Can Stratospheric Aerosol Injection Refreeze the Arctic?

Overview

Objectives

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

• Explain why solar geoengineering (SAI, marine cloud brightening, cirrus cloud thinning) is being studied as a possible addition to emissions cuts and carbon dioxide removal, and why its cooling effect would only be temporary if stopped
• Describe how climate models and the Mount Pinatubo eruption both point to stratospheric aerosols cooling the planet, and identify major sources of scientific uncertainty in these predictions
• Explain why the Arctic is warming faster than the rest of the planet, and why some scientists specifically study whether SAI could help preserve Arctic sea ice
• Evaluate the trade-offs of targeting SAI at the Arctic, including its effects beyond the Arctic itself (Northern Hemisphere cooling, shifts in tropical rainfall) and remaining ecological uncertainties

Grade Level

Grades 9-12, Undergraduate

Standards

These are Next Generation Science Standards (NGSS) performance expectations.

• HS-ESS3-5 — Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth systems.
• 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-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 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

United Nations Sustainable Development Goals

• SDG 13 — Climate Action: Take urgent action to combat climate change and its impacts
• SDG 14 — Life Below Water: Conserve and sustainably use the oceans, seas, and marine resources — including the sea ice, fisheries, and marine food webs

Materials Required

• PDF slideshow "Arctic_Momentum_(August_2023).pdf" (Can Stratospheric Aerosol Injection refreeze the Arctic?, A. Wells & M. Henry, University of Exeter)
• Paper and pencil
• This discussion guide, since the lecture slides do not include built-in discussion prompts

Learning Sequence

Lesson Plan Introduction

As the Arctic warms faster than the rest of the planet, this lesson examines whether Stratospheric Aerosol Injection could help refreeze it, and asks students to weigh the science, the modeling uncertainty, and the limits of treating any geoengineering intervention as purely “local.”

Activity Details

1. Why Study Solar Geoengineering? (Slides 2–9)

• Introduce the three leading solar geoengineering methods (slides 2–3): stratospheric aerosol injection (SAI), cirrus cloud thinning, and marine cloud brightening.
• Build up the emissions/impacts framework (slides 4–9): even aggressive emissions cuts leave climate impacts elevated for a long time, melting glaciers and rising seas continue past net-zero, and carbon dioxide removal (“Plan A”) combined with solar geoengineering (“Plan A+”) could shave the peak in climate impacts.
• Discussion: (Ask after slide 7) Why do melting glaciers, ice sheets, and rising sea levels keep getting worse even after the world reaches net-zero emissions?
• Discussion: (Ask after slide 9) What's the difference between “Plan A” (cutting emissions plus carbon dioxide removal) and “Plan A+” (adding solar geoengineering on top)? Why might someone want the “+”?

2. The Basics of Stratospheric Aerosol Injection (Slides 10–23)

• Present the volcanic analogy (slides 10–15): the 1991 Mount Pinatubo eruption naturally injected sulfur dioxide into the stratosphere, which formed reflective aerosols and cooled the planet for about a year before falling back out.
• Walk through the basic SAI process (slides 19–21) and its potential benefits (slide 22): continuous SO₂ injection forms an aerosol cloud that reflects sunlight, potentially reducing heat waves, floods, droughts, sea ice melting, sea level rise, and fire risk.
• Present the uncertainties involved (slide 23), split into modeling uncertainties (which scenario, target, model, and injection strategy is used) and physical uncertainties (uneven surface cooling, precipitation changes, ozone depletion, and more).
• Discussion: (Ask after slide 15) What does the Pinatubo eruption teach us about how long SAI's cooling effect would last if injections were stopped?
• Discussion: (Ask after slide 23) Looking at the modeling and physical uncertainties listed, which one do you think would be hardest for scientists to reduce, and why?

3. Why the Arctic Warms Faster — and Why That Matters (Slides 31–32)

• Present Arctic amplification (slide 31): the Arctic has been warming roughly two to four times faster than the global average since the 1990s.
• Discuss the role of sea ice decline (slide 32): as reflective sea ice melts, it exposes darker ocean water that absorbs more sunlight, which is thought to be a major driver of this faster warming.
• Discussion: (Ask after slide 32) Why might a region that's already warming and losing sea ice faster than the rest of the planet be an especially important place to study solar geoengineering?

