by Katie Dagon

Imagine if we had an “undo” button for climate change – we could remove all the greenhouse gases from the air or cool the planet’s temperature in an instant. While this might sound like science fiction, the basic idea is not as far off as you might think. Reducing fossil fuel use is really important, but also really difficult. And even if we work quickly to limit greenhouse gas emissions, the carbon dioxide that is already in the atmosphere will influence our climate for thousands of years to come. Fixing problems related to climate change will likely require a wide range of solutions. That’s why scientists and policymakers are exploring how intentional climate interventions, also called geoengineering or climate engineering, can help us combat the worst effects of climate change.

While geoengineering is slowly gaining exposure in the science and policy worlds, it’s actually not a brand new idea. The first mention of something like climate engineering dates back to a 1965 report by the President’s Science Advisory Committee to President Lyndon Johnson. The committee warned that climate changes from increasing atmospheric carbon dioxide could be harmful, and “the possibilities of deliberately bringing about countervailing climatic changes” should be explored. More recently, an article in 2006 by the Nobel Prize-winning atmospheric chemist Paul Crutzen prompted a resurgence of the idea in the scientific community. And just last year, the National Academies came out with two reports on geoengineering that moved the discussion further into the policy realm.

The two National Academies reports represent the typical grouping of climate engineering into two broad categories: solar geoengineering and carbon dioxide removal. While both categories encompass a wide range of ideas, they are fundamentally different because they target different areas of the climate system.

Figure 1: Schematic of some geoengineering ideas, including both solar geoengineering (e.g. aerosols in the stratosphere, giant reflectors in orbit) and carbon sequestration (e.g. grow trees, pump liquid CO2 into deep sea/rocks). (Source: Keith 2001)
Figure 1: Schematic of some geoengineering ideas, including both solar geoengineering (e.g. reflective aerosols, space mirrors) and carbon dioxide removal (e.g. afforestation, CO2 air capture). Figure by Rita Erven/Kiel-Earth-Institute.

Reflecting Sunlight

Solar geoengineering is also often called solar radiation management, and it focuses on techniques that decrease the amount of sunlight reaching the Earth’s surface to cool the planet. These ideas all aim to increase reflectivity through methods such as large mirrors in space or injecting reflective aerosols into the upper atmosphere. Sounds crazy, right? But we know that aerosol injection works because volcanoes mimic the same process. Explosive eruptions emit enough sulfur dioxide (which then forms reflective sulfate aerosols) to have a measureable effect on global temperature. The 1991 eruption of Mount Pinatubo in the Philippines produced enough aerosol to cool the global temperature by roughly 0.5°C (~1°F) in the year following the eruption. The even larger 1815 eruption of Mount Tambora in Indonesia produced such a noticeable climate effect that the year following the eruption became known as the “Year Without Summer,” during which crop losses resulted in widespread famine.

Figure 2: The 1991 eruption of Mount Pinatubo in the Philippines. (Source: USGS)
Figure 2: The 1991 eruption of Mount Pinatubo in the Philippines. (Source: USGS)

The first question you might ask about solar geoengineering is: who sets the thermostat? It’s not clear that one region of the world would want the climate cooled as much as another region. This is why geoengineering is often referred to as a “free driver” problem, because a small set of individuals or nations could decide to implement it, and the outcome would affect the whole planet. This is in contrast with climate change, which is considered a “free rider” problem in that it requires global cooperation. One country could take steps to reduce emissions, while another country does nothing and receives the benefits for free.

Injecting reflective aerosols into the upper atmosphere is relatively cheap compared to the massive global problem that is changing our energy system to reduce our dependence on fossil fuels. But we also need to understand the risks or any unintended consequences. Solar geoengineering might cool the planet just like a volcanic eruption, but we don’t know everything else it would do to the climate system. However, while solar geoengineering isn’t an alternative to emissions reductions, it has the potential to buy time and reduce short-term impacts. Understanding these tradeoffs is a key pursuit of current research.

Removing Carbon Dioxide

Last month, measurements of carbon dioxide in the atmosphere reached 400 parts per million. Monthly values will very likely not fall below this level for the rest of our lifetimes, and beyond. While solar geoengineering addresses the climate effects of greenhouse gases, what about getting rid of carbon dioxide, the most important greenhouse gas, directly? This is commonly referred to as carbon capture and storage (CCS). There are 15 large-scale CCS projects worldwide that capture about 28 million tons of CO2 per year, or 0.08% of global fossil fuel emissions. Many of those projects even use the captured CO2 for enhanced oil recovery, a process that pumps CO2 through semi-depleted oil wells to produce more oil. There are some CCS projects that aim to capture CO2 at power plants, including plants that burn both fossil fuels and biomass. Capturing CO2 produced by biomass can result in what’s called negative emissions, because the CO2 is captured from the land-atmosphere system and permanently sequestered.

