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Overview of Climate Engineering
Eli Kintisch
Science Magazine
Massachusetts Institute of Technology
Top science institutions around the world, including the US National Acad-
emies and the UK Royal Society, have called for studies into deliberate tinkering
with the planet’s climate or atmosphere to partially offset global warming, a
practice known as climate engineering or geoengineering. Various characteristics
distinguish the two major types of geoengineering: solar radiation management
(SRM; e.g., orbiting sunshades, aerosols sprayed into the stratosphere) and carbon
dioxide removal (CDR; e.g., carbon-sucking machines, catalysis of oceanic algal
growth). The number of scientists studying both is steadily increasing, and sev-
eral companies are conducting CDR engineering research, but the United States
has yet to follow the lead of a number of European countries that have dedicated
programs for geoengineering research.
Efforts at global carbon dioxide pollution abatement remain stalled even
as the effects of a warming planet become increasingly apparent. Research
findings suggest that the planet may be closer to global tipping points, such as
the release of methane from permafrost, than previously thought. As the global
climate crisis intensifies, taboos once held by scientists and policymakers are
falling by the wayside. Adaptation, the organized response to a warming planet
and its myriad local impacts, was once viewed by top officials as a distraction
from the main priority of mitigating global greenhouse gas emissions. Now local
and national governments around the world are creating plans to respond and
adapt to warmer temperatures, higher seas, more pervasive drought, and other
environmental challenges.
Geoengineering is a radical form of adaptation. The publication in 2006 of a
controversial paper by Nobel Prize winner Paul Crutzen titled “Albedo Enhance-
ment by Stratospheric Sulfur Injections: A Contribution to Resolve a olicyP
5
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6 FRONTIERS OF ENGINEERING
Dilemma?” both jumpstarted the discussion of geoengineering and lent cred-
ibility to an idea that had until then existed largely in the shadows of academia.
Every serious researcher or policy expert who studies climate engineering,
including Crutzen, believes that cutting greenhouse gas emissions is at least as
important as developing geoengineering technologies, if not more urgent.
It is useful to consider abatement, carbon dioxide removal, and solar radiation
management in proper context with one another. In Figure 1, each large circular
element represents a process that drives the next step in the chain. The central items
are interventions that mitigate the impact between two linked terms; for example,
efficiency lowers the consumption of energy that results from consumption of
goods and services. Three abatement steps—using less energy (“conservation”),
using energy more efficiently (“efficiency”), and producing energy less carbon-
FIGURE 1 Connections among various factors in terms of the climate challenge. See text
for discussion. The round-tipped “arrow” between the “impacts on human systems” and
“desire for improved well-being” indicates that the former drives the latter. Reprinted with
permission from Caldeira et al., 2013.
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OVERVIEW OF CLIMATE ENGINEERING 7
intensively (“low-carbon energy”)—can together lower global greenhouse gas
emissions. Next are geoengineering options. The round-tipped “arrows” indicate
a more tenuous relationship than the other links.
As shown in Figure 1, CDR goes a step further than abatement. By pull-
ing gases out of the atmosphere it gets at the heart of the problem: if lowering
emissions is akin to reducing one’s exposure to a virus that causes a fever, CDR
is like using an antiviral medication. SRM is one step further still. It does not
change the level of CO2 in the atmosphere but instead serves to reduce its climatic
effects. Temperature is the most prominent of those effects, and SRM lowers the
planet’s thermostat by directly reducing the amount of solar energy absorbed
by the planet. Perhaps the metaphorical equivalent is using a cold compress to
alleviate fever.
Both CDR and SRM techniques attempt to mimic natural processes that
scientists mostly understand. But that is where their similarities end. In their
technical aspects, the political dynamics that might govern their deployment,
and their feasibility, the differences between them are stark. That’s one reason
that many scientists try to avoid using the terms “geoengineering” or “climate
engineering” to generalize between the two.
