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Becoming Stewards of Our World: The Great Theme of the 21st Century, Part Two, Editing the Sun: A Way Out Way Out

Written by Gregory Benford

Our biosphere doesn’t respond on the time scales of our institutions. Climate change makes this clear. We’ve been running up the greenhouse content of our air for two centuries, and now the long, slow inertia of the planet has begun to respond. It’s just getting started.

Averaged over a year, the CO₂ content of our air will not be this low again for centuries—maybe many of them. The atmosphere doesn’t care about our human agendas, moral arguments or desires. It answers only to the heat balance equation.

Humanity has never confronted a problem of this kind or magnitude before. That’s part of why governments are stalling and dithering. Nobody wants to cut deeply into the meat and bone of the economy. Cutting back on fossil fuels right away is political suicide, replacing it with renewable sources within a generation is just plain impossible, and gestures at the margin distract.

We cannot know how long it will take us to respond to the two major threats we can now see:

· increasing climate change, driven at a high rate by global warming.

· the rise in acid levels in our ocean from absorbed CO₂, already well documented

There certainly will be further threats, as our numbers and influences grow. But at this early stage, in an era that will probably last centuries, we cannot know them all. We do not understand our world well enough. But we cannot simply delay.

Further, we should accept the possibility that warming alone could trigger a climactic tripping point, such as interruption of the Gulf Stream in the Atlantic. To avoid this, current thinking urges an all-out effort to shrink the human atmospheric-carbon footprint. Fine, but that leaves all the CO₂ still in the air, with more to come. Our fossil fuel burning is accelerating, not declining.

So we should also consider relatively low tech, low expense experiments, to do two things:

· accelerate our understanding of climate science, by perturbing the system and seeing how it responds—a standard experimental technique, and

· cool regions of the world, working toward restoring the climate we prefer.

This means changing the climate on purpose instead of by mistake, as we are doing now. Smart changes could return us to our earlier, milder world.

But how to do this—soon?

Reflecting on Reflectivity

What could be more intuitively appealing than simply reflecting more sunlight back into space, before it can be emitted in heat radiation and then absorbed by CO₂?

We know this every summer; black T-shirts are warmer in the sun than white ones. We already know that simply by painting buildings white they stay cooler. We could compensate for the effect of all greenhouse gas emission since the Industrial Revolution by reflecting less than one percent more of the sunlight.

Astronomers call a planet's net reflectivity the albedo, and a mere one percent decrease in Earth's albedo would solve the greenhouse problem completely for many decades. The big problem is the oceans, which comprise about 70% of our surface area and absorb more because they are darker than land.

The most environmentally benign proposal for doing this is very high tech: an orbiting white screen, about two thousand kilometers on a side. Even broken up into small pieces, putting such parasols up would cost about a trillion dollars, a bit steep. As well, we would have to pay considerably to take them down if they caused some undesirable side effect. This idea is decades old, and Roger Angel of University of Arizona advances a newer version, featuring many small panels of a few meters size.

Using more innocuous space dust to reflect sunlight does not work; it drifts away, driven off by the sun's light pressure. These ideas were no doubt amusing for the National Academy panel to toy with (even scientists need distraction), but their comic aspect detracts from the point. We do not need to go into space to fix the thermostat.

Still, attention first turned to reflectors at high altitudes because much sunlight gets absorbed in the atmosphere on its way to us. Spreading dust in the stratosphere appears workable because at those heights tiny particles stay aloft for several years. This is why volcanoes spewing dust affect weather strongly. They show that the basic idea works.

Even better than dust are microscopic droplets of sulfuric acid, which reflect light well. Sulfate aerosols can also raise the number of droplets that make clouds condense, further increasing overall reflectivity. This could then be a local cooling, easier to monitor than CO₂'s global warming. Such small, controllable experiments we could perform now.

The amount of droplets or dust needed is at most ten times smaller than the amount already blown into the atmosphere by natural processes, so we would not be venturing big dislocations. And we would get some spectacular sunsets in the bargain.

The cheapest way of delivering dust to the stratosphere is to shoot it up, not fly it. Big naval guns fired straight up can put a one-ton shell 20 kilometers high, where it would explode and spread the dust. This costs only a hundredth of the space parasol idea. Rockets, balloons and aircraft all perform worse.

But why stick to dust when we already add a perfectly good reflecting medium to the upper atmosphere as part of everyday flying—aircraft exhausts. Changing the fuel mixture in a jet engine to burn rich can leave a ribbon of fog behind for up to three months, though as it spreads it becomes invisible to the eye.

Since fuel costs about fifteen percent of airlines' cash operating expenses, for a few ten millions of dollars this method could offset the 1990 U.S. greenhouse emissions, the Kyoto Accord standard—quite a cheap choice. Even hiring air freight companies to carry dust and dump it high up would cost only ten times as much as this, so the approaches are economically interchangeable. Perhaps an added asset is that quietly running rich on airline fuel will attract little notice and is hard to muster a media-saturated demonstration against.

