MIT Tech Review: The Geoengineering Gambit + Video of Ron Prinn
Dan Whaley
http://www.technologyreview.com/video/?vid=502
Ronald Prinn, a professor of atmospheric science and the director of
the center for global change science at MIT, says why climate
scientists have started to change their minds about geoengineering.
http://www.technologyreview.com/energy/24157/
January/February 2010
The Geoengineering Gambit
For years, radical thinkers have proposed risky technologies that they
say could rapidly cool the earth and offset global warming. Now a
growing number of mainstream climate scientists say we may have to
consider extreme action despite the dangers.
By Kevin Bullis
Rivers fed by melting snow and glaciers supply water to over one-sixth
of the world's population--well over a billion people. But these
sources of water are quickly disappearing: the Himalayan glaciers that
feed rivers in India, China, and other Asian countries could be gone
in 25 years. Such effects of climate change no longer surprise
scientists. But the speed at which they're happening does. "The earth
appears to be changing faster than the climate models predicted," says
Daniel Schrag, a professor of earth and planetary sciences at Harvard
University, who advises President Obama on climate issues.
Atmospheric levels of carbon dioxide have already climbed to 385 parts
per million, well over the 350 parts per million that many scientists
say is the upper limit for a relatively stable climate. And despite
government-led efforts to limit carbon emissions in many countries,
annual emissions from fossil-fuel combustion are going up, not down:
over the last two decades, they have increased 41 percent. In the last
10 years, the concentration of carbon dioxide in the atmosphere has
increased by nearly two parts per million every year. At this rate,
they'll be twice preindustrial levels by the end of the century.
Meanwhile, researchers are growing convinced that the climate might be
more sensitive to greenhouse gases at this level than once thought.
"The likelihood that we're going to avoid serious damage seems quite
low," says Schrag. "The best we're going to do is probably not going
to be good enough."
This shocking realization has caused many influential scientists,
including Obama advisors like Schrag, to fundamentally change their
thinking about how to respond to climate change. They have begun
calling for the government to start funding research into
geoengineering--large-scale schemes for rapidly cooling the earth.
Strategies for geoengineering vary widely, from launching trillions of
sun shields into space to triggering vast algae blooms in oceans. The
one that has gained the most attention in recent years involves
injecting millions of tons of sulfur dioxide high into the atmosphere
to form microscopic particles that would shade the planet. Many
geoengineering proposals date back decades, but until just a few years
ago, most climate scientists considered them something between high-
tech hubris and science fiction. Indeed, the subject was "forbidden
territory," says Ronald Prinn, a professor of atmospheric sciences at
MIT. Not only is it unclear how such engineering feats would be
accomplished and whether they would, in fact, moderate the climate,
but most scientists worry that they could have disastrous unintended
consequences. What's more, relying on geoengineering to cool the
earth, rather than cutting greenhouse-gas emissions, would commit
future generations to maintaining these schemes indefinitely. For
these reasons, mere discussion of geoengineering was considered a
dangerous distraction for policy makersconsidering how to deal with
global warming. Prinn says that until a few years ago, he thought its
advocates were "off the deep end."
It's not just a fringe idea anymore. The United Kingdom's Royal
Society issued a report on geoengineering in September that outlined
the research and policy challenges ahead. The National Academies in
the United States are working on a similar study. And John Holdren,
the director of the White House Office of Science and Technology
Policy, broached the idea soon after he was appointed. "Climate change
is happening faster than anyone previously predicted," he said during
one talk. "If we get sufficiently desperate, we may try to engage in
geoengineering to try to create cooling effects." To prepare
ourselves, he said, we need to understand the possibilities and the
possible side effects. Even the U.S. Congress has now taken an
interest, holding its first hearings on geoengineering in November.
Geoengineering might be "a terrible idea," but it might be better than
doing nothing, says Schrag. Unlike many past advocates, he doesn't
think it's an alternative to reducing greenhouse-gas emissions. "It's
not a techno-fix. It's not a Band-Aid. It's a tourniquet," he says.
"There are potential side effects, yes. But it may be better than the
alternative, which is bleeding to death."
Sunday Storms
The idea of geoengineering has a long history. In the 1830s, James
Espy, the first federally funded meteorologist in the United States,
wanted to burn large swaths of Appalachian forest every Sunday
afternoon, supposing that heat from the fires would induce regular
rainstorms. More than a century later, meteorologists and physicists
in the United States and the Soviet Union separately considered a
range of schemes for changing the climate, often with the goal of
warming up northern latitudes to extend growing seasons and clear
shipping lanes through the Arctic.