Direct capture of CO2 from the atmosphere is harder than at a stationary source because the background concentration is much lower. It’s easier to have a constant source of CO2 from something like a coal-fired power plant. Despite this challenge, there are companies aiming to make air capture feasible through the chemical extraction of CO2 gas from the air. The pure CO2 can then be used for industrial applications or permanently stored. However, at present these technologies are expensive and need to be scaled up in order to put a sizeable dent into carbon emissions.

Figure 3: A circular representation of strategies for addressing climate change, including geoengineering.
Figure 3: A circular representation of strategies for addressing climate change, including geoengineering. Adapted from here. Figure by Mike McArthur.

Looking Ahead

Though climate forecasts often look bleak, geoengineering offers a glimmer of hope for the future. Making the planet a little cooler through solar geoengineering is a fast growing area of research with a lot of potential, though it is not a permanent solution. Removing carbon dioxide from the atmosphere could counteract damage that’s already been done, though it needs to be scaled up considerably. Together, the two techniques can be used to complement each other effectively.

Policy scenarios rely on negative emissions technologies such as geoengineering to reach the 1.5°C global temperature goal cited in the Paris climate agreement last December. Most experts agree there is no quick fix, but we should research and pursue a portfolio of technologies for the best bet to limit global temperature rise. However, scaling up any effort to make a serious impact on climate change will take great effort and resolve on behalf of policymakers and scientists alike. Hard work will need to be done and difficult questions will need to be answered to discover the powerful potential geoengineering has to offer.

Katie Dagon is a PhD Candidate in the Department of Earth and Planetary Sciences at Harvard. Her research focuses on modeling the impacts of climate change and solar geoengineering on land-atmosphere water cycling and climate extremes. Find her on twitter @katiedagon.

This article is part of our Special Edition: Dear Madam/Mister President.

For More Information: 

Geoengineering the climate: science, governance and uncertainty, The Royal Society, 2009

The Science of Geoengineering, Caldeira, K. et al., Annual Review of Earth and Planetary Sciences, 2013

Climate Intervention: Reflecting Sunlight to Cool the Earth, National Academies, 2015

Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, National Academies, 2015

Cover image adapted from Rita Erven/Kiel-Earth-Institute.






8 thoughts on “Engineering the Earth to Fight Climate Change

  1. Dear Katie,
    nice blog article. For figure one you wrote “(Source: Keith 2001)”, which is misleading. The figure was produced by Rita Erven, who works for the German SPP 1689. She gave this figure to the community under Creative Commons. So giving David Keith the credit is not right. Maybe this was not your intention.

  2. Who hell gives you permission to spray heavy metals into the air and fuck up a blue sky?

    A class action suit is coming, so just keep telling the public lies. I hope the originations against climate eng get their day in court. You piece of fucking shit. I hope David Keith burns in hell!!!!!!!

  3. I agree with you jb. They have been lying to us for decades. These programs were implemented a long time ago using toxic heavy metals that kill all life on earth. They are only now going public because it has become impossible for them to hide this crime from the people. All involved in these crimes against humanity need to be rounded up and jailed immediately. Go to to learn the truth about their true agenda.

  4. paticaLife of CO2 in atmosphere is 100 years and not 1000 years.Some other greenhouse gases have life 1000 years and more hence total greenhouse gases in atmosphere is expressed in terms of CO2 equivalent o in short C-equivalent. Carbon equivalent of gas is expressed as million tons of Carbon dioxide equivalent = million tons of particular gas x global warming potential(GWP)
    Secondly the propellent gas in aerosol is still CFC in most parts of the world which remove ozone from protective atmospheric ozone layer making ozone holes
    Nature has perfected over million years in maintaining optimum level of carbon dioxide in atmosphere by circulating through its other 3 spheres of activities,(geosphere,hydrosphere, biosphere).However CO2 generated in anthrosphere is increasing its content in atmosphere and rate of global temperature.Anthrospheric activities mainly industries are responsible for global warming and key technology to reduce the rate is through green or eco-engineering I have spent four decades on research and field work in industries in this areas and have written four unique series books ,excepting one on global warming published in India rest 3 have been published in USA by prominent publishing houses, recent featured articles in leading engineering journals in USA.Green engineering efforts can reduce CO2 emission by minimum 10% and more without even using clean energy.
    It would be good for any researchers looking for pragmatic solution to global warming to read this unique series By the way one of the books have a chapter on Geo-engineering

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