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In this lesson, students will think critically about solar climate intervention — deliberate, large-scale efforts to cool Earth by increasing the reflection of solar radiation or increasing the emission of terrestrial radiation to space. This activity introduces the leading proposed methods, including stratospheric aerosol injection, marine cloud brightening, and cirrus cloud thinning, and centers on evaluating the benefits and risks of these strategies, including termination shock, moral hazard, and geopolitical conflict. Students will work in groups to develop their answers before sharing their findings with the class.
Needs review: The page title was changed from “Solar Climate Intervention” to say more about the lesson's approach, so teachers can tell the general introductions to solar radiation modification apart. The cover page keeps the author's title; confirm the new title with the author.
- Grade level
- Grades 11-12 (ages 16-18), Undergraduate
- Materials
- 8 resources available
- Questions?
- Contact the lesson team
Needs review before publishing
- 3 of the 12 images in these slides have no alt text, and slides 6 and 13 have no title. Add them (PowerPoint's Accessibility Checker lists each one) before publishing the file.
- Claude drafted the Global Connections section, and the global competence and UNESCO SDG 13 entries under Standards, from the lesson materials. Review and edit them.
- 11 of the 25 images in these slides have no alt text, and slides 14 and 19 have no title. Add them (PowerPoint's Accessibility Checker lists each one) before publishing the file.
- This version was the separate lesson “Geoengineering and Aerosol Interactions” (Jasper Kok's graduate lecture), merged here because the two lectures share their opening slides, video and readings. Confirm the merge with Jasper Kok.
- The page title was changed from “Solar Climate Intervention” to say more about the lesson's approach, so teachers can tell the general introductions to solar radiation modification apart. The cover page keeps the author's title; confirm the new title with the author.
Overview
Objectives
By participating fully in this activity, students will learn how to:
- Explain what solar climate intervention is, how it differs from carbon dioxide removal and greenhouse gas mitigation, and describe the leading proposed methods (stratospheric aerosol injection, marine cloud brightening, cirrus cloud thinning)
- Evaluate the primary benefit of solar climate intervention — reduction in climate damages — against its major risks, including termination shock, moral hazard, and geopolitical conflict
- Assess the evidence for and against the “moral hazard” argument, that the availability of climate engineering methods undermines society’s commitment to emissions mitigation
- Discuss the governance challenges of solar climate intervention, including who would control deployment and how it could spark international conflict
Grade Level
Grades 11-12, Undergraduate
Standards
These are Next Generation Science Standards (NGSS) performance expectations.
- HS-ESS3-4 — Evaluate or refine a technological solution that reduces impacts of human activities on natural systems, with the clarification statement explicitly naming large-scale geoengineering design solutions (such as altering global temperatures by making large changes to the atmosphere or ocean) as an example.
- HS-ESS3-1 — Construct an explanation based on evidence for how the availability of natural resources, occurrence of natural hazards, and changes in climate have influenced human activity.
- HS-ETS1-3 — Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics, as well as possible social, cultural, and environmental impacts.
This lesson also supports these international frameworks:
- Global competence (Asia Society and OECD): Investigate the world; Recognize perspectives
- UNESCO learning objectives for SDG 13 (Climate Action):
- Cognitive 5: prevention, mitigation and adaptation strategies
- Socio-emotional 1: explaining ecosystem dynamics and the impacts of climate change
- Behavioural 3: assessing the impact of decisions on other people and world regions
- Behavioural 4: promoting climate-protecting public policies
United Nations Sustainable Development Goals
- SDG 13 — Climate Action: Take urgent action to combat climate change and its impacts
- SDG 16 — Peace, Justice and Strong Institutions: Promote peaceful and inclusive societies for sustainable development, provide access to justice for all and build effective, accountable and inclusive institutions at all levels
Materials Required
- PowerPoint slideshow “UCLA upper level ugrad class - climate intervention guest lecture.pptx”
- Video, “Geoengineering: A Horrible Idea We Might Have to Do” https://www.youtube.com/watch?v=dSu5sXmsur4
- Paper and pencil
Learning Sequence
Lesson Plan Introduction
As the world falls behind on the emissions cuts needed to meet the Paris Agreement's targets, this lesson explores solar climate intervention — deliberately reflecting sunlight back to space — and asks students to weigh its potential benefits against its risks and governance challenges.
Activity Details
What is solar climate intervention?
- Introduce solar climate intervention as deliberate, large-scale manipulation of the planet to cool Earth, either by increasing reflection of solar radiation or increasing emission of terrestrial radiation to space (also called solar radiation management).
- Distinguish it from carbon dioxide removal (CDR), and introduce the three leading methods: stratospheric aerosol injection (SAI), marine cloud brightening (MCB), and cirrus cloud thinning (CCT).
Context: current warming and the Paris Agreement
- Present current global warming levels and CO₂ emissions trends, and discuss why the world is unlikely to meet the Paris Agreement’s 1.5°C and 2°C targets.
