Simons Foundation Funds 14 Projects Exploring Earth-Cooling Techniques as Part of New International Research Program

International efforts to reduce greenhouse gas emissions may not be enough to prevent the worst effects of climate change over the coming decades and meet the goals set by the 2015 Paris Agreement. Indeed, the rapid heating of the ocean over the past two years suggests that the Earth’s temperature may rise even faster than some models predict.

“This is an all-hands-on-deck moment,” says Simons Foundation president David Spergel. “We will likely need a wide set of tools to mitigate global warming. While reduction in carbon emissions will be essential, recent reports from the United Nations Environment Programme, the U.S. government, the European Commission and the U.S. National Academy of Sciences have recommended research on potential temporary interventions that could help cool the planet as nations reduce their carbon emissions and develop ways to remove existing carbon dioxide, methane and other greenhouse gases from the atmosphere. Our goal is to support the basic science needed to understand the risks and benefits of these potential interventions.”

With that goal in mind, the Simons Foundation and Simons Foundation International have launched a new collaborative research program to advance our scientific understanding of methods that aim to cool our planet by increasing the reflection of sunlight away from the atmosphere or by changing the properties of clouds. These solar radiation modification techniques could help temporarily limit climate change, but assessments of their safety and feasibility are inhibited by large uncertainties surrounding their effectiveness, longevity and environmental impact.

The 14 research projects funded by the new program will pursue basic research questions underlying these uncertainties, focusing specifically on two different solar radiation management approaches.

The first investigates particles, known as aerosols, that could be injected into the stratosphere to reflect sunlight away from Earth — an effect already seen in nature when volcanoes erupt, ejecting sulfate particles into the atmosphere.

The second approach explores modifying the properties of clouds. Several projects will investigate various methods of thinning wispy high-altitude cirrus clouds to allow more of the planet’s heat to escape into space. One project will focus on a different cloud type and evaluate the influence of pollution aerosols from the shipping industry on the reflectivity of low-lying clouds over the ocean.

“The properties of different types of aerosols are not well understood, leading to substantial uncertainty in how they would affect our climate on a global and regional scale,” says program consultant Emily Carter, a professor at Princeton University and associate laboratory director at the Department of Energy’s Princeton Plasma Physics Laboratory. “The fundamental measurements and modeling of such properties, supported by this international collaborative, are urgently needed to increase understanding before any such climate intervention strategy should ever be contemplated for large-scale deployment.”

The solar radiation management science program — funded by the Simons Foundation and Simons Foundation International and administered by the Simons Foundation — will provide up to $10 million per year over the next five years across all the projects.

Rajan Chakrabarty of Washington University in St. Louis and his team will investigate the optical properties of two prospective sunlight-reflecting aerosols — calcite and aluminum oxide — and produce a database of their findings that can be immediately implemented in new and existing climate models.

Zamin Kanji of ETH Zürich in Switzerland and his colleagues will use atmospheric chemistry, physics and materials chemistry to study the formation of ice crystals in the laboratory. Such crystals are involved in the formation of cirrus clouds, the thinning of which can help to mitigate climate warming.

Frank Keutsch of Harvard University and his team will lead an effort to identify alternatives to sulfuric acid for stratospheric aerosol injection. Sulfuric acid is the most well-studied candidate, but its introduction could produce negative impacts such as increased ozone depletion, acid rain and stratospheric warming. Alternative candidates may yield similar benefits with fewer unwanted side effects.

Jasper Kok of the University of California, Los Angeles, and his colleagues will model the impacts of winter cloud thinning in the high Arctic. The thinning of so-called ‘mixed-phase regime’ clouds could dissipate heat held near the surface and slow the melting of sea ice with fewer side effects than other solar radiation management techniques.

Ulrike Lohmann of ETH Zürich will similarly model mixed-phase regime cloud thinning. Because this form of thinning is more localized and operates over shorter timescales than stratospheric aerosol injections, new models are needed to properly assess its impact.

Beiping Luo of ETH Zürich and his team will model and experimentally study the atmospheric processes that act on particles involved in stratospheric aerosol injection, including new prospective candidates.

Faye McNeill of Columbia University will use an aerosol flow tube to investigate the breakdown products and kinetics of proposed stratospheric aerosol injection materials at stratospheric temperatures.

Romaric Odoulami of the University of Cape Town in South Africa will investigate potential alternative materials for use in stratospheric aerosol injection, including crushed diamonds, dust, calcite and other candidates. The project will also explore the simulated climate response for agriculture, biodiversity, energy and water resources across Africa.

Thomas Preston of McGill University in Canada and his team will use aerosol optical tweezers and electrodynamic traps to study individual aerosol particles, with a goal of exploring key microphysical properties under conditions relevant to stratospheric aerosol injection.

Timofei Sukhodolov of Physical Meteorological Observatory Davos / World Radiation Center in Switzerland will oversee an international team investigating the surface and bulk chemistry processes associated with alternative stratospheric aerosol injection candidates. This information will inform models on whether such aerosols have fewer side effects than traditional sulfates, including ozone depletion and lower stratospheric heating.

Simone Tilmes of the National Center for Atmospheric Research and her team will study the impacts of alternative stratospheric aerosol injection candidates on atmospheric composition, ozone degradation, ice cloud formation and climate feedbacks. Their findings will be integrated into existing models.

Gabriel Vecchi of Princeton University and his team will model a novel solar radiation management strategy that directly targets the greenhouse effect by changing temperatures in the stratosphere, and compare their results with traditional strategies such as stratospheric aerosol injection.

Paul Wennberg of the California Institute of Technology and his team will investigate the effects of recent legislation limiting sulfur emissions produced by international shipping. The group will track recent ship emissions using airborne observations and study the changing chemical composition of ship emissions to quantify the impact of these changes on global cloudiness and radiative forcing.

Robert Wood of the University of Washington and his colleagues will study how turbulence changes injected plumes over time. This information will strengthen existing models of plume evolution and strengthen estimates of both the cooling magnitude and the side effects of stratospheric aerosol injection.