Blocking the sun will not prevent crop damage from global warming

Injecting particles into the air to cool the planet and prevent the warming effect of climate change would not prevent crop damage from rising temperatures, according to new research.

Scientists at the University of California, Berkeley, analysed the effects of ‘Earth-cooling’ volcanic eruptions, and the response of crops to the changes in sunlight. They identified that improvements in the yield gained would be negated by lower productivity because of reduced sunlight.

“Shading the planet keeps things cooler, which helps crops grow better. But plants also need sunlight to grow, so blocking sunlight can affect growth. For agriculture, the unintended impacts of solar geoengineering are equal in magnitude to the benefits,” said lead author Jonathan Proctor, a PhD student at UC Berkeley in the Department of Agricultural and Resource Economics.

“It’s a bit like performing an experimental surgery; the side-effects of treatment appear to be as bad as the illness.”

“Unknown unknowns make everybody nervous when it comes to global policies, as they should,” said Dr Solomon Hsiang, co-lead author of the study and Chancellor’s Associate Professor of Public Policy at UC Berkeley.

“The problem in figuring out the consequences of solar geoengineering is that we can’t do a planetary-scale experiment without actually deploying the technology. The breakthrough here was realising that we could learn something by studying the effects of giant volcanic eruptions that geoengineering tries to copy.”

The proposition was that sulphate aerosols, minute drops of sulphuric acid, could be injected into the upper atmosphere to artificially cool the Earth, in turn alleviating the greenhouse warming effect caused by increasing levels of carbon dioxide. These minute drops would reflect a small percentage of sunlight back into space, and as such would reduce the temperature by a few degrees.

“It’s like putting an umbrella over your head when you’re hot,” Proctor said. “If you put a global sunshade up, it would slow warming.”

“It’s similar to using one credit card to pay off another credit card: at the end of the day, you end up where you started without having solved the problem,” Dr Hsiang said.

Earlier studies have suggested that aerosols may improve crop yields by scattering sunlight and allowing the suns energy to reach more interior leaves, ordinarily shaded by the ones above. The benefit of this scattering could be weaker than previously proposed.

“We are the first to use actual experimental and observational evidence to get at the total impacts that sulphate-based geoengineering might have on yields,” Proctor said. “Before I started the study, I thought the net impact of changes in sunlight would be positive, so I was quite surprised by the finding that scattering light decreases yields.”

Despite the conclusions of the study, Proctor said, “I don’t think we should necessarily write off solar geoengineering. For agriculture, it might not work that well, but there are other sectors of the economy that could potentially benefit substantially.”

“The most certain way to reduce damages to crops and, in turn, people’s livelihood and well-being, is reducing carbon emissions,” he added.

The study was published in Nature.