Stratospheric Aerosol Injection: The Secret Weapon to Fight Global Warming

Stratospheric Aerosol Injection: The Secret Weapon to Fight Global Warming

Climate change is an undeniable reality. Its current impacts on the environment are extensive, ranging from rising sea levels to more frequent extreme weather events. These effects will only worsen over time if left unchecked, leading to devastating consequences for our planet and future generations.

In this article, you will learn about how mimicking the cooling effect of stratovolcano eruptions can reverse global warming and give humanity more time to transition off fossil fuels and scale up carbon removal all without hindering growth. And some of the efforts that are underway to bring more attention to a critical tool we might need to use if we can’t stop heating up the Earth with greenhouse gases.

The Need for Immediate Action

Addressing climate change requires immediate action from all sectors of society to avoid a 2.7°F (1.5°C) temperature rise within a decade. Deep lifestyle changes and less reliance on fossil fuels are needed - a tough task for many countries, organizations, and individuals. While renewable energy, carbon dioxide removal, and reforestation hold promise, it will still take time we don't have and millions will suffer as we wait.

What is Stratospheric Aerosol Injection (SAI)?

Stratospheric aerosol injection (SAI) is a geoengineering technique designed to reduce global temperatures by introducing aerosols into the Earth's stratosphere. These aerosols reflect a portion of incoming sunlight back into space, resulting in a cooling effect on the planet's surface. The most researched and naturally occurring aerosol is sulfur dioxide (SO2).

How It Works

Mimicking Natural Processes

SAI is inspired by natural processes, such as the cooling effect observed after large volcanic eruptions. When volcanoes release sulfur dioxide into the atmosphere, it reacts with water vapor to form sulphate aerosols, which then reflect sunlight and lower global temperatures. One such eruption happened in 1991 when Mount Pinatubo eruption injected 20 million tons of sulfur dioxide into the stratosphere and temporarily cooled the Earth by 0.5C for over a year.

Cooling the Earth's Surface

The primary goal of SAI is to mimic this natural cooling effect by artificially introducing sulphate aerosols into the stratosphere. By reflecting a portion of incoming sunlight, these aerosols help to cool the Earth's surface and potentially slow the effects of climate change. Think sunscreen spray for Earth like sunscreen spray for your skin. When applied correctly, it prevents sunburn.

The History of SAI Research

Previous Studies and Experiments

Research into SAI has been ongoing for several decades. Early studies focused on understanding the potential impacts of aerosol injection on the atmosphere and global temperatures. However, it was not until the 21st century that more advanced experiments and simulations were conducted to determine the feasibility and effectiveness of this approach.

Recent efforts

Today, SAI research has progressed, with numerous studies and experiments exploring various aspects of the technique. Examples of recent efforts include the Stratospheric Controlled Perturbation Experiment (SCoPEx) led by Harvard University, which aimed to better understand the risks and benefits of SAI by conducting small-scale experiments in the stratosphere. This inspired the work of Make Sunsets, a company actively deploying SAI technology using high-altitude balloons. This includes advances in aerosol injection methods, improved climate modeling, and a better understanding of the potential risks and benefits associated with SAI implementation. For example, Dr. Ken Calderia recently presented modeling done by United Nations Environment Programme (2023). One Atmosphere: An independent expert review on Solar Radiation Modification research and deployment. In one of his slides, he said, "Model results indicate that solar geoengineering could offset most climate change for most people most of the time."

 United Nations Environment Programme (2023). One Atmosphere: An independent expert review on Solar Radiation Modification research and deployment.

The Science Behind SAI

The Role of Aerosols in the Atmosphere

The Difference Between Tropospheric and Stratospheric Aerosols

Aerosols are tiny particles suspended in the Earth's atmosphere. They can be found in both the troposphere, which extends from the Earth's surface up to about 8-15 kilometers, and the stratosphere, located above the troposphere up to about 50 kilometers. Make Sunsets deploys aerosols 20 kilometers and above. While tropospheric aerosols have a relatively short lifespan and can impact local weather and air quality, stratospheric sulfate aerosols are more stable and have global consequences.

The Process of SAI

Injecting Aerosols into the Stratosphere

SAI aims to artificially replicate the cooling effect of natural sulfate aerosols by injecting them into the stratosphere. Various delivery methods have been proposed, such as using high-altitude balloons, aircraft, or even specialized rockets. Due to current demand of SAI as a service and funding, Make Sunsets uses high-altitude balloons in various sizes. One balloon can offset the warming effect of 1,000 tons of carbon dioxide for a year, as demand increases, we have high-altitude balloons that can offset the warming effect of 100,000 tons of CO2 for a year. That’s approximately 4.6 million mature trees that live for a year.

The Formation of Sulfate Aerosols and Their Effects

Once formed, sulfate aerosols can remain in the stratosphere for up to a few years, continuously reflecting sunlight and providing a cooling effect. The magnitude and duration of this cooling effect depend on the amount of aerosols injected, their size, and their distribution in the stratosphere.

