Stratospheric Aerosol Injection

The idea

Stratospheric Aerosol Injection, also known as SAI, is one of the most widely discussed and studied climate cooling method with research almost exclusively limited to computer modelling. It aims to reflect a portion of the Sun’s energy back into space by dispersing tiny reflective particles into the upper atmosphere. This idea is inspired by natural volcanic eruptions, which have been observed to cool the Earth for short periods.

SAI involves releasing fine particles into the stratosphere, a part of the atmosphere about 10 – 50 kilometres above the Earth’s surface.

Once dispersed, the particles would reflect incoming solar radiation back into space, which would reduce the amount of solar energy reaching this Earth’s surface, and in turn lowering global temperatures temporarily.

This cooling effect is similar to what occured after volcanic eruptions such as the 1991 eruption of Mount Pinatubo, which led to a global temperature drop of about 0.5^oC the following year.

CCR's research effort in Cambridge’s Department of Geography focuses on establishing paleoclimate records, and investigating the Atlantic Meridional Overturning Circulation, as well as where large cluster volcanoes may have had an impact on the climate.

The SAIM project

Novel Materials for Stratospheric Aerosol Injection

Prof Hugh Hunt is leading a project on Natural Materials for Stratospheric Aerosol Injection, in collaboration with Harvard University and Imperial College London, and supported by the Advanced Research + Invention Agency (Aria).

Stratospheric Aerosol Injection (SAI) is an increasingly discussed potential climate cooling method, but the most commonly proposed materials (based on sulfur) carry hazards in this context, including potential ozone depletion, toxicity, and altered atmospheric circulation patterns. Alternative, safer materials have been proposed for use in SAI, but little is currently understood about how they would behave in the stratosphere. This project will undertake fundamental research to investigate the properties and behaviour of non-toxic, non-sulfate materials for this purpose.

The research combines laboratory studies and computational modelling with highly controlled material exposure experiments. In these experiments, tiny (milligram) amounts of non-toxic materials (such as limestone, dolomite, and corundum) will be placed inside a specialised container. This container will be transported to the stratosphere by a solar-powered high-altitude glider. This uncrewed vehicle is remotely piloted from the ground and capable of remaining aloft and in place for periods ranging from days to weeks. This method allows for precise flight control, far exceeding the capabilities of traditional high-altitude balloons.

The materials will be exposed within the stratosphere for periods ranging from hours to weeks. Crucially, the materials will remain entirely confined; nothing is released into the atmosphere. The glider is then piloted back to Earth and the samples are examined in a laboratory. Studying these materials will reveal how stratospheric conditions affect their properties over time. This foundational science is essential to advance our understanding of the potential impacts of SAI and to determine if any of these alternative materials warrant further study.

View the full grant agreement for this project, which outlines its objectives, milestones, and deliverables here.

An engagement plan is currently being prepared and will reviewed in due course by the ARIA Oversight Committee. Once reviewed, this will be published on our, and ARIA's, website.