But there are, as always, side effects. Dust or sulfuric acid might heat the stratosphere, too, with unknown impact. Some suspect that the ozone layer could be affected, though many doubt this. If a widespread experiment shows this hazard, we could turn off the effect within roughly a year as the dust settles down and gets rained out.

Stranger ideas have been advanced. For example, making a very high altitude screen of many aluminized, hydrogen-filled balloons far above air traffic could work, and self-distribute itself over the entire globe. But the balloon parasols would cost twenty times the jet-plume approach. Ruptured balloons falling in the back garden could irritate all humanity. Imagine late-night comedians using them as props . . .

Cloudy Issues

These ideas envision doing what natural clouds do already, and the occasional volcano, as the major players in the total albedo picture. Just a four percent increase in stratocumulus over the oceans would offset global CO₂ emission. Land reflects sunlight much better than the wine-dark seas, so putting clouds far out from land, and preferably in the tropics, gets the greatest leverage.

Still, the most recent research shows that global averages are misleading, because climate dynamics depends on how spatially patchy reflectivity is. Even as we plan, we must keep in mind our ignorance of the complexities.

Making clouds is an old but still controversial craft. Clouds condense around microscopic nuclei, often the kind of sulfuric acid droplets some “geoengineers” (I prefer the term “climate restorers”) want to spread in the stratosphere. The oceans make such droplets as sea algae decays, and the natural production rate sets the limit on how many clouds form over the seas. Clouds cover about thirty-one percent of our globe already, so a four percent increase is not going to noticeably ruin anybody's day.

Tinkering with such a mammoth natural process seems daunting, but in fact about five hundred medium-sized coal-fired power plants give off enough sulfur in a year to do the job for the whole Earth. (This in itself suggests just how much we are already perturbing the planet.)

The trouble is that coal plants sit on land and the clouds must be at sea. A savvy international strategy leaps to mind: Subsidize electricity-dependent industry on isolated Pacific islands and ship them the messiest sulfur-rich coal. Their plumes would stretch far downwind and the manufactured goods could revitalize the tropical ocean states, paying them for being global good neighbors.

A more boring approach, worked out by a National Academy Panel in 1992, envisions a fleet of coal-burning ships which heap sulfur directly into the furnaces. They spew great ribbons of sulfur vapor far out at sea, where nobody can complain, and cloud corridors form obediently behind.

Best would be to use these sulfur clouds to augment at the edges of existing overcast regions, swelling them and increasing the lifetime of the natural clouds. The continuously burning sulfur freighters would follow weather patterns, guided by weather satellite data. But sulfur has bad chemical side effects. There are better things to spread—ground limestone, or diatomaceous earth. These are cheap, easy to handle, and not acidic.

At first these should operate as regional experiments, to work out a good model of how the ocean-cloud system responds. Moving from science to true stewardship of our world will take many decades. This low-tech method would cost about two billion dollars per year, including amortizing the ships.

There are other, more recent and I think better, proposed ideas for cooling by reflecting sunlight. One uses clouds formed only a few kilometers above the sea, as happens when freighters burning coal leave plumes behind. Figure. 1 shows some of these seen by satellite. The concrete proposal from John Latham and Stephen Salter, of the U.K., envisions ships that collide streams of seawater, making droplets of the right size (about a micron). These plumes shoot up for a kilometer or so and stimulate cloud production, the droplet size tuned to be brightly reflect sunlight, cooling the oceans. Figure 2 shows the ships in action. The costs seem tiny, perhaps $100 million a year, to offset present warming.

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The biggest political risk here lies with shifts in the weather. The entire campaign would increase the sulfur droplet content in our air by about a quarter. Probably this would cause no significant trouble, with most of the sulfur raining out into the oceans, which have enormous buffering capacity. Keeping the freighters a week's sailing distance from land would probably save us from scare headlines about sudden acid rains on farmer's heads, since about thirty percent of the sulfur should rain out each day.

Maybe some collaboration would work here. Freighters burning sulfur could also spread iron dust, combining the approaches, with some economies. Further scrutiny will probably turn up further savings; these calculations are back-of-the-envelope.

As well, the freighters would operate far from people's everyday lives, avoiding Not In My Back Yard movements. This is definitely not so for, say, firing dust into the stratosphere, with the booming of naval guns.

Albedo Chic

The National Academy panel found that ". . . one of the surprises of this analysis is the relatively low cost" of implementing some significant measures. Even if their rough estimates are wrong by a factor of ten, they are striking. It might take only a few billion dollars to mitigate the U.S. emission of CO₂. Compared with stopping people in China from burning coal, even hundreds of billions are nothing.