In 1974 a Soviet scientist, Mikhail Budyko, first suggested what is
today probably the leading plan for cooling down the earth: injecting
gases into the upper reaches of the atmosphere, where
they would form microscopic particles to block sunlight. The idea is
based on a natural phenomenon. Every few decades a volcano erupts so
violently that it sends several millions of tons of sulfur--in the
form of sulfur dioxide--more than 10 kilometers into the upper reaches
of the atmosphere, a region called the stratosphere. The resulting
sulfate particles spread out quickly and stay suspended for years.
They reflect and diffuse sunlight, creating a haze that whitens blue
skies and causes dramatic sunsets. By decreasing the amount of
sunlight that reaches the surface, the haze also lowers its
temperature. This is what happened after the 1991 eruption of Mount
Pinatubo in the Philippines, which released about 15 million tons of
sulfur dioxide into the stratosphere. Over the next 15 months, average
temperatures dropped by half a degree Celsius. (Within a few years,
the sulfates settled out of the stratosphere, and the cooling effect
was gone.)
Scientists estimate that compensating for the increase in carbon
dioxide levels expected over this century would require pumping
between one million and five million tons of sulfur into the
stratosphere every year. Diverse strategies for getting all that
sulfur up there have been proposed. Billionaire investor Nathan
Myhrvold, the former chief technology officer at Microsoft and the
founder and CEO of Intellectual Ventures, based in Bellevue, WA, has
thought of several, one of which takes advantage of the fact that coal-
fired power plants already emit vast amounts of sulfur dioxide. These
emissions stay close to the ground, and rain washes them out of the
atmosphere within a couple of weeks. But if the pollution could reach
the stratosphere, it would circulate for years, vastly multiplying its
impact in reflecting sunlight. To get the sulfur into the
stratosphere, Myhrvold suggests, why not use a "flexible, inflatable
hot-air-balloon smokestack" 25 kilometers tall? The emissions from
just two coal-fired plants might solve the problem, he says. He
estimates that his solution would cost less than $100 million a year,
including the cost of replacing balloons damaged by storms.
Not surprisingly, climate scientists are not ready to sign off on such
a scheme. Some problems are obvious. No one has ever tried to build a
25-kilometer smokestack, for one thing. Moreover, scientists don't
understand atmospheric chemistry well enough to be sure what would
happen; far from alleviating climate change, shooting tons of sulfates
into the stratosphere could have disastrous consequences. The
chemistry is too complex for us to be certain, and climate models
aren't powerful enough to tell the whole story.
"We know Pinatubo cooled the earth, but that's not the question,"
Schrag says. "Average temperature is not the only issue." You've also
got to account for regional variations in temperature and effects on
precipitation, he explains--the very things that climate models are
notoriously bad at accounting for. Prinn concurs: "If we lower levels
of sunlight, we are unsure of the exact response of the climate system
to doing that, for the same reason that we don't know exactly how the
climate will respond to a particular level of greenhouse gases." He
adds, "That's the big issue. How can you engineer a system you don't
fully understand?"
The actual effects of Mount Pinatubo were, in fact, complex. Climate
models at the time predicted that by decreasing the amount of sunlight
hitting the surface of the earth, the haze of sulfates produced in
such an eruption would reduce evaporation, which in turn would lower
the amount of precipitation worldwide. Rainfall did decrease--but by
much more than scientists had expected. "The year following Mount
Pinatubo had by far the lowest amount of rainfall on record," says
Kevin Trenberth, a senior scientist at the National Center for
Atmospheric Research in Boulder, CO. "In fact, it was 50 percent lower
than the previous low of any year." The effects, however, weren't
uniform; in some places, precipitation actually increased. A human-
engineered sulfate haze could have similarly unpredictable results,
scientists warn.
Even in a best-case scenario, where side effects are small and
manageable, cooling the planet by deflecting sunlight would not reduce
the carbon dioxide in the atmosphere, and elevated levels of that gas
have consequences beyond raising the temperature. One is that the
ocean absorbs more carbon dioxide and becomes more acidic as a result.
That harms shellfish and some forms of plankton, a key source of food
for fish and whales. The fishing industry could be devastated. What's
more, carbon dioxide levels will continue to rise if we don't address
them directly, so any sunlight-reducing technology would have to be
continually ratcheted up to compensate for their warming effects.
