September 24, 2024 By Mark Fischetti
More and more climate scientists are supporting experiments to cool Earth by altering the stratosphere or the ocean
As recently as 10 years ago most scientists I interviewed and heard speak at conferences did not support geoengineering as a way to counteract climate change. Whether the idea was to release large amounts of sulfur dioxide into the stratosphere to “block” the sun’s heating or to spread iron across the ocean to supercharge algae that breathe in carbon dioxide, researchers resisted on principle: don’t mess with natural systems because unintended consequences could ruin Earth. They also worried that trying the techniques even at a small scale could be a slippery slope to wider deployment, and that countries would use the promise of geoengineering as an excuse to keep burning carbon-emitting fossil fuels.
But today more and more climate scientists openly support experimenting with these and other proposed strategies, in part because entrepreneurs and organizations are going ahead with the methods anyway—often based on little data or field trials. Scientists want to run controlled experiments to see if the methods are productive, to test consequences and perhaps to show objectively that the approaches can cause serious problems.
“We do need to try the techniques to figure them out,” says Rob Jackson, a professor at Stanford University, chair of the international research partnership Global Carbon Project and author of a book on climate solutions called Into the Clear Blue Sky (Scribner, 2024). “But doing research does make them more likely to happen. That is the knotty part of all this.”
A tacit race may be starting among scientists and entrepreneurs. More funding is being offered to researchers, and investments are growing in companies that would pursue geoengineering. In 2023 a start-up called Make Sunsets launched balloons containing sulfur dioxide into the stratosphere, selling “cooling credits” to companies and individuals. In early September, 23 academics at the not-for-profit consortium Exploring Ocean Iron Solutions unveiled a plan to assess how much CO2 iron fertilization could sequester in the deep sea, and they hope to start trials across the northeastern Pacific Ocean in 2026. Big corporations, including oil companies, are already building large industrial facilities to pull CO2 from the air, and the U.S. government is offering them billions of dollars.
There is confusion, too. Some scientists say the term “geoengineering” should refer only to techniques that alter Earth systems. For example, sulfur dioxide in the stratosphere creates tiny droplets that reflect incoming sunlight back to space, an approach called solar radiation management (SRM). But this method could also affect weather patterns or weaken the ozone layer that protects us from ultraviolet radiation. Brightening clouds by spraying them with ocean mist from below can reduce sunlight but could interfere with rain patterns. Spreading iron across the ocean helps phytoplankton to grow and consume CO2, yet these organisms would also consume other nutrients, which could possibly starvesea life. Spreading certain kinds of pulverized rock across the sea surface can make the water more alkaline, allowing it to absorb more CO2 from the air, but it could affect ocean chemistry, too.
In contrast, using machines to pull CO2 from the air, a technique known as direct air capture (DAC), doesn’t directly interfere with natural systems and so shouldn’t be called geoengineering, some argue. Social concerns could still be high, however; for example, millions of these machines would be needed to reduce warming by a meaningful extent, and that would require huge amounts of energy. If they were powered by wind and solar, as they ideally would be to avoid more greenhouse gas emissions, the installations could compete with agriculture for land.
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