Climate Change and Solar Radiation Modification: Science, Risks, and Who Decides

Overview

Objectives

By participating fully in this activity, students will learn how to:

• Describe the current state of global warming (record-warm years, tipping points, water security) and explain why exceeding 1.5°C carries serious risks
• Distinguish between mitigation, adaptation, and climate intervention (carbon dioxide removal and solar radiation modification) as different strategies for responding to climate change
• Explain how the three main SRM methods — stratospheric aerosol injection (SAI), marine cloud brightening (MCB), and cirrus cloud thinning (CCT) — work, and why their scale of action differs (global vs. local)
• Evaluate the benefits and risks associated with SRM research, including regional climate effects and the risk of termination shock
• Discuss the governance challenges that make SRM difficult to regulate internationally, including its disproportionate potential impact on the Global North versus the Global South

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; Communicate ideas
• UNESCO learning objectives for SDG 13 (Climate Action):
  • Cognitive 2: current climate change as caused by human greenhouse gas emissions
  • Cognitive 4: the ecological, social, cultural and economic consequences of climate change
  • Cognitive 5: prevention, mitigation and adaptation strategies
  • 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 6 — Clean Water and Sanitation: Ensure availability and sustainable management of water for all — directly relevant to the “water bankruptcy” crisis discussed in this lecture
• 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

• PDF slideshow "2026_04_24_ClimateChange-SRM_IAG_F.pdf" (Climate Change & Climate Intervention, Prof. Michelle Simões Reboita, Universidade Federal de Itajubá – UNIFEI)
• Paper and pencil
• This discussion guide, since the lecture slides do not include built-in discussion prompts

Learning Sequence

Lesson Plan Introduction

As record-breaking warm years accumulate and water systems show signs of collapse, this lesson examines the tools available to respond to climate change — mitigation, adaptation, and climate intervention — and asks students to weigh the promise of solar radiation modification against its risks and unresolved governance gaps.

Activity Details

1. The Current State of the Climate — and Why It Matters (Slides 3–7)

• Present the temperature record (slides 3–4): 2024, 2023, and 2025 were the three warmest years on record, all within the last three years, and 2023–2025 was the first three-year period to average above 1.5°C.
• Show the tipping points, ecosystem, and extreme-weather risks of exceeding 1.5°C (slide 5), and the emerging global “water bankruptcy” crisis (slides 6–7), where water systems can no longer naturally recover to historical baselines.
• Discussion: (Ask after slide 4) 2024, 2023, and 2025 are the three warmest years on record, and all three happened in the last three years. What does this tell you about the pace of climate change?
• Discussion: (Ask after slide 7) The water bankruptcy diagram shows how scarce water availability can cascade into higher food prices and socioeconomic instability. Why might a water crisis in one region eventually affect people far away?

2. Three Ways to Respond to Climate Change (Slides 8–12)

• Introduce mitigation and adaptation (slides 8–9), noting that even if emissions stopped today, surface temperature would take thousands of years to cool back to pre-industrial levels, and that adaptation alone requires investment most communities don't have.
• Introduce climate intervention (slides 10–12) as a third category alongside mitigation and adaptation, split into carbon dioxide removal (CDR) and solar radiation modification (SRM), with SAI framed as “global” and MCB/CCT framed as “local.”
• Discussion: (Ask after slide 8) Even if the world completely stopped emitting greenhouse gases today, the chart shows temperatures would take thousands of years to fully cool back down. Why does this “lag” matter for how urgently we act?
• Discussion: (Ask after slide 12) Climate intervention is split into CDR and SRM approaches. Why might SAI be described as “global” while MCB and CCT are described as “local”?

3. How Do Solar Radiation Modification Methods Work? (Slides 13–19)

• Present CDR via direct air capture (slide 13), then the three SRM methods: MCB (slide 14, brightening marine clouds with sea salt aerosol), CCT (slide 15, thinning high cirrus clouds to release more heat), and SAI (slides 16–17, inspired by volcanic eruptions and the “napkin diagram” combining mitigation, CDR, and SRM).
• Show the practical scale of SAI (slide 18: cost, aircraft, and sulfur needed to cool Earth 1ºC) and how the latitude of injection changes its regional effects (slide 19).
• Discussion: (Ask after slide 16) SAI is inspired by large volcanic eruptions that cool the planet for a few years. Why might scientists see this as reassuring evidence, and what might still be different between a natural eruption and a deliberately engineered injection?
• Discussion: (Ask after slide 19) The latitude where SAI is injected changes the pattern of cooling around the world. Why might choosing an injection strategy be as much a policy decision as it is a scientific one?

