ARE you doing your bit for the planet? You’ve stopped driving a car, planted
six trees in your back garden and put solar panels on your roof. You’re even
willing to breathe more slowly if it’ll help reduce your carbon dioxide burden
on the poor overheated planet. But the temperature continues to creep up.
There’s already too much CO2 in the air and you realise that things are
going to keep getting hotter. So what can you do?
Some researchers would like you to turn to an entirely different way of
fighting global warming. If you can’t plug the flow of carbon into the
atmosphere, they argue, then cool the planet by blocking some of the light from
the Sun. Over the past few years, they’ve come up with a host of bright ideas
for how to install a dimmer switch on daylight. Such as putting a giant mirror
in space. Or letting loose a layer of dust, a giant metal mesh or trillions of
tiny silver balloons into the atmosphere. Anything to give us a global
thermostat, to pull down the temperature when things get too hot.
If you find this prospect disconcerting, you’re not alone. Ken Caldeira, a
climate researcher from the Lawrence Livermore National Laboratory in
California, is terrified by the whole idea. So he set out two years ago armed
with a global model to try to prove that it wouldn’t work. But things didn’t
quite turn out like that. To his dismay, everything he thought would go wrong
when he ran his model, went right. His work did more to support planetary
geoengineering than to shoot it down. But he won’t be cutting down the trees in
his garden just yet. Like many other researchers he’s still disenchanted with
the whole idea. And they have plenty of reasons to be concerned.
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The idea of geoengineering the planet by regulating our daily dose of
sunlight has been around for a while. Ways to deflect sunlight range from the
bizarre—setting a styrofoam continent adrift in the Pacific—to the
mundane, such as painting all our roofs white. And in 1993, Russia successfully
diverted a few of the Sun’s rays with an orbiting mirror (see “Playing with
fire”). The appeal of such schemes lies in their potential to bail us out
of a future environmental crisis. If our climate starts to run out of control,
some argue, incremental reductions in greenhouse gas emissions won’t be nearly
enough. Instead we’ll need something that has an immediate dramatic impact. And
geoengineering could supply just that.
If we don’t change our current habits, in fifty years’ time the amount of
CO2 in the Earth’s atmosphere is expected to reach twice the
pre-industrial value. The expected warming from that doubling is predicted to be
something like 2.5 °C. To counter that, a reflective shield would only need
to block about 1.8 per cent of the Sun’s light. The further you get from the
planet, the smaller and more efficient that shield can be, but the harder it is
to put it there.
The most ambitious option, first proposed by James Early in a Lawrence
Livermore National Lab report in 1989, is a 2000-kilometre-wide solar shield in
orbit about 1.5 million kilometres from Earth. The satellite would sit in a
sweet spot known as the Lagrange point—a place where the gravitational
pulls from the Earth and the Sun, and the centripetal force of the satellite’s
orbit, all cancel each other out. Best of all, the angle of the shield could be
tweaked, making for an adjustable thermostat.
A more complicated option is a swarm of smaller reflectors buzzing around in
near-Earth orbit. Back in 1991, the National Academy of Sciences (NAS) in
Washington DC found that around 50 000 of them, at 100 square kilometres apiece,
would do the trick.
Still closer to home, you could inject small particles into near-Earth orbit
or the upper atmosphere. Sulphur dioxide, for example, is belched out by
volcanoes and already naturally cools the planet. Depending on your substance of
choice, you’d need anything from a thousand to 10 million tonnes. The NAS found
two fairly economical potential delivery systems: using battleship guns to fire
dust about 19 kilometres into the atmosphere, or fitting jet planes with adapted
exhaust pipes to fire smoke upwards as they flit through the sky at altitudes of
around 13 kilometres.
More recently, some of Caldeira’s colleagues at Livermore updated the details
to see how we could actually go about diverting the sunlight. Edward Teller, the
founder of the Livermore labs, worked with Lowell Wood and Roderick Hyde to
recalculate the details of releasing particles into a near-Earth orbit, with
modern engineering in mind. Surprisingly, they found it could cost a mere
billion dollars a year—a hundred times cheaper, they say, than the costs
associated with drastically reducing our use of fossil fuels. There are
materials, they claim, that could be used with minimal effect on the
environment, but maximum reflection of the Sun. These include small metal
plates, organic dyes, tiny helium-filled silver balloons or even
potassium-filled buckyballs. And, they add, the scheme has the added benefit of
not requiring the kind of ongoing political or social effort that a massive
reduction in fossil fuels might entail.
