter-term needs of food production and so on. In the ocean, on the other hand, there’s no serious competition over the resource, so we could operate on as large a scale as we choose to.

On the other hand, while fertilizing the ocean to cause plankton blooms is clearly disruptive and “unnatural” for the history of that environment, it’s clear that restoration of forests, prairies, and wetlands is an inarguable good. We should certainly do as much of these as we can manage to make politically feasible. If that amount is sufficient to handle the problem, then we don’t need to mess with the ocean, but I’m pretty sure it won’t be nearly enough.

How would we carry out the fertilization? The main way that people are discussing is to spread shiploads of iron sulfate powder into the water. (This is currently illegal under laws against dumping possibly toxic waste.) This enriches the water with available iron, which as the most limited nutrient, is what currently sets the ceiling on plankton growth. This would be done mainly in the tropics, where the water is the most unfertile. (Unlike the case on land, in the ocean life is usually densest in the cold areas.) Once the plankton bloom, everything that feeds on them have a growing population as well, until eventually even the big fish are thriving. They estimate that each ton of iron used would grab several thousand tons of carbon. This trick has been tried several times on a small scale... sometimes it worked, other times the results were disappointing. Obviously there’s more to learn.

There’s also a cheaper way to do it, and that is just to circulate deep water up to the surface. In the tropics, the deep waters, where there’s no sunlight, have a good deal more nutrient value than the shallow water has. Pumping even a small amount of it to the surface can create a noticeable bloom.

There was a cheap experiment done in 2008 using a simple cloth tube with a valve at the bottom and a float at the top, where wave action would gradually suck water up to the surface. Two tubes were set afloat for a month. Both tore apart well before the month was up, one of them lasting only a day or two, and yet the area around it still showed a dramatic enrichment not just in plankton, but in large fish, which had congregated. Now recirculating deep water will obviously tend to bring some sinking carbon back up again, but anything that increases biomass will inevitably raise the rate at which residue sinks to the ocean floor, as well as greatly increasing the carbon held at any given time within active biomass. Dead diatoms, especially, tend to carry their carbon right to the bottom. I think this approach, being so simple and easy, may be more fruitful for really large scale operations than the iron sulfate approach is. Of course, adding a bit of iron might still be worthwhile for helping us get the most out of the deep water’s other nutrients; a mixed approach might be best.

Another factor is that the deep water is cold. Some say that by bringing it up, you could actually generate electricity, making the whole operation pay for itself. Plus, that helps us drain a bit of heat out of the atmosphere for the short term.

It’s also speculated that plankton fertilization would have the indirect effect of making the air a bit cloudier, which would help reflect sunlight. This is because dimethyl sulfide released by some plankton species would tend to produce sulfate particles in the air, which could have a cloud-seeding effect.

David Brin, the futurist and science fiction author, has an article here about several different methods that might be used to fertilize plankton.

Now there are some obvious criticisms that can be raised against any means of fertilizing plankton blooms in the ocean, and also some that are not so obvious. For instance, besides the unavoidable disruption to the current balance of the food chains, they say that it will raise the pH of surface water but lower the pH of deep water. (This may be true, but the shallow water is a hundred times as important. The same issue applies to oceanic sequestration from smokestacks.) They say that though some of the captured carbon sinks to the bottom and is sequestered permanently, a lot of it does not sink all the way, but will recirculate from deep water back to the atmosphere many years later. (The same is true of most land-based approaches such as encouraging forests and wetlands.)

On the other hand, some scientists argue that we’ve already somehow depleted the degree of fertilization that plankton receive from airborne dust, and boosting it back, within limits, is just restoring a previous status quo. (This is disputed.) And there’s no question that most of our ecological effects on the ocean have been to decrease overall biomass, especially of fish... and to me, even if the balance of species is not what it was, something that boosts it back up again, and encourages larger fish populations again, sounds like a plus. We’ve been trying to turn the ocean into a desert; turning it back into a jungle is surely not as bad as continuing to deplete it.