Potential Benefits of SAI

Reducing Global Temperatures

By reflecting sunlight, SAI has the potential to significantly reduce global temperatures, providing a temporary solution to help mitigate the impacts of climate change as we transition to a more sustainable future.

Mitigating Extreme Weather Events

SAI could also help to reduce the frequency and intensity of extreme weather events, such as heatwaves, droughts, and storms, which are exacerbated by climate change.

Improving Agricultural Yields

As a result of reduced temperatures and more favorable growing conditions, SAI implementation could lead to improved agricultural yields, supporting food security and global economies. Preliminary modeling a ~10% net increase in crop yield.

Challenges and Concerns of SAI: Opportunities for Improvement

Technological Hurdles

Delivery Methods

One of the primary challenges of SAI is developing efficient and cost-effective methods for injecting sulphate aerosols into the stratosphere. While various delivery systems have been proposed, such as high-altitude balloons, aircraft, and specialized rockets, further research and development will help determine the most viable options and create innovative solutions.

Monitoring and Measuring the Impacts

Another challenge that presents an opportunity for growth is monitoring and measuring the impacts of SAI on the Earth's climate and ecosystems. Developing sophisticated tools and models will help accurately predict and assess the effects of aerosol injection on global temperatures, weather patterns, and other environmental factors. As demand scales, we will develop these tools, but currently rely on the work of Dr. David Keith to quantify our impact.

Environmental Risks

Ozone Depletion

One potential environmental risk associated with SAI is ozone depletion. However, as we continue to research and develop this technology, we will find ways to mitigate or even eliminate this risk, ensuring that SAI implementation does not exacerbate existing ozone layer depletion. And Dr. David W. Fahey, Director of the National Oceanic and Atmospheric Administration’s Chemical Sciences Laboratory revealed that studies show sulfur aerosols from stratospheric aerosol injection could impact the ozone layer, but not catastrophically. The 1991 Mount Pinatubo volcanic eruption demonstrated the ozone layer's resilience after temporarily cooling the planet by 0.5°C. Despite uncertainties, these findings suggest geoengineering methods like SAI could be explored without causing irreversible damage to the ozone layer. (Source: The New York Times)

Impacts on Weather Patterns

SAI may also have unforeseen consequences on regional and global weather patterns. With continued research and development, we can better understand these potential impacts and develop strategies to avoid negative effects, ensuring that SAI contributes positively to climate change mitigation.

Addressing the Moral Hazard Argument: The Reality of Energy Sources and Costs

The “moral hazard” argument against the implementation of geoengineering technologies like SAI raises the concern that relying on these technologies could diminish the urgency to reduce greenhouse gas emissions and transition towards sustainable energy systems. However, to fully appreciate the complexity and reality of this argument, we must consider the present state of energy sources and their costs.

As of today, fossil fuels - coal, natural gas, and oil - continue to represent a significant proportion of the global energy mix, primarily because they are more readily available and less expensive than many alternatives. This economic reality often undermines the transition towards renewable energy, particularly in developing nations where access to affordable energy is a critical factor in economic development and poverty reduction.

The reality of energy cost and availability shapes the moral hazard argument in a unique way. Instead of assuming that the deployment of SAI or similar technologies would lead to complacency in our fight against climate change, it's more realistic to perceive them as temporary measures that can buy us time while we strive to make renewable energy sources more accessible and cost-effective.

In this context, it is crucial to underscore that the transition to a low-carbon economy will require not only advancements in technology but also comprehensive policy support, increased investments in clean energy research and infrastructure, and the implementation of economic incentives to make renewable energy sources more competitive.

This, however, does not mean that we can postpone immediate action. It is essential to continue with mitigation efforts, such as increasing energy efficiency, promoting sustainable land use practices, and reducing carbon-intensive practices across various sectors. The deployment of geoengineering technologies should not be seen as a replacement for these efforts but as a supplementary tool in our broader climate action toolkit.

In conclusion, while the moral hazard argument presents a valid concern, the current economic realities of energy cost and availability indicate that the argument may be unrealistic. The use of SAI and similar technologies may, therefore, serve as a valuable part of an integrated approach to climate change mitigation - an approach that must also include persistent efforts to transition towards more accessible and cost-effective renewable energy systems.

Current SAI Research and Development

Ongoing Experiments and Studies

SCoPEx Project

One prominent example of SAI research was the Stratospheric Controlled Perturbation Experiment (SCoPEx), led by Harvard University. This project aimed to better understand the risks and benefits of SAI by conducting small-scale experiments in the stratosphere, using a high-altitude balloon to release a controlled amount of aerosols and then measure their impacts on the atmosphere. Unfortunately, SCoPEx has failed and is no longer ongoing.