- Ask students: what would it mean for society if we pass 1.5°C or 2°C of warming?
Video
- Play the Kurzgesagt clip on geoengineering, "Geoengineering: A Horrible Idea We Might Have to Do."
Discussion: initial risks and benefits
- Before presenting any specific benefits or risks, have students take a few minutes to write down what they think are the main benefits and the main risks or downsides of solar geoengineering (and specifically stratospheric aerosol injection), then discuss with a neighbor.
Benefit #1: Reduction in climate damages
- Present evidence on the likely reduction in climate damages from anything from sea level rise to extreme storms to heat waves and food insecurity, and discuss why this reduction is likely much larger than the cost of deployment (roughly $10–100B per 1K cooling/year).
- Discuss the implication that this low cost means a single state, company, or even individual could unilaterally choose to deploy solar geoengineering.
Risk #1: Termination shock
- Discuss termination shock: if solar climate intervention were suddenly stopped, temperatures could rise far more rapidly than they would have in the absence of intervention.
- Discuss why this means solar climate intervention can only be considered a temporary measure that must be maintained (or carefully phased out) once started — never a stand-alone solution.
Benefit #2: Buying time to transition to a carbon-free economy
- Discuss how solar geoengineering could temporarily reduce climate damages while the world transitions to net-zero emissions, and reemphasize that it should never be used instead of cutting emissions.
Risk #2: Moral hazard
- Introduce the “moral hazard” concept: the idea that the availability of climate engineering methods could undermine society’s or individuals’ commitment to mitigation efforts.
- Discuss the NASEM (2021) finding that, despite persistent concern about this deterrence effect, social science research examining it is equivocal — and some studies suggest individuals may actually increase their mitigation commitment when geoengineering is introduced.
Risk #3: Geopolitical conflicts
- Discuss the governance uncertainty around solar climate intervention: whose hand would control the thermostat, and what happens if intervention causes (or is perceived to cause) damaging changes in weather patterns elsewhere?
- Discuss both directions of the conflict question: could deployment itself spark geopolitical conflict, and could reducing climate damages instead reduce other drivers of conflict, like resource scarcity and climate refugees?
Conclusion
Close with a values-based question: if the world continues cutting emissions but not fast enough to avoid passing 2°C warming by 2050, should the US (or the world) use climate intervention? Why or why not?
Global Connections
Needs review: Claude drafted the Global Connections section, and the global competence and UNESCO SDG 13 entries under Standards, from the lesson materials. Review and edit them.
Start where you teach
Ask students what passing 1.5°C or 2°C of warming would mean for their own community, using local examples of heat, water or food.
Bring in other perspectives
The closing question asks whether the US or the world should use solar climate intervention. Ask it from several countries' points of view instead, including those likely to be most affected and least consulted.
Share beyond the classroom
Groups can present their answer to the governance question as a short policy brief for a local or national decision maker.
Lesson materials
Download the files below to teach this lesson. PDFs are accessible versions; PowerPoint and Excel files can be edited for your class.
Teacher resources
Lesson slides
Needs review: 3 of the 12 images in these slides have no alt text, and slides 6 and 13 have no title. Add them (PowerPoint's Accessibility Checker lists each one) before publishing the file.
Graduate version: lesson slides
Needs review: 11 of the 25 images in these slides have no alt text, and slides 14 and 19 have no title. Add them (PowerPoint's Accessibility Checker lists each one) before publishing the file.
Slides for the “Graduate version: aerosol physics and a quantitative exercise” version below.
Geoengineering: A Horrible Idea We Might Have to Do
Optional. Kurzgesagt – In a Nutshell's animated introduction to solar geoengineering, used to open the lesson. It is on YouTube only and can't be downloaded here; where YouTube isn't available, open with the lesson slides and the discussion instead.
Stratospheric Aerosol Injection
How SAI works, the Pinatubo analogy, and the stratosphere's role.
Marine Cloud Brightening
Particle size, ship-based spraying, and MCB's regional-cooling trade-offs.
What Is Termination Shock?
A plain-language explainer on the risk, including what would/wouldn't trigger it.
SRM360: The Case for a Solar Geoengineering Research Governance Platform
Accessible overview of why governance is a gap and what's being proposed to fill it.
NASEM (2021), Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance
The source of the moral hazard discussion, including the finding that deterrence evidence is equivocal.
Other ways to teach this lesson
Graduate version: aerosol physics and a quantitative exercise
Needs review: This version was the separate lesson “Geoengineering and Aerosol Interactions” (Jasper Kok's graduate lecture), merged here because the two lectures share their opening slides, video and readings. Confirm the merge with Jasper Kok.