4. Weighing the Benefits and Risks of SRM (Slides 20–34)

• Present SAI's effectiveness/safety trade-offs (slide 20) and its researched benefits (slides 21–32): reduced extreme heat, marine heatwaves, and cyclone intensity, slower sea level rise, and partial recovery of monsoon timing — while noting that SRM cooling and mitigation cooling produce different rainfall patterns even at the same temperature.
• Present SRM's risks (slide 33: cannot undo all CO₂ effects, delayed ozone recovery, unknowns in agriculture/ecosystems/health) and termination shock (slide 34: rapid “catch-up” warming if SAI is suddenly stopped).
• Discussion: (Ask after slide 21) Researchers found SAI could reduce extreme heat, marine heatwaves, and cyclone intensity — but the slide says this is true only “if done prudently.” Why is that qualifier important?
• Discussion: (Ask after slide 32) Even in a world where SAI successfully controls the global temperature, rainfall patterns would look different from a world that reached the same temperature by cutting emissions. Why might “same temperature, different rainfall” be a difficult idea to communicate to the public?
• Discussion: (Ask after slide 34) Termination shock means that if SAI were suddenly stopped, warming would rapidly “catch up” to where it would have been anyway. What kinds of events might cause a country or program to suddenly stop SAI, and why does that make planning for this risk so important?

5. Governance: Who Decides, and Who Is Affected? (Slides 35–42)

• Present the Global North/South governance questions (slide 35) and the legal gray zones around territorial sovereignty, airspace, and international waters (slides 36–37), where no single treaty fully covers SRM.
• Discuss the current lack of international law regulating SRM (slide 38), the case of Brazil's own effort to get its government to formally discuss SRM (slides 39–40), and how local scientists and media can raise public awareness (slide 41), before closing with the Take Home Message (slide 42).
• Discussion: (Ask after slide 35) If SRM could benefit countries in the Global North while causing negative impacts in the Global South, who do you think should have the final say in whether it's deployed?
• Discussion: (Ask after slide 37) The governance-gaps diagram shows several international agreements that almost cover SRM but don't quite apply. Why is it risky for a powerful new technology to exist in a legal “gray zone” like this?
• Discussion: (Ask after slide 39) The lecture notes SRM wasn't even discussed at COP30 because many countries are unaware of it or focused on short-term measures. What are the risks of a technology this significant staying outside major international climate negotiations?

Conclusion

Close with a values-based question: Given the benefits, risks, and governance gaps covered in this lecture, do you think the world is ready to make decisions about SRM? What would need to happen first, and who should be part of that decision?

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

Before the temperature record, have students find a recent record-warm year, drought or flood where they live, and connect it to the global records and the slides on water security.

Bring in other perspectives

The lecture contrasts the Global North and the Global South. When discussing who should decide about SRM, ask groups to speak for a country that emits little but faces large impacts, and for a high-emitting country.

Share beyond the classroom

Students can prepare questions about SRM for a local decision maker or a visiting scientist, and share their answers to the closing question with another class.

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: This PDF was exported from Google Slides without tags, so screen readers can't follow its structure or read its slides in order. Remediate it (for example in Equidox) before publishing the file.

  • Download PDF: Lesson slides

• Role-play version: lesson slides

  Needs review: This PDF was exported from Google Slides without tags, so screen readers can't follow its structure or read it in order. Remediate it (for example in Equidox) before publishing the file.

  Slides for the “Shorter version with a science–policy role-play” version below.

  • Download PDF: Role-play version: lesson slides

• Stratospheric Aerosol Injection

  How SAI works and the volcanic analogy.

  • Open Link: Stratospheric Aerosol Injection

• What Is Termination Shock?

  A plain-language explainer on the risk raised in slide 34.

  • Open Link: What Is Termination Shock?

• UNEP (2023), One Atmosphere: An Independent Expert Review on Solar Radiation Modification Research and Deployment

  The report quoted on slide 10.

  • Open Link: UNEP (2023), One Atmosphere: An Independent Expert Review on Solar Radiation Modification Research and Deployment

• Copernicus: 2025 Was the Third-Hottest Year on Record

  The source for the temperature records on slide 4.

  • Open Link: Copernicus: 2025 Was the Third-Hottest Year on Record

• UN News: World Enters Era of ‘Global Water Bankruptcy’

  The UN report cited on slides 6–7.

  • Open Link: UN News: World Enters Era of ‘Global Water Bankruptcy’

• Degrees Initiative

  The organization funding SRM researchers in the Global South, mentioned on slide 39.

  • Open Link: Degrees Initiative

• Solar radiation modification: policy briefing

  The Royal Society’s overview of SRM science and policy, listed in the slides’ references.

  • Open PDF: Solar radiation modification: policy briefing

• How Hard Is It to Dim the Sun?

  Columbia Climate School article on the practical limits of stratospheric aerosol injection, listed in the slides’ references.

  • Open Link: How Hard Is It to Dim the Sun?

• Simulating the Impacts of SAI Deployment

  Reflective’s discussion of how SAI deployment simulations are designed, listed in the slides’ references.

