State of the Planet

News from the Columbia Climate School


The Double-Edged Sword of Geoengineering

Photo: Chris Woodford/Explain that based on NASA’s 1972 photo Full Earth, courtesy of NASA Johnson Space Center.

Shooting sulfur particles into the stratosphere to reflect the sun?  Dumping iron into the ocean to boost the absorption of carbon dioxide? Could these far-fetched and dangerous-sounding schemes help avert potentially catastrophic effects of climate change, or would they exacerbate conditions on our ever warming planet? These strategies, which involve the deliberate and large-scale intervention in our climate system to moderate global warming, are known as geoengineering. Fantastical as they seem, billionaires Bill Gates, Sir Richard Branson and others, are investing millions of dollars into the geoengineering research of a few leading climate scientists like Ken Caldeira at Stanford. At first, Caldeira thought geoengineering sounded crazy too, but his research showed that it would basically work.

If global warming exceeds 2˚ C, it would be “a prescription for disaster,” said NASA scientist James Hansen. To prevent this from happening, we need to cap atmospheric carbon dioxide levels at 350 parts per million; but in March 2012, we reached almost 394.5 ppm and global greenhouse gas emissions continue to rise. Even if we were able to immediately cut greenhouse gas emissions to zero, however, global warming would continue for the foreseeable future because carbon dioxide remains in the atmosphere for several hundred years. Moreover, the international community has failed to reach an agreement that tackles the fundamental problem of controlling carbon emissions and prospects for doing so don’t look good. As a result, geoengineering is beginning to sound less like science fiction to some, and more like a possible Plan B.

Geoengineering strategies fall into two main categories:

  • Solar radiation management, which seeks to reduce the amount of sunlight that reaches earth by deflecting it or increasing Earth’s reflectivity (albedo).
  • Carbon dioxide removal, which tries to take carbon dioxide out of the atmosphere.

Solar radiation management includes efforts like white roofs that deflect sunlight, brightening clouds by shooting seawater into them to increase their albedo (salt provides the nuclei that seed the clouds), and controversial strategies based on the cooling effect that can follow major volcanic eruptions.

In 1991, Mt. Pinatubo in the Philippines erupted, sending 22 million tons of sulfur dioxide into the stratosphere. The sulfur particles scattered around the globe, deflected sunlight, and cooled Earth by 0.4 to 0.5˚ C. Solar radiation management would recreate this effect by using balloons, aircraft or cannons to shoot tiny reflective particles like sulfates into the stratosphere to temporarily block sunlight.

The 1992 Panel on Policy Implications of Greenhouse Warming calculated that this strategy would cost just pennies per ton of carbon dioxide mitigated. It would also be fast-acting, capable of quickly reducing the impacts of heat stress on crops, resulting in increased productivity since carbon dioxide levels, which boost growth, would remain high.

Other solar radiation management ideas include the use of engineered nanoparticles, which could be constructed to ascend high into the atmosphere and keep their shiny side to the sun, and sunshades in space made of mirrors.

Solar radiation management would do nothing to address the root cause of global warming—carbon dioxide emissions—or ocean acidification caused by the sea’s absorption of excess carbon dioxide. And while stratospheric aerosols could theoretically produce cooling on a local or global level, they might also create regional problems by affecting rain and snowfall patterns and causing drought. According to Caldeira, a year or two after Mt. Pinatubo, when aerosols dropped from the stratosphere, both the Amazon River and the Ganges had very low flows and droughts occurred. A 2010 study by ETC (Erosion, Technology and Concentration), an international group that opposes geoengineering, states that solar radiation management climate models show a risk of increased drought over Africa, Asia and the Amazon jungle.

Putting sulfate particles into the stratosphere could also damage the ozone layer, lead to acid rain and increased ocean acidification, and interfere with solar cells, astronomy and satellites. In addition, solar radiation management techniques carry the risk of a rapid rise in temperature if the program were started then stopped, which would be more dangerous to life on Earth than a gradual temperature rise.


Carbon dioxide removal strategies reduce greenhouse gases in the atmosphere, or attempt to manipulate natural processes to remove greenhouse gases indirectly. While they tackle the fundamental problem of carbon emissions, and address ocean acidification, they would require many years to fully take effect.

Carbon dioxide removal techniques include tree planting, creating biochar (charcoal) and burying it to increase carbon sequestration, carbon capture and storage, adding carbonate to the ocean to increase carbon dioxide uptake, and capturing carbon from the air. Klaus Lackner, Director of the Earth Institute’s Lenfest Center for Sustainable Energy, is developing an “artificial tree” that removes carbon dioxide from the air. Ocean fertilization is perhaps the most controversial carbon dioxide removal strategy of all.

Phytoplankton blooms in the South Atlantic

Through photosynthesis, phytoplankton in the ocean absorbs half the carbon dioxide taken up annually by all of Earth’s plants. Ocean fertilization involves depositing nutrients (iron, nitrogen or phosphorus) into areas of the ocean lacking one of these key nutrients to stimulate the growth of phytoplankton and increase the absorption of carbon dioxide, which is then carried to the ocean floor when the phytoplankton die.

Critics say ocean fertilization could alter food webs; deplete oxygen at deeper ocean levels; produce eutrophication, dead zones and toxic algal blooms; increase ocean acidification in the deep sea; and impact coral reefs. While the cost of ocean fertilization would be relatively low, Britain’s Royal Society says that none of the various carbon dioxide removal methods assessed have proven to be effective at an affordable cost with acceptable side effects.