And if the geoengineering had to stop--say, for environmental or
economic reasons--the higher levels of greenhouse gases would cause an
abrupt warm-up. "Even if the geoengineering worked perfectly," says
Raymond Pierrehumbert, a professor of geophysical sciences at the
University of Chicago, "you're still in the situation where the whole
planet is just one global war or depression away from being hit with
maybe a hundred years' worth of global warming in under a decade,
which is certainly catastrophic. Geoengineering, if it were carried
out, would put the earth in an extremely precarious state."
Smarter Sulfates
Figuring out the consequences of various geoengineering plans and
developing strategies to make them safer and more effective will take
years, or even decades, of research. "For every dollar we spend
figuring out how to actually do geoengineering," says Schrag, "we need
to be spending 10 dollars learning what the impacts will be."
To begin with, scientists aren't even sure that sulfates delivered
over the course of decades, rather than in one short volcanic blast,
will work to cool the planet down. One key question is how microscopic
particles interact in the stratosphere. It's possible that sulfate
particles added repeatedly to the same area over time would clump
together. If that happened, the particles could start to interact with
longer-wave radiation than just the wavelengths of electromagnetic
energy in visible light. This would trap some of the heat that
naturally escapes into space, causing a net heating effect rather than
a cooling effect. Or the larger particles could fall out of the sky
before they had a chance to deflect the sun's heat. To study such
phenomena, David Keith, the director of the Energy and Environmental
Systems Group at the University of Calgary, envisions experiments in
which a plane would spray a gas at low vapor pressure over an area of
100 square kilometers. The gas would condense into particles in the
stratosphere, and the plane would fly back through the particle cloud
totake measurements. Systematically altering the size of the
particles, the quantity of particles in a given area, the timing of
their release, and other variables could reveal key details about
their microscale interactions.
Yet even if the behavior of sulfate particles can be understood and
managed, it's far from clear
how injecting them into the stratosphere would affect vast, complex
climate systems. So far, most models have been crude; only recently,
for example, did they start taking into account the movement of ice
and ocean currents. Sulfates would cool the planet during the day, but
they'd make no difference when the sun isn't shining. As a result,
nights would probably be warmer relative to days, but scientists have
done little to model this effect and study how it could affect
ecosystems. "Similarly, you could affect the seasons," Schrag says:
the sulfates would lower temperatures less during the winter (when
there's less daylight) and more during the summer. And scientists have
done little to understand how stratospheric circulation patterns would
change with the addition of sulfates, or precisely how any of these
things could affect where and when we might experience droughts,
floods, and other disasters.
If scientists could learn more about the effects of sulfates in the
stratosphere, it could raise the intriguing possibility of "smart"
geoengineering, Schrag says. Volcanic eruptions are crude tools,
releasing a lot of sulfur in the course of a few days,
and all from one location. But geoengineers could choose exactly where
to send sulfates into the stratosphere, as well as when and how fast.
"So far we're thinking about a very simplistic thing," Schrag says.
"We're talking about injecting stuff in the stratosphere in a uniform
way." The effects that have been predicted so far, however, aren't
evenly distributed. Changes in evaporation, for example, could be
devastating if they caused droughts on land, but if less rain falls
over the ocean, it's not such a big deal. By taking advantage of
stratospheric circulation patterns and seasonal variations in weather,
it might be possible to limit the most damaging consequences. "You can
pulse injections," he says. "You could build smart systems that might
cancel out some of those negative effects."
Rather than intentionally polluting the stratosphere, a different and
potentially less risky approach to geoengineering is to pull carbon
dioxide out of the air. But the necessary technology would be
challenging to develop and put in place on large scale.
In his 10th-floor lab in the Manhattan neighborhood of Morningside
Heights, Klaus Lackner, a professor of geophysics in the Department of
Earth and Environmental Engineering at Columbia University, is
experimenting with a material that chemically binds to carbon dioxide
in the air and then, when doused in water, releases the gas in a
concentrated form that can easily be captured. The work is at an early
stage. Lackner's carbon-capture devices look like misshapen test-tube
brushes; they have to be hand dipped in water, and it's hard to
quickly seal them into the improvised chamber used to measure the
carbon dioxide they release. But he envisions automated systems--
millions of them, each the size of a small cabin--scattered over the
countryside near geologic reservoirs that could store the gases they
capture. A system based on this material, he calculates, could remove
carbon dioxide from the air a thousand times as fast as trees do now.
Others at Columbia are working on ways to exploit the fact that
peridotite rock reacts with carbon dioxide to form magnesium carbonate
and other minerals, removing the greenhouse gas from the atmosphere.
The researchers hope to speed up these natural reactions.