PLANETARY SUNBLOCK: SOLAR RADIATION MANAGEMENT
“Fast, cheap, imperfect and uncertain” is how Harvard physicist David Keith
(2011), one of the leading thinkers on both methods, describes SRM. The most
commonly explored technique for blocking sunlight from the planet is to mimic
the natural cooling effect of volcanoes by spreading sulfurous particles in the
stratosphere. The following paragraphs explain Keith’s characterization.
Fast: The 1991 eruption of the Mount Pinatubo volcano sprayed 5 million
tons of sulfur aerosol into the stratosphere as sulfur dioxide, which scattered
light away from Earth and cooled the planet by 0.5°C (Kravitz 2013). Modeling
studies (e.g., Caldeira and Matthews 2007) suggest that if a similar quantity of
sulfur aerosol were artificially injected into the stratosphere, the cooling could be
essentially instantaneous.
Cheap: A recent study by an aerospace research firm suggests that the costs of
deploying a global SRM scheme to offset anthropogenic warming “are comparable
to the yearly operations of a small airline” (McClellan et al. 2010).
Imperfect: A number of modeling studies have suggested various side effects
of this technique, including depriving the planet of solar energy that influences
rainfall, leading to less precipitation (Ricke et al. 2010). This effect could disrupt
the southeast Asian monsoon season or weather in South America, potentially
exacerbating droughts.
Uncertain: Many aspects of the climate system are not fully understood, so
tinkering with a fundamental variable that drives the system—the amount of solar
energy entering it—may have serious unexpected or unintended consequences.
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8 FRONTIERS OF ENGINEERING
Since Crutzen’s landmark paper, research into SRM has evolved from proof-
of-concept modeling into more sophisticated efforts. The Geoengineering Model
Intercomparison Project (GeoMIP) involves 19 different global climate models.
Each has run separate simulations with four standardized scenarios in which
solar radiation management is deployed in different ways (Kravitz et al. 2011).
Because different climate models employ different assumptions, characteristics,
and hysics, use of the same initial conditions, the thinking goes, may yield more
p
robust results about the environmental effects of various SRM strategies. One
example of the increasingly sophisticated modeling research on stratospheric
aerosols is a recent study that found that sulfate aerosols deployed to offset warm-
ing caused by a doubling of CO2 concentrations would make the sky 3 to 5 times
brighter—and less blue—than it is currently, which could affect photosynthesis
in plants and people’s psychological moods (Kravitz et al. 2012).
In the United States, David Keith and Harvard colleague James Anderson,
an atmospheric chemist, are planning “to develop in situ experiments to test the
risk and efficacy of aerosols in the stratosphere” (Keith 2012).
The most visible effort to explore stratospheric approaches through actual
experimentation is the Stratospheric Particle Injection for Climate Engineering
(SPICE) project, led by Bristol University and supported by the British govern-
ment at £1.6 million for 3½ years. Along with ongoing work to design particles
and computer modeling, the project originally included a planned field experiment
to spray 150 liters of water 1,000 meters in the air to test how a balloon would
behave in the wind during spraying, a feasibility test. The field experiment was
cancelled because of public concern about lack of regulations on SRM as well as
worries over a patent application that one of the research participants had filed
before receiving UK funds for the project (Watson 2012).
THINNING THE GREENHOUSE LAYER:
CARBON DIOXIDE REMOVAL
Scientists have proposed a variety of techniques for removing CO2 from
the atmosphere. These range from engineering forests to be more carbonaceous,
to growing massive algal blooms at sea, to sucking carbon dioxide out of the
atmosphere.
Few credible scientists believe CDR techniques to be a panacea. The approach
has attracted somewhat less attention and different kinds of controversy than SRM,
which Keith (2011) calls “slow, expensive and effective,” as explained below.
Slow: Global yearly emissions of CO2 are 34 million cubic metric tons,
resulting in an accumulation of 500 billion tons of anthropogenic CO 2 in the
atmosphere. Relying heavily on CDR as part of a climate response strategy means
creating a massive industry—perhaps the biggest engineering project in human
history—to steadily remove this mass of gas from the atmosphere one molecule
at a time.