We should not hold the 1992 Panel report, thick with footnotes and layers of qualifiers, to be a road map to a blissful future. Their estimates are simple, linear and made with poorly known parameters. They also ignore many secondary effects.

For example, forests promote clouds above them, since the water vapor they exhale condenses quickly. Growing trees to sop up CO₂ then also increases albedo, a positive feedback bonus. Is this the end of the chain? Unlikely.

Perhaps the greatest unknown is social: how will the politically aware public (those who vote, anyway) react?

If they are painted early and often as Doctor Strangeloves of the air, the stewards will fail. In Fall 2006 Rolling Stone titled its story on this idea, and particularly on my collaborator, Lowell Wood, as “Dr. Evil Saves the World,” but the piece was actually pretty even-handed. On the other hand, properly portrayed as allies of science, the small band working on these ideas could become heroes.

Here a crucial factor is whether the agenda looks like another top-down contrivance, orders from the elite. A Draconian policing of illegal fuel burning will indeed look this way, but mitigation does not have to. It will play out far from people's lives, out at sea or high in the air.

Better, perhaps widespread acceptance of mitigation strategies could lead to an albedo chic, with ostentatious flaunting of white roofs, cars, the return of the ice-cream suit in fashion circles. White could be appropriate after Labor Day again.

More seriously, simply adding sand or glass to ordinary asphalt ("glassphalt") doubles its albedo. This is one mitigation measure everyone could see—a clean, passive way to Do Something. Cooler roads lessen tire erosion, too.

The urban heat island effect, which drives up air conditioning energy consumption in summer, would ease. A 1997 study by the Department of Energy showed that Los Angeles is 5 degrees Fahrenheit warmer than surrounding areas, mostly due to its dark roofs and asphalt. Cars and power plants add a bit, but not much; at high noon, the sun delivers to each square mile the power equivalent of a billion-watt electrical plant.

White roofs, light-colored concrete and about $10 billion in new shade trees could cool the city to below the countryside, cutting air conditioning costs by 18 percent and quickly paying for itself.

About one percent of the US is covered by human constructions, mostly paving, suggesting that we may already control enough of the land to get at the job. Many small measures could add to a global change. Every little bit would indeed help. This is crucial: mitigation wears the white hat. It asks simple, clear measures of everyone, before going to larger scale interventions. Grass-roots involvement should be integral from the very beginning.

This should go apace with efforts at the nation-state level, especially since mitigation intertwines deeply with diplomacy. Here appearances are even more critical, given the levels of animosity between the profligate burners (especially the U.S.) and the tropical world.

Plausible solutions should stay within the National Academy of Science Panel's sober guidelines. Learning more is the crucial first step, of course. This is not just the usual academic call for more funded research; nobody wants to try global experiments on a wing and a prayer.

Active Measures

Beyond more studies and reports, we must begin thinking of controlled experiments. Climate scientists have so far studied passively, much like astronomers. They have a bias toward this mode, especially since the discernible changes we have made in our climate have been generally pernicious. Such mental sets ebb slowly. The reek of hubris also restrains many.

Most important, perturbations in climate must be local and reversible—and not merely to quiet environmentalist fears. Only controlled experiments, well diagnosed, will be convincing to both sides in this debate.

Careful climate modeling must closely parallel every experiment. Few doubt that our climate stands in a class by itself in terms of complexity. Though much is made of how wondrous our minds are, perhaps the most complex entity known is our biosphere that we take so much for granted. Absent a remotely useful theory of complexity in systems, we must proceed cautiously.

While computer studies are notorious for revealing mostly what was sought, confirming the prejudices of their programmers, methods are improving quickly. They can explore the many side avenues of weakly perturbing experiments. Invoking computer models as crucial watchdogs in every experiment will calm fears, at least among the elite who read beyond the headlines.

We can expect to see many technical tricks for offsetting climate change. The problem is broad and many angles of attack will emerge. For example, a principal source of atmospheric methane is bovine flatulence. An additive to their fodder might side-step the portion of the digestive cycle that converts about ten percent of the calories into methane, both lowering food costs and eliminating the methane.

Such interventions into our business-as-usual world could be minor in effort, but potentially large in effect. Stewardship need not be obnoxious, or even obvious. Once society accepts the principle of mitigation, ingenuity can come into play.

Still, going from the local to the global is fraught with uncertainty, certain to inspire much anxiety. We will always be uncertain stewards of the Earth. And probably the greenhouse shall not be our last problem, either. We are doing many things to our environment, with our numbers expected to reach ten billion by 2050. What new threats will emerge?

Fresh disasters shall probably spring from the many synergistic effects that we must trace through the geophysical labyrinth. Once we become caretakers, we cannot stop. The large tasks confronting humanity, especially the uplifting of the majority to