Make Sunsets: The Only Company Deploying SAI

As of now, Make Sunsets is the only company actively deploying stratospheric aerosol injection (SAI) technology. The company uses high-altitude balloons to release aerosols 20 kilometers and above, helping to offset the warming effect of greenhouse gases and mitigate the impacts of climate change.

Technological Advancements

New Delivery Methods

As SAI research progresses, new and improved delivery methods are being developed to more efficiently and safely introduce aerosols into the stratosphere. Make Sunsets currently uses high-altitude balloons in various sizes, with future capabilities of offsetting the warming effect of up to 100,000 tons of CO2 for a year.

Improved Monitoring Tools

Another area of advancement is the development of better monitoring tools and techniques to accurately measure the impacts of SAI on the Earth's climate and ecosystems. This includes the use of satellites, ground-based sensors, and advanced modeling techniques to track and predict the effects of aerosol injection on global temperatures, weather patterns, and other environmental factors.

Policy Discussions and International Collaborations

The Role of Governments and Organizations

As SAI research continues to advance, governments and organizations are increasingly recognizing the potential implications of this technology. This has led to policy discussions and international collaborations to establish guidelines, regulations, and agreements for the responsible development and deployment of SAI and a call for more research. The White House Office of Science and Technology Policy (OSTP) is releasing a report in response to a Congressional mandate in the Consolidated Appropriations Act 2022 related to solar radiation management, also known as solar geoengineering.

The Importance of Collaboration in SAI Development

The Role of the Public and Private Sectors

Funding and Support for SAI Initiatives

Both the public and private sectors have a crucial role to play in supporting SAI research and development. Government funding, private investment, and partnerships between academia and industry are all essential for advancing our understanding of SAI and facilitating its responsible implementation.

Public Awareness and Education

Engaging the public and raising awareness about SAI is also critical. By educating people about the potential benefits and risks of aerosol injection, we can foster informed discussions, build public support, and ensure that any decisions made about SAI implementation are based on a solid understanding of the underlying science and its potential consequences. For example, the Make Sunsets team gave out balloons filled with chalk dust and helium in a park to educate people on SAI.

Inviting the Audience to Join the Journey

Purchasing Cooling Credits

One way that individuals can support SAI research and development is by purchasing cooling credits from organizations like Make Sunsets. These credits help fund ongoing SAI projects and contribute to the broader effort to mitigate the impacts of climate change.

Signing up for the Newsletter

Staying informed about the latest SAI developments is also essential. By signing up for our newsletter, individuals can keep up to date on the latest research, innovations, and policy discussions related to SAI.

Partnering with Make Sunsets

Lastly, partnering with organizations like MakeSunsets can help to advance SAI research and implementation. By working together, we can pool resources, knowledge, and expertise, ultimately contributing to the development of effective and responsible solutions for combating climate change.

Final Thoughts

Stratospheric aerosol injection (SAI) holds significant promise as a potential solution to help combat climate change. By artificially introducing aerosols into the stratosphere, SAI can temporarily reduce global temperatures and slow the impacts of climate change, providing a crucial buffer as we transition to a more sustainable future. SAI is temporary, inexpensive, and scaleable stop gap solution.

The Urgency of Addressing Climate Change

As the devastating effects of climate change become increasingly apparent, the need for immediate action has never been more urgent. SAI is just one of many potential strategies to help mitigate these impacts, and its development and implementation must be considered as part of a broader, multifaceted approach to addressing this global crisis.

The Call to Action for Readers to Join the Efforts and Stay Informed

Join us in our mission to combat climate change and support SAI research and development. Stay informed about the latest advancements by signing up for our newsletter, consider purchasing cooling credits to help fund ongoing projects, or partner with us to pool resources and expertise. Together, we can work towards a cooler, more sustainable future for our planet.

Author's note: 80% of this blog post and title was written using the help of ChatGPT and the hero image was generated using DreamStudio. The title was generated based off the content of the blog post. This blog was originally written on 12/2/2022.

Back to blog


This article was incredibly helpful! Thank you for publishing it. Huge fan of the work y’all are doing at Make Sunsets too!

Nate Matherson

This year in France, for the 2d year in a row, we celebrated X mas with shirts and beach shorts, instead of scarves and gloves. Reading your blog gave me hope and faith in humanity. And a dream : get back to pre industrial temperatures, get back to the real world.

A from France

Andrew – Thank you for – history will remember you.
I saw on your FAQs that you have agreed to debate if there’s an audience of 200 or more. I totally want to be there in the audience to root you on. i assume that’s the type of content we can expect from your youtube channel (just subscribed)

but homie – if i had a dime for every cease and desist letter you’re going to get….

Some of the letters will be worse no doubt and I hope my supportive comment balances those out. Get a good lawyer and stay strong brother.

kevin s. thompson - austin, tx

Leave a comment

Please note, comments need to be approved before they are published.