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By Adam Vaughan

With activist Greta Thunberg and the Extinction Rebellion protestors leading the calls for urgent action on climate change, interest is turning once again to geoengineering. The Intergovernmental Panel on Climate Change has said that we cannot limit warming to 1.5°C without taking drastic action. Is it time to take a more serious look at the prospect of deliberately intervening in the world’s climate?

The University of Cambridge is looking to establish a “centre for climate repair”, led by former UK chief scientific adviser David King. One focus will be investigating “approaches that might be used to repair the damaged climate”, a group of methods usually known as geoengineering.

Emily Shuckburgh, who leads the University of Cambridge’s Carbon Neutral Futures Initiative, says there is spectrum of approaches to consider. “Some we would clearly not [as a society] want to do,” she says, pointing to any sort of geoengineering intervention that would disrupt weather patterns.

A different approach that has received intense interest in recent years is solar radiation management, or solar engineering. This could involve putting aerosols into the atmosphere to effectively create a giant sunshade for the Earth. A decade ago the Royal Society gave solar geonengineering a cautious welcome. The approach could, it said, have negative side-effects on weather systems, and would have to be continually maintained. However, the society’s report concluded that it warranted further investigation.

Research into solar radiation management mushroomed in the following years, with more than 500 papers published on solar geoengineering. One recent paper concluded the approach could effectively reduce warming without harmfully reducing rainfall patterns as a side-effect.

David Keith of Harvard University, a co-author of that study, says there is substantially more research into the technique taking place than in the past. Funding for solar geoengineering science is still relatively small though, at less than $10m a year globally. “The central question is should we get serious? Should we have an international, open access research programme?” he asks. His answer is “absolutely yes”.

A fool’s paradise?

So far, little solar geoengineering research has taken place out in the physical world. Keith is involved in a research project that would change that by using a high altitude balloon to put a kilogram of calcium carbonate in the stratosphere. The project has been in the works for five years already and has funding, but Keith would not be drawn on when it is likely to happen.

Other projects have failed to materialise. One UK-led scheme to spray water into the stratosphere was cancelled in 2012, due to a conflict of interest issue over a patent and concerns about the governance of geoengineering experiments.

Matthew Watson of the University of Bristol, who led that project, says we still know little about geoengineering in practice. “The need for research hasn’t gone away,” he says. Given carbon emissions are still rising, he expects geoengineering research to become more of a priority for the science community.

Solar geoengineering has vociferous critics in civic society. ETC Group, a Canada-based NGO, wants an immediate stop to any open-air projects, including Keith’s. Geoengineering’s problems, the group contends, include unintended impacts on the climate, governance questions – what if one country’s geoengineering negatively affects another country? – and promoting inaction on climate change.

Many find that last issue to be pertinent. Joanna Haigh, who recently retired from running the Grantham Institute for Climate Change and the Environment at Imperial College London, has called solar geoengineering a “fool’s paradise.” She fears it could become an excuse for not cutting emissions, and says the risk of side-effects from “playing God” with the climate is foolish.

Governments appear skittish about backing more research. At a United Nations Environment Programme meeting in March, the US and other countries blocked a resolution calling for a report into solar geoengineering, though this was partly due to disagreement between governments on what international body should oversee it.

Shuckburgh at Cambridge says greenhouse gas emissions clearly need to fall rapidly and substantially. “Given that, it is absolutely beholden on us to investigate all approaches for that, but [be] fully cognisant of the risks of any active intervention in the climate.”