Radical departure: Block the sun to counter climate change?

Spencer Bokat-Lindell

Last month, a two-person start-up company by the name of Make Sunsets claimed that it had launched weather balloons filled with reflective sulfur particles into the sky somewhere over the coast of Baja California. More provocation than experiment, the launch was a first-of-its-kind field test of a climate intervention known as geoengineering: a branch of speculative technology that promises to counteract and even reverse global warming by altering Earth’s atmosphere.

Long a taboo idea among climate experts thought too dangerous even to research, geoengineering is becoming increasingly mainstream. In 2019, Congress gave the National Oceanic and Atmospheric Administration $4 million to research techniques like the one Make Sunsets just tested, and it has since drawn interest from the Biden administration. As the world continues to fall short of the goals of the Paris agreement and the costs of climate change mount, is geoengineering an idea worth taking seriously, or is it a world-historically reckless distraction from the global effort to transition away from fossil fuels? Here’s a look at the debate. In 1965, a group of scientific advisers delivered the first government report on global warming to President Lyndon Johnson. Warning of calamitous sea level rise, they called for exploring “the possibilities of deliberately bringing about countervailing climatic changes,” perhaps by brightening the oceans’ surface. Proposals for geoengineering have since evolved, and fall into two broad categories:

Carbon dioxide removal:

In recent years, a handful of companies have debuted machines capable of extracting carbon dioxide from the air for underground storage or use in products that contain the compound, a process called direct air capture. Other strategies for carbon removal include planting trees, fertilizing the oceans with iron to stimulate phytoplankton blooms and raising the pH of the oceans to increase their absorption of carbon dioxide and counteract the acidification that threatens marine ecosystems.

Solar radiation management:

In 1991, a volcano in the Philippines spewed 20 million tons of sun-blocking sulfur dioxide gas into the atmosphere, causing global temperatures to temporarily drop by about one degree Fahrenheit. This natural experiment provided the basis for the most well-known and controversial method of geoengineering, known as stratospheric aerosol injection. Other solar geoengineering proposals involve brightening marine clouds with sea salt, thinning a specific type of cloud that absorbs heat and, more far-fetched, shooting giant mirrors or reflective bubbles into space.

Carbon removal through direct air capture is typically considered a safe and elegant form of geoengineering, but the technology is nascent, inherently slow and prohibitively expensive. For those reasons, even its supporters argue that it is best thought of as a potential way to offset the emissions from the few industries that are hard to decarbonise, like aviation. Sulfur aerosol injection, on the other hand, would be relatively easy and cheap to deploy immediately at a planetary scale, costing as little as $2 billion per year.

Almost no proponents of geoengineering research champion it as a substitute for transitioning away from fossil fuels. Rather, they argue that it could help buy humanity more time to make that transition. They also point out that because carbon dioxide persists in the atmosphere for thousands of years, eliminating carbon emissions would only prevent the world from heating up further; it wouldn’t cool the world back down, at least not for anyone alive today. Even if the world managed to decarbonise by 2050, extreme weather events and sea level rise would pose a greater threat than they do now for many centuries to come.

“Emissions cuts are necessary,” David Keith, a professor of applied physics and public policy at Harvard, wrote in The Times in 2021. “But pretending that climate change can be solved with emissions cuts alone is a dangerous fantasy. If you want to reduce risks from the emissions already in the atmosphere — whether that’s to prevent forest fires in Algeria, heat waves in British Columbia or floods in Germany — you must look to carbon removal, solar geoengineering and local adaptation.”

If you find the prospect of experimenting on the atmosphere horrifying to contemplate, you’re not alone. Since last January, more than 360 climate and governance scholars have signed an open letter calling on national governments and the United Nations to restrict the development of solar engineering technology, contending that it poses an “unacceptable risk,” for three key reasons:

The side effects are too dangerous. Spraying sulfur into the stratosphere might bring down the earth’s temperature, but it could also turn the sky white, change weather patterns, increase the spread of malaria, deplete the ozone layer and alter the light that plants need to grow. Some regions might suffer while others benefit, creating the potential for conflict. “Imagine if India started pumping sulfur into the atmosphere only to see a huge drought hit Pakistan,” Bill McKibben wrote in The New Yorker last year. “Two nuclear powers, already at odds, with one convinced the other is harming its people.”

It’s a false hope. Skeptics of geoengineering warn that it could detract from efforts to transition away from fossil fuels if it were inaccurately perceived as an insurance policy against climate change. Individuals might put off taking steps to reduce their carbon footprints, for example. More concerning, parties with a large stake in the fossil fuel industry might lobby for pumping sulfur into the air as an alternative to keeping oil and gas in the ground. Make Sunsets, the start-up, is already selling “cooling credits” as carbon offsets. “Soon everyone who is dependent on coal, oil and gas will jump on the solar engineering bandwagon and say, ‘We can continue for 40 years with fossil fuels’ now,” Frank Biermann, a political scientist at Utrecht University, told The Guardian last month. “This debate threatens to derail current climate policies. It’s a huge risk.”

That risk stems in part from the fact that the cooling effect of sulfur lasts for only about one to two years. If humanity became dependent on aerosol injection as a substitute for decarbonisation rather than a complement, it could become a kind of civilisational addiction, impossible to safely stop.

Bokat-Lindell is a staff editor with NYT©2023

The New York Times