spraying or injecting tiny airborne particles into the stratosphere

Reflecting sun’s rays would cause crops to fail, scientists warn

Research shows geoengineering method intended to combat climate change would have adverse effect on agriculture

— Proposals to combat climate change by reflecting the sun’s rays back into space would cause widespread crop failure, cancelling out any benefits to farming from the reduction in warming, according to new research.

By examining the effects of volcanic eruptions on agriculture – which has a similar effect to proposed artificial methods of scattering solar radiation through aerosols – scientists have concluded that such methods could have unintended consequences.

“[The research was to] find a way to examine the side effects of geoengineering without experimenting on the climate,” said Jonathan Proctor of University of California, Berkeley, lead author of the paper published in the peer review journal Nature. “[We found] potential adverse effect on agricultural production.”

But he said there could be other positive effects that were less easy to capture.

The findings deal another blow to proposals to use geoengineering to reduce or delay global warming, which some scientists think may be necessary to stave off the worst effects of rising greenhouse gas emissions.

solar geoengineering aims to cool the earth
Solar geoengineering aims to cool the Earth by injecting reflective particles, shown in blue, into the high atmosphere. Photograph: Jonathan Proctor and Solomon Hsiang/Nature

Spraying or injecting tiny airborne particles into the stratosphere has been regarded as one of the prime possibilities for geoengineering, by reflecting some of the sun’s rays back into space before they can warm the Earth.

The scientists studied the eruption of El Chichón in Mexico in 1982 and the eruption of Mount Pinatubo in the Philippines, both of which caused large quantities of sulphate particles to enter the stratosphere. This created a “veil” which reduced the amount of sunlight reaching the Earth’s surface.

In the study, the researchers examined the aerosol levels, solar radiation and crop yields. The deflection of sunlight had a negative effect on the yields of many staple crops, including rice, wheat and maize. They concluded that the impacts on crops of sending particles deliberately into the stratosphere would probably be similar, and that the beneficial effects on crop yields from the resulting cooling would be “essentially negated” by the loss in crops due to the reduction in sunlight, failing to remove the threat climate change poses to agriculture and food security.

Hugh Hunt, reader in engineering at Cambridge University, who was not involved in the research, said solar radiation management [SRM] was “no magic bullet”, but the effects should be compared with doing nothing. “We may well decide to use SRM to slow or reverse the melting of Arctic sea ice and to preserve the Greenland ice sheet. We will then be glad to have saved valuable land and the homes of millions of people from rising sea levels. Moreover, in an SRM world, agriculture will be sustained by a more stable and predictable climate,” he told the Guardian.

“SRM, rather like chemotherapy, is not something one would wish on a healthy planet. The Earth is sick and it is likely that any cure such as SRM will have unpleasant side effects. What we really ought to be doing is to halt the rise of atmospheric greenhouse gases, not just sometime in the future but now.”

Matthew Watson, of the school of Earth sciences at Bristol University, added: “It’s worth noting that this research only states that SRM would not necessarily improve crop yields and that there are other potential co-benefits and risks that must be carefully considered.”

Previous research has shown that the use of aerosols for geoengineering could have a substantial impact on weather patterns, for instance on the frequency and intensity of hurricanes, or could cause changes in rainfall such as droughts in vulnerable regions.

In the UK, the Spice (stratospheric particle injection for climate engineering) project was set up as a government-funded university collaboration in 2010 to examine the possibilities of aerosol-based geoengineering. It ended in 2015 and is understood to have queried the potential positive impacts of geoengineering, though findings have not yet been published. An experiment to mimic the effects of such a programme was abandoned.

mount pinatubo, philippines
Scientists studied a number of volcanic eruptions including Mount Pinatubo in the Philippines. Photograph: Arlan Naeg/AFP/Getty Images


Durwood Zaelke, president of the Institute for Governance and Sustainable Development in the US, who was not involved in the research, pointed out that the effects of sulphate particles can already be seen, as many coal plants which emit sulphates have been closed down. Cutting sulphates can produce a short-term warming effect, because the sulphates can deflect the sun’s rays, while cutting carbon dioxide emissions takes longer to have an effect.

He said: “There are other strategies for managing short-lived climate pollutants we should start with [including] cutting black carbon [soot, from fossil fuel burning], methane and HFC refrigerants. We need to think of climate change mitigation like a staggered race, where short-lived pollutants get a fast start and CO2 reductions eventually catch up and provide more and more cooling.” If these measures were taken, it could reduce temperature rises by up to 0.6°C by 2050 and by 1.2°C by the end of this century.

The research showed, he concluded, that “maybe we can keep geoengineering on the bench a bit longer while we figure out how to manage it safely”.

spraying or injecting tiny airborne particles into the stratosphere
Spraying or injecting tiny airborne particles into the stratosphere has been regarded as one of the prime possibilities for geoengineering, by reflecting some of the sun’s rays back into space before they can warm the Earth. Photograph: ISS/NASA


Stephen Salter, emeritus professor of engineering design at Edinburgh University, and an advocate of an alternative geoengineering method spraying the air to whiten clouds and increase their reflectivity, said: “The message is that we should not expect great agricultural improvements from stratospheric sulphur but negative results will be moderate. People who are hostile to geoengineering – there are lots of them – will argue that we are stuck with the results of stratospheric sulphur for a year or more and that there might be another Pinatubo or even something like the 1815 Tambora event, which gave the year without a summer.”

by Fiona Harvey | The Guardian