“Teller and Wood are technical optimists, and pessimists about human
behaviour,” says Caldeira, who saw Wood present their work in 1998, and was
disturbed by the re-emergence of these Sun-blocking proposals. “My hope was to
show that it wouldn’t work,” he says, “so people would give up on it.”
Caldeira thought he saw a central flaw in all of these Sun-dimming ideas.
While reducing sunlight might have an overall cooling effect on the planet as a
whole, he argued, it wouldn’t counteract the local heating effect from CO
2. The two forces act in a completely different way on different parts of
the globe. The capacity of CO2 to trap heat increases with temperature,
so it’s more effective near the equator. The Sun, on the other hand, shines more
in the northern hemisphere in June, more in the southern hemisphere in December.
Surely, thought Caldeira, these very different phenomena couldn’t exactly cancel
each other out? Not on a country-sized scale, or over the different seasons.
Instead, he expected the winters to get warmer and the summers cooler, the poles
warmer and the tropics cooler. In short, many of the problems the Earth faces
from global warming—the seasons becoming more and more alike, and a
variety of weird weather
(91av, 16 September, p 26)
—would be made worse.
To try to prove his hypothesis, Caldeira went to work with his colleague Bala
Govindasamy and a hefty climate-modelling program. They invented three future
worlds to test. In the first, the control model, levels of atmospheric CO2
were set at just 280 parts per million—the pre-industrial
value—and the Sun shone at a constant 1367 watts per square metre at the
Earth’s surface. In the second, there was twice as much CO2, adding an
extra 4.17 watts per square metre to the Earth-bound radiation. In the final,
geoengineered scenario, the doubled CO2 was countered by cutting 1.8
per cent of the Sun’s light, again worth 4.17 watts per square metre. The worlds
weren’t meant to be entirely realistic. Caldeira just wanted to see how these
two effects alone would play off each other.
Cold shock
After three months crunching out temperature and weather maps for the planets
with a resolution of 200 square kilometres, the worlds emerged from a 40-year
lifespan. The doubled-CO2 world turned out just as you’d expect from
other climate models. It warmed more in winter than summer at high latitudes,
because there was less sea ice to reflect the sunlight and keep the polar
regions cool. Overall, the global temperature went up by 1.75 °C, the volume
of sea ice went down, and it rained more at high latitudes as additional water
evaporated into the clouds near the equator.
But when it came to the geoengineered planet, the researchers got a shock.
This world looked very much like the control model. Only about 15 per cent of
the planet’s surface was significantly warmer or colder than the control,
compared to a whopping 97 per cent for the doubled-CO2 model. As the
results began to appear, Caldeira raised an eyebrow at the numbers. And the more
he saw, the less he understood. “Oh my God, even in the winter it’s all
cancelling out. What’s going on?” he remembers asking Govindasamy.
After some thought, they realised that sea ice was playing a crucial role in
the geoengineered world. Cooling the planet meant that more sea ice formed, and
not only did the white ice reflect more light, it also insulated the warmer
ocean water from the overlying air. That kept the winter atmosphere near the
poles nice and nippy. And somehow that was enough to cancel out global
differences between the warming from CO2 and the cooling from the
reduced sunlight.
Can the results be trusted? “I believe about 85 per cent that the local
seasonal effect will be cancelled,” says Govindasamy. Mike MacCracken, executive
director of the National Assessment Coordination Office in Washington DC and
author of several papers investigating geoengineering for the Livermore labs
some years ago, isn’t so sure. “I’m a little perplexed by their result,” he
says, since other factors like the amount of sulphur dioxide in the atmosphere
have been shown to have a local effect. Industrial pollution, created more in
the north than the south, is usually assumed to be partly responsible for a
temperature difference between the two hemispheres. “I’m not convinced this
issue is resolved yet,” he says.