4. Could SAI Specifically Cool the Arctic? (Slides 33–38)

• Show that two independent climate models agree SAI would cool the Arctic more than the rest of the planet, even without specifically targeting it (slides 33–35).
• Present Arctic-focused injection strategies (slides 36–38): by injecting SO₂ at 60°N each spring, models show Arctic sea ice could be maintained at 2030 levels or even restored to 2010 levels.
• Discussion: (Ask after slide 35) Two different climate models were shown cooling the Arctic under SAI. Why might it matter that both models agree on the direction of this effect, even if they disagree on the exact amount?
• Discussion: (Ask after slide 38) If scientists can adjust where aerosols are injected to specifically target Arctic sea ice recovery, what questions would you want answered before this was ever attempted in the real world?

5. The Limits of “Local” Arctic Geoengineering (Slides 39–46)

• Present the key caveat (slides 39–40): Arctic-focused SAI would still cool the entire Northern Hemisphere and shift the tropical rainbelt — it is not a “local” intervention.
• Show the range of ecological uncertainties involved (slide 44): changes to species distributions, biodiversity hotspots, migrations, and fisheries, spanning both land and ocean ecosystems.
• Summarize the conclusions (slides 41–43, 45–46): climate models and natural analogs suggest SAI would cool the planet and could be focused on the Arctic, but deep uncertainties remain, and researchers report it can be difficult to get funding and support for this work.
• Discussion: (Ask after slide 40) Even if the goal is to cool just the Arctic, this research shows the whole Northern Hemisphere would cool and the tropical rainbelt could shift. Who do you think should have a say in that decision, given that they never asked for the intervention?
• Discussion: (Ask after slide 44) Looking at the diagram of ecological uncertainties, which potential impact worries you most, and why?
• Discussion: (Ask after slide 46) What would you want to know about SAI's effects on ecosystems and local communities before supporting even small-scale field testing?

Conclusion

Close with a values-based question: Given the deep uncertainties around SAI's regional and ecological effects, do you think research into Arctic-focused SAI should continue? What conditions, if any, would need to be met before even small-scale field testing should be allowed?

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 slides on Arctic warming, ask students how the Arctic is connected to their own place, through sea level, weather, fisheries, shipping or migrating animals.

Bring in other perspectives

Bring in the views of Arctic Indigenous peoples and of countries whose monsoon rainfall could change, using the reading on SAI and the monsoons, so students weigh who would benefit from a regional intervention and who would bear its risks.

Share beyond the classroom

Students can turn their answer to the closing question into a short statement for a youth climate assembly or a school newsletter, explaining whether research into Arctic-focused SAI should continue.

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

• Stratospheric Aerosol Injection

  How SAI works, the Pinatubo analogy, and the stratosphere’s role.

  • Open Link: Stratospheric Aerosol Injection

• NASEM (2021), Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance

  Background on the broader scientific and governance context for SAI research.

  • Open Link: NASEM (2021), Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance

• Lee et al. (2023), High-Latitude Stratospheric Aerosol Injection to Preserve the Arctic

  The peer-reviewed study behind the Arctic-focused injection results shown in slides 36–40.

  • Open Link: Lee et al. (2023), High-Latitude Stratospheric Aerosol Injection to Preserve the Arctic

• NOAA Arctic Report Card

  Annual updates on Arctic amplification, sea ice, and related Arctic climate indicators.

  • Open Link: NOAA Arctic Report Card

• What do climate models say about the impact of Stratospheric Aerosol Injection on the monsoons?

  Background reading: Matthew Henry's short post on why aerosols injected in one hemisphere or at the equator could disrupt monsoon rainfall, including the Lee et al. (2023) study behind this lesson's Arctic results.

  • Open Link: What do climate models say about the impact of Stratospheric Aerosol Injection on the monsoons?

Related lessons

• Modeling the Potential Impacts of Stratospheric Aerosol Injection: Knowns & Unknowns: how climate models simulate stratospheric aerosol injection, why they disagree, and what research is still needed
• Introduction to Marine Cloud Brightening: a different technique, marine cloud brightening, including whether it could protect Arctic sea ice

Credit and contact