Some proposals directly address the issue of the plankton just giving up its CO2 back into the atmosphere before it sinks. The best I’ve heard so far is by William Calvin. He suggests one pump drawing deep water up (and adding some air bubbles), and downstream of it in the local current, a second pump pushing surface water back down. The water heading down would be far more carbonaceous than the water pulled up, as it would include the carbon inside still-living plankton, which would settle out once they’re pushed to depths without sunlight. And this would reduce the impact on the rest of the ocean ecosystem — the effect on fish populations and so forth would be more manageable in proportion to the amount of carbon sequestered. Both pumps could be adequately powered by waves (if each pipe is small), or wind (if fewer and larger). Large ones could be built onto old oil platforms. And the whole thing could be done in coastal waters, because these produce natural currents where the surface water moves toward shore and the deep water moves back out to sea.

Can it do enough? Apparently not. It may be the most economical way we can soak up large amounts of carbon dioxide, but it’s been estimated that the highest rate of absorbtion the oceans could support is well short of enough to keep up with the rate that new CO2 is being added to the atmosphere by industry. We’d have to do more, but it’s at least a solid start.

Land-based sequestration certainly shouldn’t be counted out... it’s recently been noticed that most of the sequestration in forests is done not by the trees, but by fungi in the soil. There are probably lots of places we can encourage fungi even on land that isn’t “set aside” in some way. Tidal marshes and mangrove swamps are an area of opportunity, as they sequester a lot more carbon than a similar area of forest, and are also beneficial for lots of marine life. We’ve lost a lot of wetlands over the centuries, and re-expanding them would just restore some balance.

But if we want to process a lot of carbon on land quickly, maybe slow-growing trees and fungi aren’t the efficient way to do it. Some years ago, before wind and solar power became economically competitive, there was talk of using “biomass” as a replacement for coal. Plant fast-growing trees, and just burn wood. It would be carbon neutral. And we’re often thinking similarly when considering sequestration: grow wood, then use it as lumber or bury it. But the biomass people found that turning sunlight and CO2 into burnable plant tissue could be done more quickly and efficiently by growing grasses than by growing trees. Simpler and smaller organisms are more effective than big elaborate ones, just as is the case with the plankton at sea.

The most effective carbon absorbers might be simple ponds of algae. Dump in sewage or manure (I imagine such ponds might often be operated in conjuction with a dairy or feedlot), let it turn green, then scrape out the muck. You’d have to tune the organisms to grab the maximum of carbon with the minimum of nitrogen, and especially of phosphorus, which we have to watch our supply of. If you get the algae to produce lots of oils or waxes, or even starches or sugars, that would take up a lot of carbon.

An interesting possibility is that some algae have an alternate photosynthesis pathway which yields hydrogen gas instead of oxygen. This would enable you to produce clean-burning fuel at the same time that it takes up carbon. It might not be the most effective carbon absorber, but the side benefit of producing hydrogen might offset that economically, making the ponds pay for themselves. Definitely worth exploring. Of course it would be difficult to build this up to the necessary scale, but that’s why we have to also do the ocean plankton at the same time.

A lot of humans like to make policy choices by a conservative principle that says that if what you’re going to do might be risky, then you should be biased toward inaction and leaving things as they are. This idea automatically makes us think that taking a risky move like this is unwise and dangerous, and it’s better to leave things alone. But the thing is, to let global warming and ocean acidification run wild is not “leaving things alone”. If the risky choice might have things go bad, but the conservative status-quo choice is certain to, then we have to adjust our conception of what the real risks are.

Here’s a metaphor for ya: we’re in a car driving toward a cliff. One passenger advocates spinning the wheel around and going into a skid and doing a fancy stunt-driving maneuver that may end badly, in an attempt to avoid the cliff. The other (the one at the wheel) thinks that this sounds awfully dangerous and imprudent, and that we should keep driving calmly and serenely, with only gentle corrections, even though this heads us straight over the edge.

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