Which at least leaves room for Caldeira’s wishes to come true. “It has been
suggested to us that we shouldn’t publish this,” he admits, since the results go
against their ideals. But the paper came out in Geophysical Research
Letters (vol 27, p 2141) this July. And along with it, both published and
repeatedly expounded by Caldeira and others, comes a grocery list of problems to
temper the conclusion that geoengineering might actually work.
Those include the obvious fact that the model is incomplete. The Earth is a
complex thing, with cloud patterns, ice cover, plant productivity, smog, fires,
volcanoes and more all affecting the climate. Some of these factors are so
poorly understood that no one actually knows if they have an overall cooling or
warming effect. So tinkering with something as crucial as sunlight doesn’t
really seem like a good idea—it’s just adding one more variable to an
already huge equation.
Another problem comes from an effect that this kind of geoengineering can’t
cancel out. Right now, the stratosphere is cooling as the surface temperature
creeps upwards, since the warm air that would normally rise to heat it is being trapped below
(91av, 1 May 1999, p 28). Reducing the amount of
sunlight just makes it colder. And that makes for more polar stratospheric
clouds, which provides more ice to act as a substrate for ozone-destroying chemical reactions
(91av, 25 March, p 24). “This isn’t good
for the ozone,” says Caldeira.
But aside from the science, there are other issues to consider. Caldeira and
others point out that all the proposed solutions are costly and difficult to
implement. Putting 50 000 little mirrors in near-Earth orbit would cost about
$120 billion a year to launch and maintain, according to the NAS. Once
they’re up there, you’d be hard pressed to get them down. And the challenge of
preventing them from colliding with each other as they whiz around would be
considerable. Not to mention the eclipse-like effect, says MacCracken. “You’d
have a sort of flickering Sun, which I don’t think people would care for
ܳ.”
As for particulate matter in the atmosphere, this is at least relatively
cheap at less than a billion dollars per year. And since the stuff would fall
back to Earth in a few months to 10 years, the act is not permanent. But it
would be difficult to prevent the particles from reacting chemically, destroying
ozone in particular. And, adds MacCracken, it could have the unsettling effect
of turning the sky white.
The least disruptive option is the solar shield in orbit at the Lagrange
point. That’s so far away no one would really notice it. But this option
involves an astronomical up front cost—anything from $1 to
$10 trillion—and would probably entail putting a manufacturing
plant for its construction on the Moon. Govindasamy’s guess: “That’s probably
not going to happen.”
But there’s a more fundamental problem with this whole approach, says
Caldeira. “The big concern with the satellites, aside from the ridiculous cost,
is catastrophic failure. What happens if this thing is out there and the
mechanism fails?” Then we’re left with a carbon-overloaded atmosphere and no way
to counteract the heating.
And there’s a more sensitive issue too, as anyone living in rain-soaked
Vancouver or the arid Sahara might appreciate. When we get a global thermostat,
who decides what the setting should be? “What is the optimum climate?” asks
MacCracken. “There’s no way we’d come to an international agreement on that.” In
offices, fights already break out over the air conditioning. Imagine that kind
of squabble scaled up to a global level, and the picture is frightening.
For some, geoengineering looks like the fix that will save us from destroying
our own planet. For others it’s just another way to dig a deeper grave. To the
most pessimistic, geoengineering is a runaway technology that we won’t be able
to control, with devastating side effects and catastrophic consequences if it
fails. But in the end, there’s more than one thing to be scared of. “In a sense
we’re already doing as big a change to the atmosphere by adding carbon dioxide
in the first place,” says Caldeira. “That’s kind of frightening too.”
Some scientists have dabbled in geoengineering already. In 1993, a 22-metre
plastic mirror was mounted on the side of an orbiting Russian spacecraft. Named
Banner, the umbrella-like mirror was destined to divert light from the Sun. But
not to reduce the amount reaching the Earth. The idea was to increase it.
Their plan was to provide extra daylight to Sun-starved cities in the North,
giving a boost to growing seasons and spirits across the Russian countryside.
Banner was just a test run for a larger project, but it had a noticeable effect.
A weak four-kilometre-wide beam of sunlight flashed across the continent for six
minutes one night, in a display that one observer described as “luminous
diamonds following one another across the sky”. The controversial project
eventually fell apart. But it showed that the idea of diverting the Sun’s light
could work.