Most geoengineering research today is being done with climate models and mapping; few field tests have been conducted. The Fund for Innovative Climate and Energy Research, run by David Keith of Harvard and Ken Caldeira and funded by Bill Gates’ personal funds, has given out $4.6 million for research on climate modeling, technical feasibility, governance, potential and risks, but it does not support field-testing methods like solar radiation management and ocean fertilization that would actually interfere with the climate system. ETC argues that geoengineering cannot be tested because in order to truly assess its effect on the climate, it would need to be deployed on a massive scale, which would likely also have massive repercussions.

Germany, India, Canada, Russia and Britain are studying geoengineering, and more countries will soon be capable of it as well. In 2009, a German-Indian government-sponsored experiment (LOHAFEX) dumped 6.6 tons of iron into 300 square kilometers of the South Atlantic. There was a burst of algae growth, but within two weeks, the algae was eaten by small crustaceans, so less carbon dioxide was absorbed than anticipated.

SPICE. Photo credit: Hugh Hunt

In October 2011, a British project called SPICE (Stratospheric Particle Injection for Climate Engineering) was scheduled to test a delivery system using a tethered balloon and hose to deliver water one kilometer into the sky. It was put on hold due to opposition from environmental groups.

Geoengineering opponents cite many risks. Strategies could be ineffective or incomplete. The technology could fall prey to mechanical failure, human error, natural disasters or terrorism, and lead to devastating and/or irreversible disruption of the climate system. Many want to ban geoengineering research for fear it would reduce the imperative to cut greenhouse gas emissions.

Scott Barrett, Lenfest-Earth Institute professor of natural resource economics at Columbia University, takes issue with this point. “People worry that if we use geoengineering, we wouldn’t reduce our greenhouse gas emissions. But we’re not reducing them anyway…And given that we have failed to address climate change, I think we’re better off having the possibility of geoengineering…However it does raise the question of do we have the wisdom and institutions to use it wisely?”

Governance is perhaps the thorniest aspect of geoengineering. Because geoengineering is a relatively cheap way to address climate change, it is unilateral—rich countries and billionaires could finance it on their own—yet the consequences would be global. Who then should get to control geoengineering, and under what governance? Some strategies would benefit certain countries and harm others, so who would have the right to decide whether, when and how to use it? Geoengineering would likely create winners and losers—should losers be compensated? Could conflicts lead to geoengineering wars?

While there are various international treaties, aspects of which could limit some geoengineering experiments, there is no overarching regulatory framework that governs the broad use of geoengineering technology.

In October 2010, the U.N. Convention on Biological Diversity adopted a moratorium on geoengineering activities that could threaten biodiversity (the United States has not ratified the convention). ETC is pushing for a comprehensive test ban on geoengineering at Rio+20, the U.N. Conference on Sustainable Development in June.

The 2009 geoengineering report by Britain’s Royal Society calls for an international body to review mechanisms that could regulate geoengineering, and for scientific organizations to develop guidelines for research and evaluate benefits and environmental effects.

“The central problem for the governance of geoengineering,” the report says, “is that while potential problems can be identified with all geoengineering technologies, these can only be resolved through research, development and demonstration… Ideally, appropriate safeguards would be put in place during the early stages of the development of any new technology.”

Barrett, an expert in international agreements, believes a geoengineering agreement should focus on what countries should do and what they can agree upon. He contends that an agreement should simply require a country intent on engaging in geoengineering, from field research to larger experiments, to let the world know. This would enable other countries to react or discuss the situation beforehand, make deals or participate, and avoid conflicts. It would also encourage collaborative research and development. Countries would be willing to sign on because they would know that other nations would also have to declare their intentions. If an agreement were too restrictive, or included a ban or veto power, Barrett says, countries that wanted to proceed with geoengineering would simply walk away from the table.

Despite the risks and uncertainties of geoengineering, many scientists believe we must study the options to ensure that damaging actions are not taken in haste in the future. The Royal Society recommends that further research and development of geoengineering be undertaken, but that policies also continue to focus on reducing carbon emissions and adaptation. It stresses the importance of placing all concerns about geoengineering in the larger context of climate change impacts that would otherwise be likely to occur anyway and comparing the relative risks and potential benefits.

“Imagine some point in the future when things are starting to go very wrong. And turning down the sun would have a good chance of limiting damage. Would you really not want to know if the technology worked and what its side effects were?” Barrett asked. “Even if we were to ban geoengineering today, if things get bad in the future, they’d do it anyway…would you want the future to be ignorant?”

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12 years ago

The SPICE project was recently cancelled because of a lack of rules governing geoengineering experiments, a potential conflict of interest over a patent application for some of the technology involved and the need for more public involvement.

11 years ago

[…] resource economics at Columbia University, said in an interview published on the school’s Earth Institutes blog. “But we’re not reducing them anyway… And given that we have failed to address climate […]

Lauren Ayers
Lauren Ayers
7 years ago

How to reverse climate change!

Mycorrhizal fungi pulls more CO2 from the atmosphere than any other method. In 15-20 years it could get us back to 350 ppm from the human-caused 400+ it is now.

Regenerative Agriculture practitioners found humanity’s 10,000-year-old mistake: plowing. Turning the soil kills the mycorrhizal fungi that, in nature, coat every root hair and bring minerals to the plant in exchange for 20 to 50% of the sugars photosynthesized by the plant.

David Johnson, PhD, of the U. of New Mexico, finds that inoculating cover crops on only half of the world’s fallow land would sequester enough CO2 without having to resort to methods that the Precautionary Principle would disallow, such as aluminum oxide nano particles being sprinkled from above, which makes soil toxic to for crops and all other plants, and which makes rain water also toxic for living things.

Tests show that using fungi costs less and works faster, on a big enough scale, than any other method. Plus, using fungi doubles yields with no extra water, makes ‘traditional’ seeds outperform GMO seeds, and ends the need for nitrate fertilizer.

Dr. Johnson’s talk at Chico State, including charts and graphs: