Overshoot Commission calls for research into solar geoengineering

Dimming the sun could “complement” emissions cuts, says panel of leaders, while acknowledging concerns about the risks

Overshoot Commission calls for research into solar geoengineering

Solar radiation modification aims to mask the effect of climate change by reflecting more sunlight back into space. Photo: Luis Boza/Unsplash


Governments should expand research into controversial solar geoengineering, while placing a moratorium on large-scale experiments outdoors, a panel of leaders has recommended.

The Overshoot Commission was set up last year to examine ways of reducing risks if and when global heating surpasses 1.5C.

In a report published on Thursday, it called for an acceleration in emission reductions, more resources to adapt to the impact of climate change and scaling up technologies to suck carbon dioxide from the atmosphere.

The Commission also called for international discussions and scientific research on solar radiation modification (SRM). The technology aims to reduce the amount of sunlight reaching the planet’s surface. This could be achieved by pumping aerosols into the high atmosphere or by whitening clouds.

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Its proponents say it could be a relatively cheap and fast way to counter extreme heat. But it would only temporarily mask the impact of rising emissions, not tackle the root cause. The regional effects of manipulating the weather are hard to predict and risk worsening climate impacts in some places.

The report acknowledged the technology’s potential drawbacks, but refused to take the option off the table. “It would be imprudent not to investigate or discuss SRM because present evidence suggests the possibility it could complement other approaches,” the Commission wrote.

During a press conference, its president Pascal Lamy said appeals not to discuss solar geoengineering “feel fickle” and “not the way to go”.

A fractured debate

Scientists Climate Home News were divided on the wisdom of this approach.

“The report creates a sort of parity between acknowledging the need for emission reductions and elevating technologically uncertain or even dangerous management options,” said Ben Sanderson, a climate scientist at CICERO. “By expanding research, the idea of SRM gets increasingly normalised, while distracting from real climate mitigation”.

James Haywood, Professor of Atmospheric Science at the University of Exeter, argued the Commission struck a reasonable balance between risks and opportunities. “Current conventional mitigation efforts are widely acknowledged to be insufficient to maintain global mean climate temperatures below 1.5C,” he said. “It therefore makes a great deal of sense to research whether SRM proposals could be used to reduce the worst impacts of climate change.”

‘No stone unturned’

Hosted by the Paris Peace Forum, the commission comprises 13 global leaders, including former presidents and ministers.

Its president Pascal Lamy said “we have to leave no stone unturned”, as the world is on track to exceed the 1.5C goal set by the Paris Agreement. Temperature rises of up to 2.6C can be expected based on current climate plans, according to the UN’s global stocktake report released last week.

As efforts to reduce emissions fall short, geoengineering options become increasingly tempting. Most are highly speculative and there are no global rules on what countries or companies can do.

A rogue SRM experiment conducted by a US startup in Mexico’s northern state of Baja California led the government to announce a ban on solar geoengineering.

Moratorium calls

The Commission said countries should introduce a moratorium on “the deployment or large-scale experiments” of SRM. The ban should apply to any activity with “risk of significant transboundary harm” and should stay in place until the scientific community gains a better understanding of the technology.

Chukwumerije Okereke, professor of Global Climate Governance and Public Policy at Bristol University, argues the moratorium is poorly defined and calls for a total pause on experiments. “What does large-scale mean? This could lead to rogue researchers making a test at a time when we don’t even know the full effects,” he added. “This is not a position that is ethical, sensible and recognises the dangers.”

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Many scientists are concerned SRM could create damage the ozone layer or inequally distribute extreme weather events like droughts or flooding across the world.

There are also questions about how long this technology would be needed and what happens after it is stopped. Ben Sanderson says early modelling indicates that cessation could fast-track severe disruption, with the potential to experience decades’ worth of changes in a year. “We would live in a high-risk world,” he added.

Moral hazard

Central to the geoengineering debate is the so-called moral hazard argument: the idea that researching technologies to remove CO2 or mask its effects undermines support for existing climate policies.

The Commission says the priority is to accelerate emission cuts by replacing fossil fuels and transitioning to clean energy. It also says technologies like SRM and carbon removal should only be seen as additional measures.

Laurence Tubiana, one of the commission’s members, tweeted that “we cannot be fooled by the false promises of simple techno-fix solutions”.

But Carl-Friedrich Schleussner, a scientist at Climate Analytics, believes simply putting the option on the table relieves pressure from the obligation to reduce emissions. “Giving it a prominent space on the agenda has a negative effect,” he said.

Carbon removal push

Alongside SRM, the Commission pushed for a faster development of carbon dioxide removal (CDR). The term comprises a vast number of methods to remove CO2 from the atmosphere: from natural activities like tree planting to technological ones such as direct air capture.

The report says governments should promote a rapid expansion of “higher quality CDR at scale” by incentivising innovation, including through subsidies.

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The use of CDR is the subject of much debate in the climate policy world. Activities like tree planting need vast swathes of land and carry the risk of releasing pollutants back into the atmosphere in case of a forest fire.

Direct air capture is energy hungry and expensive at the moment.

The International Energy Agency estimates that removing a ton of carbon dioxide costs between $135 and $135 with DAC today – although this could drop to below $100 by 2030.

According to the IPCC scientists, this is far more expensive than reducing emissions with renewable energy or energy efficiency.

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