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OVERVIEW OF CLIMATE ENGINEERING 9
Expensive: A 2011 study by the American Physical Society concluded that
collecting CO2 directly from the atmosphere “is not currently” economically
viable despite “optimistic” technical assumptions (APS 2011). It estimated that
the basic cost of a system that could be built today would be about $600/ton, an
order of magnitude more than the estimate for low-carbon energy sources.
Effective: CDR methods build off commercial techniques that work in sub-
marines and space shuttles to clean air of CO2 gas and promise fewer side effects
than SRM methods.
A number of startups are focusing on different techniques for CDR. In 2007
Sir Richard Branson launched a $25 million contest called the Virgin Earth
Challenge to encourage the development of technologies that “will result in the
net removal of anthropogenic, atmospheric greenhouse gases each year for at
least ten years without countervailing harmful effects.”1 The 11 contest finalists
represent a decent survey of leading commercial entities in this area, including
firms that propose to sequester carbon in biochar added to soil, to directly capture
atmospheric CO2 through chemical methods, or to burn biofuels and sequester the
resultant CO2 in the ground.
GEOENGINEERING RESEARCH POLICY AND
PUBLIC OPINION
Several European governments have supported organized programs to sup-
port climate engineering research. The United States has none. Studies on the
governance of climate engineering approaches are being conducted by a coalition
co-led by the UK Royal Society (SRM Governance Initiative), an Oxford Uni-
versity group on a two-year grant (Climate Geoengineering Governance project),
and the European Transdisciplinary Assessment of Climate Engineering project,
led by the Institute for Advanced Sustainability Science in Potsdam, Germany.
Meanwhile, work on the ethics of climate engineering has yielded, among
other things, the so-called “Oxford Principles,” proposed to restrict research into
SRM and CDR (Rayner et al. 2009). They include the following guidelines:
• That SRM be regulated as a public good
• That the public be involved in research related to SRM decisions, includ-
ing field experiments
• That research plans and results be transparent and shared publicly
• That bodies independent of researchers studying climate engineering
assess the environmental and socioeconomic impacts of research
• That decisions about deploying technology on a global scale be made only
when “robust governance structures” to oversee such efforts are in place.
1Virgin Earth Challenge announcement; posted online at www.virgin.com/subsites/virginearth/
(accessed July 28, 2012).
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10 FRONTIERS OF ENGINEERING
A number of expert panels (e.g., Long et al. 2011) have urged the United
States to create a dedicated research program in this area. But although the
National Science Foundation has supported a handful of studies on SRM, and
funds from various agencies have supported work applicable to CDR approaches,
there is no integrated, organized effort in the federal government.
Several studies exploring public opinion on climate engineering technolo-
gies have been published. In August 2011 Cardiff University released results of
a quantitative public engagement research project involving about 35 people that
met for a day and a half. “Very few people were unconditionally positive about
either the idea of geoengineering or the proposed [SPICE] field test. However,
most were willing to entertain the notion that the test as a research opportunity
should be pursued” (Parkhill and Pidgeon 2011).
An Internet poll of 3,105 American, Canadian, and British individuals pub-
lished in 2011 found that 8% and 45% of respondents, respectively, correctly
defined the interchangeable terms “geoengineering” and “climate engineering”
(Mercer et al. 2011). In the same survey, respondents were asked to rate statements
from 1, for “strongly disagree,” to 4, for “strongly agree.” For the statement “If
scientists find that Solar Radiation Management can reduce the impacts of global
warming with minimal side effects, then I would support its use,” the average
response was 3.01. The statement “Solar Radiation Management will help the
planet more than it will hurt it” received an average response of 2.49. The results
suggest that geoengineering could be viewed favorably by the public.
CONCLUSION
As the world’s population contends with the challenge of climate change,
respected scientists will continue studying climate engineering as part of a suite of
responses—the most important of which is the immediate curtailing of greenhouse
gas emissions. For policymakers and researchers in this area, the following con-
siderations will have to be taken into account: the need to address risks inherent to
the two types of climate engineering through research despite a lack of dedicated
funding for such work in the United States; the conduct of such studies, including
possible field studies, in an ethical way; and ongoing, open debate on the study
and use of climate engineering while mindful of public opinion, still nascent, on
the prospect of deploying the technology.
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