Exploring Stratospheric Aerosol Injection as a Climate Solution

The world is experiencing rapid warming, with 2024 marking the first full year exceeding 1.5°C above the 19th-century average. Despite ongoing efforts, emissions continue to rise, with fossil fuel consumption projected to reach unprecedented levels in 2025. Current carbon removal technologies are insufficient, capturing only tens of thousands of tonnes annually compared to the estimated 5-10 billion tonnes needed. As the climate crisis intensifies, the exploration of innovative solutions, such as reflecting sunlight to mitigate warming, has gained attention.

The Guardian

Stratospheric aerosol injection (SAI) emerged from natural experiments, notably the 1991 eruption of Mount Pinatubo, which released approximately 15 million tonnes of sulfur dioxide (SO2) into the stratosphere, resulting in a temporary cooling of about 0.5°C. Research indicates that SAI could potentially offset 1°C of warming with an annual injection of around 12 million tonnes of SO2. However, experts emphasize that SAI should not replace emissions reductions; rather, it requires careful study to assess its feasibility and safety.

The Guardian

Critics argue against researching SAI due to potential misuse. However, proponents advocate for open and rigorous research to evaluate whether a well-governed approach could mitigate harm, particularly for vulnerable populations. Drawing parallels to medical research, a phased clinical trial model is proposed for SAI, beginning with small-scale experiments to understand aerosol behavior in the stratosphere. Initial phases would involve releasing minimal amounts of SO2 to gather data on aerosol formation and dispersion, which are critical for refining climate models.

The Guardian

The proposed research framework includes several phases. Phase one would involve releasing approximately 10 tonnes of SO2 to study its effects without significant climate impact. Subsequent phases could increase the scale of experiments, allowing researchers to observe how aerosols interact with atmospheric conditions. This structured approach aims to build confidence in the scientific understanding of SAI and ensure that any future deployment is based on empirical evidence.

The Guardian

As research progresses, the potential for a decision on SAI deployment will arise. If governments express interest, a phase three could involve controlled cooling efforts, aiming for a gradual reduction of about 0.1°C over five years, under strict observation and governance. This method contrasts with unregulated deployment, emphasizing the need for robust oversight mechanisms to ensure responsible decision-making.

The Guardian

The UK’s Advanced Research and Invention Agency (Aria) is seen as a crucial step toward advancing SAI research. Initiatives like those at Reflective aim to foster open science and public accountability in this field. The urgency of climate change necessitates proactive exploration of all potential solutions, including SAI. Waiting too long to investigate these options could hinder effective responses to the climate crisis.

The Guardian

• “But if it does, the only way to make a future responsible decision about its use will be to generate real-world evidence, transparently, before a crisis forces our hand.” — Author, Reflective

The Guardian

• “It’s how we make sure that any future decision – whether to move forward, reject the idea entirely or refine it – is based on facts, not fear or wishful thinking.” — Author, Reflective

The Guardian

• “Careful, open research can clarify whether a well-governed approach could reduce harm, particularly for the most vulnerable.” — Author, Reflective

The Guardian

• “The real danger isn’t asking the question.” — Author, Reflective

The Guardian