It's far from clear that these ideas for capturing carbon will be
practical. Some may even require so much energy that they create a net
increase in carbon dioxide. "But even if it takes us a hundred years
to learn how to do it," Pierrehumbert says, "it's still useful,
because CO2 naturally takes a thousand years to get out of the
atmosphere."
The Seeds of War
Several existing geoengineering schemes, though, could be attempted
relatively cheaply and easily. And even if no one knows whether they
would be safe or effective, that doesn't mean they won't be tried.
David Victor, the director of the Laboratory on International Law and
Regulation at the
University of California, San Diego, sees two scenarios in which it
might happen. First, "the desperate Hail Mary pass": "A country quite
vulnerable to changing climate is desperate to alter outcomes and sees
that efforts to cut emissions are not bearing fruit. Crude
geoengineering schemes could be very inexpensive, and thus this option
might even be available to a Trinidad or Bangladesh--the former rich
in gas exports and quite vulnerable, and the latter poor but large
enough that it might do something seen as essential for survival." And
second, "the Soviet-style arrogant engineering scenario": "A country
run by engineers and not overly exposed to public opinion or to
dissenting voices undertakes geoengineering as a national mission--
much like massive building of poorly designed nuclear reactors, river
diversion projects, resettlement of populations, and other national
missions that are hard to pursue when the public is informed,
responsive, and in power." In either case, a single country acting
alone could influence the climate of the entire world.
How would the world react? In extreme cases, Victor says, it could
lead to war. Some countries
might object to cooling the earth, especially if higher temperatures
have brought them advantages such as longer growing seasons and milder
winters. And if geoengineering decreases rainfall, countries that have
experienced droughts due to global warming could suffer even more.
No current international laws or agreements would clearly prevent a
country from unilaterally starting a geoengineering project. And too
little is known now for a governing body such as the United Nations to
establish sound regulations--regulations that might in any case be
ignored by a country set on trying to save itself from a climate
disaster. Victor says the best hope is for leading scientists around
the world to collaborate on establishing as clearly as possible what
dangers could be involved in geoengineering and how, if at all, it
might be used. Through open international research, he says, we can
"increase the odds--not to 100 percent--that responsible norms would
emerge."
Ready or Not
In 2006, Paul Crutzen, the Dutch scientist who won the Nobel Prize in
chemistry for his discoveries about the depletion of the stratospheric
ozone layer, wrote an essay in the journal Climatic Change in which he
declared that efforts to reduce greenhouse-gas emissions "have been
grossly unsuccessful." He called for increased research into the
"feasibility and environmental consequences of climate engineering,"
even though he acknowledged that injecting sulfates into the
stratosphere could damage the ozone layer and cause large,
unpredictable side effects. Despite these dangers, he said, climatic
engineering could ultimately be "the only option available to rapidly
reduce temperature rises."
At the time, Crutzen's essay was controversial, and many scientists
called it irresponsible. But since then it has served to bring
geoengineering into the open, says David Keith, who started studying
the subject in 1989. After a scientist of Crutzen's credentials, who
understood the stratosphere as well as anyone, came out in favor of
studying sulfate injection as a way to cool the earth, many other
scientists were willing to start talking about it.
Among the most recent converts is David Battisti, a professor of
atmospheric sciences at the University of Washington. One problem in
particular worries him. Studies of heat waves show that crop yields
drop off sharply when temperatures rise 3 °C to 4 °C above normal--the
temperatures that MIT's Prinn predicts we might reach even with strict
emissions controls. Speaking at ageoengineering symposium at MIT this
fall, Battisti said, "By the end of the century, just due to
temperature alone, we're looking at a 30 to 40 percent reduction in
[crop] yields, while in the next 50 years demand for food is expected
to more than double."
Battisti is well aware of the uncertainties that surround
geoengineering. According to research he's conducted recently, the
first computer models that tried to show how shading the earth would
affect climate were off by 2 °C to 3 °C in predictions of regional
temperature change and by as much as 40 percent in predictions of
regional rainfall. But with a billion people already malnourished, and
billions more who could go hungry if global warming disrupts
agriculture, Battisti has reluctantly conceded that we may need to
consider "a climate-engineering patch." Better data and better models
will help clarify the effects of geoengineering. "Give us 30 or 40
years and we'll be there," he said at the MIT symposium. "But in 30 to
40 years, at the level we're increasing CO2, we're going to need this,
whether we're ready or not."
Kevin Bullis is Technology Review's Energy Editor.
Copyright Technology Review 2009.