Jasper Kok's graduate lecture on the same topic goes deeper into the physics. Students think critically about the aerosol interactions that let stratospheric aerosol injection (SAI) and, to a lesser extent, marine cloud brightening (MCB) reflect sunlight, through about 15 discussion questions and a quantitative exercise, before turning to risks, benefits and governance. It opens with the same slides and video as the lesson above; use the “Graduate version: lesson slides” in Lesson materials.
Objectives
By participating fully in this activity, students will learn how to:
- Explain the physical mechanisms by which stratospheric aerosols and marine cloud brightening reflect incoming solar radiation, and how aerosol microphysics (particle size, optical depth, cloud condensation nuclei) governs their cooling efficiency
- Quantitatively estimate the stratospheric aerosol optical depth needed to offset a given radiative forcing, using basic radiative balance relationships
- Evaluate the risks and benefits of solar geoengineering strategies, including termination shock, ozone depletion, and hydrological cycle changes, weighed against reduced climate damages
- Discuss the governance and geopolitical challenges of climate intervention, including who might deploy it and the potential for international conflict
Lesson plan introduction
As the world falls behind on the emissions cuts needed to meet the Paris Agreement's targets, this lesson explores climate intervention — deliberately reflecting sunlight back to space — through a series of discussions on the science, risks, and governance of these strategies.
Activity details
Video & recap
- Play the Kurzgesagt clip on geoengineering - “Geoengineering: A Horrible Idea We Might Have to Do” https://www.youtube.com/watch?v=dSu5sXmsur4
- Discuss why SAI is a plausible near-term option: it's relatively cheap, so a single nation or small group of nations could deploy it. Cover its potential to reduce climate damages, its major risks, and why it should only be used to buy time — never as a substitute for emissions cuts (termination shock).
How SAI works
- Introduce the mechanism: SAI emulates a large volcanic eruption by injecting SO₂ into the stratosphere, where it forms sulfate aerosols with a residence time of ~1–3 years.
- Show the global dimming record from past volcanic eruptions (e.g., Pinatubo) as real-world evidence of this cooling effect.
Quantitative exercise
- In small groups, students estimate the stratospheric aerosol optical depth needed to counter the radiative forcing from a doubling of CO₂, using the provided values (solar constant, forcing per doubling, aerosol backscatter fraction, Earth's albedo).
- Groups compare their answer to typical tropospheric aerosol optical depth and discuss how SAI at that magnitude would visibly change the sky, including at sunset.
Discussion round 1: Feasibility and system behavior
- Groups work through questions on the climate system's thermal inertia and why sustained negative forcing is needed to maintain cooling, and whether SAI is technically and financially feasible at scale.
- Groups also consider why aerosols have shorter lifetimes at higher latitudes (Brewer-Dobson circulation).
Discussion round 2: SAI vs. volcanic eruptions
- Groups compare how the climate would respond to a slow, sustained, multi-latitude SAI deployment versus a sudden, single-latitude volcanic eruption, then discuss the resulting differences in ocean-land temperature gradients and response timescales.
Discussion round 3: Cooling efficiency
- Groups discuss why cooling efficiency (per unit of SO₂ injected) decreases as more SO₂ is added — covering particle growth, condensation sink effects, and reduced scattering efficiency at larger particle sizes.
SO₂ vs. H₂SO₄ injection
- Groups compare the trade-offs of injecting SO₂ gas versus H₂SO₄ liquid directly, weighing ease of transport against control over resulting particle size.
Marine Cloud Brightening
- Groups discuss why smaller sea-salt particles (under ~100 μm) are more effective for MCB per unit mass released, and how particle size drives the trade-off between cloud droplet number, albedo, and cloud lifetime.
Regional climate effects
- Groups discuss how the resulting climate under SAI would differ regionally from a world with equivalent GHG-driven warming (e.g., ocean vs. land temperature change, seasonal and hemispheric precipitation patterns).
Risks, benefits & governance
- Groups list the main benefits (reduced climate damages) and risks (termination shock, geopolitical conflict, unknown unknowns) of climate intervention.
Conclusion
Close with a values-based question: given current emissions trends, should the US or the world use climate intervention — and who should decide?
Related lessons
- Managing Climate Overshoot: Where Solar Radiation Management Fits in the Climate Toolkit: another introduction to solar radiation modification, comparing it with emissions cuts, carbon removal and adaptation
- Reflecting Sunlight to Cool Earth: Evidence from Climate Models and Volcanic Eruptions: another introduction to solar radiation modification, built on climate model results and past volcanic eruptions
- Climate Change and Solar Radiation Modification: Science, Risks, and Who Decides: another introduction to solar radiation modification, from the state of the climate to governance, with a science–policy role-play version
- Climate Adaptation and Intervention: Wildfire Resilience and Solar Radiation Management: another introduction to solar radiation modification, framed around adapting to growing wildfire risk
Credit and contact
Credit
Created by Jasper Kok, PhD, University of California, Los Angeles.
Contact
Questions about this lesson, or need a file in another format? Contact:
- Jasper Kok – jfkok@ucla.edu