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Markkula Center for Applied Ethics

A Brief Introduction to Climate Engineering

A fleet of planes trailing aerosols.

A fleet of planes trailing aerosols.

Brad Zukeran ’24 and Shivani Dharanipragada ’25

Photo Credit: Richard R. Schunemann/Unsplash

Shivani Dharanipragada ‘25, is a computer science and economics major. Brad Zukeran ‘24 is pursuing a major in environmental science and minors in political science and history at Santa Clara University. Both were 2022-23 environmental ethics fellow at the Markkula Center for Applied Ethics. Views are their own.

As slowing climate change becomes a more and more daunting task, scientists have begun to look into an alternate solution: climate engineering. Climate engineering, according to Harvard’s Solar Geoengineering Program, is a broad category of technologies meant to alter the climate in order to reduce climate change. There are two main types of climate engineering: carbon dioxide removal and solar radiation management [1].

Carbon dioxide removal (CDR) is a concept many are familiar with. Technologies in this category attempt to change the atmosphere by removing carbon dioxide, which would “address the root cause of climate change — the accumulation of carbon dioxide in the atmosphere” [2]. One might think of this as an attempt to automate and/or accelerate what trees, other plants, plankton, and various photosynthesizing microbes do: absorb carbon dioxide. The U.S. Energy Department has identified several technologies that fit the description of carbon dioxide removal:

  • Direct air capture (DAC): captures carbon dioxide directly from the air [3]
  • Soil carbon sequestration: manages soils so they “absorb and hold more carbon” [4]
  • Biomass carbon removal and storage: a process in which biomass is converted into either useful products (like fuel) or directly into sequestered carbon (like charcoal), and carbon emissions from this conversion are “captured and stored in geological formations or … long-lasting products” [5]
  • Enhanced mineralization: accelerates weathering, or the process by which “various minerals absorb carbon dioxide” [6]
  • Ocean-based CDR: removing carbon dioxide from the ocean [7]
  • Afforestation/reforestation: planting more trees to accelerate natural carbon capture (US Forest Service) [8]

The most talked about of these technologies tend to be those based on direct air capture or reforestation.

The other major form of climate engineering is solar radiation management (SRM), which consists of reflecting solar radiation (sunlight) away from the Earth’s surface in order to reduce the amount of energy in the atmosphere. As this method does not include the reduction or collection of carbon dioxide emissions, it would be implemented as a temporary fix to buy time for potential long-term solutions. There are several proposed methods of solar geoengineering [1, 9]:

  • Stratospheric aerosol injection: consists of planes, balloons, or other means for releasing sulfur dioxide into the upper atmosphere to increase Earth’s albedo (solar reflectivity). This technology is inspired by major volcanic eruptions, like Mt. Pinatubo in 1991, which lowered the global temperature for a few years due to the spread of sulfur dioxide into the atmosphere. 
  • Marine cloud brightening: proposes large ships be retrofitted with emitters that would spray seawater into the atmosphere to assist in the development of especially reflective clouds. 
  • Cirrus cloud thinning: this method proposes to reduce high cirrus clouds in the atmosphere because they absorb more infrared radiation than they reflect. By introducing seeding aerosols, cirrus clouds can be reduced. 
  • Other means: painting urban areas lighter colors to reflect more light, orbital mirrors to reflect the sun away from Earth, ocean brightening by adding light-colored particles to the ocean, white artificial “icebergs” made of foam to reduce marine albedo, and so on.

Solar geoengineering is particularly controversial due to it being viewed as a “high risk, high reward” method of mitigating the effects of climate change, and because it is more of a “band-aid” solution that does not address the deeper issue of atmospheric composition.

As more geoengineering research is funded and the effects of climate change become more severe, the conversation surrounding the deployment of geoengineering solutions will surely become more prominent. With all of the possible unintended consequences and questions regarding its viability, the ethics of geoengineering should be explored. 

Below are two articles that ethically evaluate a few climate engineering issues.

Is climate engineering viable? And if it’s viable, is it ethical? By Shivani Dharanipragada ’25

An Ethical Evaluation of Stratospheric Aerosol Injection by Brad Zukeran ’24



[1] “Geoengineering.” Harvard’s Solar Geoengineering Research Program, 2023.    

[2] “Carbon Dioxide Removal.” Accessed June 9, 2023. 

[3] Lehnis, Marianne. “What Is Direct Air Capture and Why Should We Pay Attention?” Forbes, December 31, 2022. 

[4] “Fact Sheet: Soil Carbon Sequestration.” American University. Accessed June 9, 2023. 

[5] “Fact Sheet: Bioenergy with Carbon Capture and Storage (BECCS).” American University. Accessed June 9, 2023. 

[6] “Fact Sheet: Enhanced Mineralization.” American University. Accessed June 9, 2023. 

[7] Ghani, Maheera Abdul. “Ocean-Based Carbon Dioxide Removal (CDR) and Its Implications for the Sustainable Development Goals.” University of Cambridge - Centre for Science and Policy, November 18, 2022. 

[8] “Reforestation.” US Forest Service. Accessed June 9, 2023.  

[9] Daisy Dunne, “Explainer: Six ideas to limit global warming with solar geoengineering,Carbon Brief: Clean on Climate, 9 May 2018. 


Aug 17, 2023