  • Open Link: Simulating the Impacts of SAI Deployment

Other ways to teach this lesson

Shorter version with a science–policy role-play

Needs review: This version was the separate lesson “Climate Intervention: Building Blocks for Science–Policy Dialogues”, drafted by Claude from the November 2025 slides, and merged here because it is an earlier version of the same talk. Confirm the merge, and the drafted text, with Michelle Simões Reboita.

Michelle Simões Reboita gave an earlier, shorter version of this talk in Paraguay in November 2025, for a science–policy audience. It covers the same ground in fewer slides and ends with a role-play in which “decision-makers” put real questions about solar radiation modification to “scientists”. Use the “Role-play version: lesson slides” in Lesson materials; the slide numbers below refer to them.

Objectives

By participating fully in this activity, students will learn how to:

• Explain how burning fossil fuels since the Industrial Revolution has strengthened the greenhouse effect and warmed Earth by about 1.6°C
• Describe the Paris Agreement’s temperature goals and the three ways to respond to climate change: mitigation, adaptation, and climate intervention
• Explain how marine cloud brightening, cirrus cloud thinning, and stratospheric aerosol injection would each cool the planet, and what the scale of an SAI program would be
• Weigh SRM’s potential benefits against its environmental risks and unresolved governance challenges
• Communicate the science of SRM clearly in response to questions that decision-makers commonly ask

Lesson plan introduction

Because decisions about solar radiation modification would reach far beyond the laboratory, this lesson builds the scientific foundation students need to discuss SRM and then asks them to practice the kind of science–policy dialogue that researchers and governments are beginning to hold.

Activity details

1. The Physics of Climate Change (Slides 2–9)

• Present the lesson outline (slide 2), then trace how the Industrial Revolution began the large-scale burning of coal (slide 3).
• Compare Earth with the natural greenhouse effect (a mean temperature of about 13.5°C in 1850–1900) and with the human contribution (about 15.1°C in 2024, an increase of 1.6°C) (slides 4–5).
• Present recent temperature records (slides 6–7) and the projection that current policies lead to about 3.1°C of warming this century (slide 8).
• Discussion question: Why does the temperature keep rising even when emissions stop growing?

2. Consequences and the Paris Agreement (Slides 10–13)

• Show how higher greenhouse gas concentrations disturb the climate system, with examples such as the 2023 Amazon drought and the May 2024 floods in Porto Alegre, Brazil (slides 10–12).
• Present the Paris Agreement’s goals and the emissions cuts needed to meet them, and note that the greenhouse effect would persist even if emissions stopped today (slide 13).
• Discussion question: Which climate impacts have affected your own region, and how did people respond?

3. Ways to Respond and How SRM Would Work (Slides 14–20)

• Introduce the three responses: mitigation, adaptation, and climate intervention (slides 14–16), including UNEP’s conclusion that SRM is the only option that could cool the planet within years.
• Explain marine cloud brightening (slide 17), inspired by ship tracks; cirrus cloud thinning (slide 18), which targets outgoing infrared radiation rather than sunlight; and stratospheric aerosol injection (slide 19), inspired by large volcanic eruptions.
• Discuss the scale of SAI (slide 20): roughly 100–200 modified aircraft and about 10 Mt of sulfur dioxide a year, at a direct cost of about $10–20 billion a year, to cool Earth by 1°C.
• Discussion question: Why might SAI’s low direct cost make governing it harder rather than easier?

4. Benefits, Risks, and Challenges (Slides 21–24)

• Weigh the potential benefits of prudent SAI (slide 21), such as lower temperatures, fewer extreme heat events, and slower sea level rise, against the risks (slide 22), including delayed ozone recovery and major unknowns for agriculture, ecosystems, and health.
• Discuss the governance challenges (slides 23–24): no international law regulates SRM, so who would decide whether and how to use it?
• Discussion question: Who should have a say in decisions about SRM, and how should those decisions be made?

5. Role-Play: A Science–Policy Dialogue (Slides 25–26)

• Divide the class into “decision-makers” and “scientists.” Decision-makers choose questions from slide 25, which lists the questions that decision-makers most often ask about SRM, such as “Does it work?” and “What if it doesn’t work, or causes harm?”
• Scientists answer using evidence from the lesson, and say clearly when the honest answer is “we don’t know yet.”
• Close with the final message (slide 26): SRM needs the right governance, built by scientists and governments together.

Conclusion

Close with a values-based question: After the role-play, what did the “decision-makers” most need from the “scientists” to make a responsible choice? What should happen before anyone decides whether to use SRM?

Related lessons

• Introduction to the Climate System: teach first if your students are new to climate science: the same author's introduction to how the climate system works
• Solar Climate Intervention: Weighing Benefits, Risks, and Moral Hazard: another introduction to solar radiation modification, built around benefits, risks and moral hazard, with a graduate version on aerosol physics
• 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 Adaptation and Intervention: Wildfire Resilience and Solar Radiation Management: another introduction to solar radiation modification, framed around adapting to growing wildfire risk

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