Geoengineering atmosphere to reflect sun’s heat ‘no better than shot in the dark’, scientists warn

Research shows reductions in burning greenhouse gases, not attempts to reflect the sun, are the best way to mitigate the climate crisis, writes Harry Cockburn

Using particulates or aerosols to reflect some of the sun’s energy is no longer within the realm of science fiction, but its impacts could be unexpected and far reaching (Getty)

The cooling effect of large volcanic eruptions is well documented, with eruptions believed to be a major contributing factor behind natural phenomena such as the little ice age when temperatures began to drop by around a degree in Europe during the 1500s.

The particles ejected by the immense power of large eruptions hung in the atmosphere effectively shielding the surface of the Earth from the sun’s rays.

As the climate crisis worsens - nine of the hottest years in human history have occurred in the last decade - scientists are pondering whether using technology to reflect some of the sun’s energy could similarly but the brakes on runaway global warming.

However, the impacts of such geoengineering by humans are not well understood. As a result, scientists are now examining the potential consequences of reflecting some of the sun’s radiation away from the planet - a climate intervention known as solar radiation modification (SRM).

Every month since September 2019, the Climate Intervention Biology Working Group - a team of internationally recognised experts in climate science and ecology - has gathered remotely to explore whether such a project could be done and the huge number of ways it could impact life on our planet.

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They said that such geoengineering Earth’s atmosphere “is more than just a science-fiction scenario”.

Phoebe Zarnetske, associate professor at Michigan State University and co-leader of the group said: “There is a dearth of knowledge about the effects of climate intervention on ecology.”

“As scientists, we need to understand and predict the positive and negative effects it could have on the natural world, identify key knowledge gaps, and begin to predict what impacts it may have on terrestrial, marine, and freshwater species and ecosystems if it were adopted in the future.”

The costs and technology needed to reflect the sun’s heat back into space are currently more attainable than other climate intervention ideas like absorbing carbon dioxide (CO2) from the air, through methods such as carbon capture and storage (CCS) the team has said - many countries have pinned their hopes of reaching net zero on the availability of such technology in the near future.

The feasibility of planetary-wide SRM efforts hinge on accurate predictions of the various possible outcomes modelled by computer simulations run by the Geoengineering Model Intercomparison Project (GeoMIP).

A new paper authored by the group, published in the Proceedings of the National Academy of Sciences of the United States lays the foundation for expanding GeoMIP’s scope to include the incredible range and diversity of Earth’s ecosystems.

“While climate models have become quite advanced in predicting climate outcomes of various geoengineering scenarios, we have very little understanding of what the possible risks of these scenarios might be for species and natural systems,” said Jessica Gurevitch, distinguished professor in the Department of Ecology and Evolution at Stony Brook University.

“Are the risks for extinction, species community change, and the need for organisms to migrate to survive under SRM greater than those of climate change, or does SRM reduce the risks caused by climate change?” she said.

While the scientists acknowledged that humans could retain some level of control over the impacts, as theoretically, it would be possible to continuously replenish the cloud and control its thickness and location to achieve a desired target temperature, they also warned that the complexity of the world could lead to unexpected outcomes.

The team said their research “reveals the under-researched complexity of cascading relationships between ecosystem function and climate under different scenarios”.

As a result they argue that existing efforts to mitigate the worsening climate crisis must continue regardless of whether SRM is adopted, and the question remains whether some or any SRM can be beneficial in addition to decarbonisation efforts.

One of the main methods the researchers examined was stratospheric aerosol intervention (SAI), which would reduce some of the sun’s incoming radiation by reflecting sunlight back into space, similar to what happens after large volcanic eruptions.

“Although SAI may cool Earth’s surface to a global temperature target, the cooling may be unevenly distributed, affecting many ecosystem functions and biodiversity,” Dr Zarnetske said.

“Rainfall and surface ultraviolet radiation would change, and SAI would increase acid rain and would not mitigate ocean acidification.”

The researchers said as a result they believe SRM “is not a magic bullet for solving climate change”.

Until the working group’s efforts inspire new research into the effects of different climate intervention scenarios, the scientists said “SRM is more akin to a shot in the dark”.

“We hope that this paper will spark a lot more attention to this issue and greater cooperation between scientists in the fields of climate science and ecology,” said Professor Gurevitch.