The World’s Scientists Are Arguing About Whether or Not to Block the Sun

finger pointing at the sun
Scientists Are Arguing About Blocking the SunTravelpix Ltd - Getty Images
  • Three scientists are arguing against solar geoengineering after a recent UN controversy.

  • Solar geoengineering is the hypothetical bouncing back of solar radiation using technology. It’s often proposed as a potential avenue to help stave off the effects of climate change.

  • Credible proponents say this is strictly a last resort that they want to test just in case.

Recently, Switzerland proposed that the United Nations (UN) form an “expert group” on solar geoengineering—a controversial area of study that revolves around the use of technology to block the Sun from continuing to change our climate. The group did not come to fruition, because UN nations argued too much about what such a group could do or accomplish—solar geoengineering is just that much of a hot-button topic, even though it's largely hypothetical at this point. Are we missing a great opportunity to course correct our own climate in realtime? (TL;DR: Many researchers say no.)

Geoengineering, or climate engineering, is an umbrella term for any actions that try to change the climate of Earth itself artificially. Terraforming, as depicted in science fiction, is also a form of geoengineering—it turns “lifeless” planets (usually with either a hostile atmosphere or none at all) into ones that human beings can inhabit by establishing the same air and water cycles we have on Earth. Solar geoengineering is a specific branch that seeks to change the climate by blocking the Sun with reflective materials. If solar radiation bounces off, proponents argue, then the Earth’s climate will cool.

In response to Switzerland’s call for an expert group, three researchers from James Cook University in Australia and Wageningen University in the Netherlands published an essay on The Conversation, calling solar geoengineering a “dangerous distraction.” They claim that, over time, research has pointed out potential risks that they feel aren’t worth the potential rewards: unpredictable effects, biodiversity loss, undermining food security, and intergenerational human rights violations. “Calls for outdoor experimentation of the technologies are misguided and detract energy and resources from what we need to do today: phase out fossil fuels and accelerate a just transition worldwide,” they conclude.

In 2024, science itself can be very controversial, and climate science arguably moreso. That’s not because of science itself, usually, but because of small-P politics like the “optics” of a particular study or the media’s efforts to fan engagement as a way to generate more revenue. On top of that, solar geoengineering is scientifically controversial. Solar geoengineering has also probably struggled a bit after being the villain in some high-profile fictional stories, like the iconic 1995 The Simpsons two-parter "Who Shot Mr. Burns?" and the 2013 dystopian movie Snowpiercer.

In 2021, Harvard University pulled a high-profile planned solar geoengineering experiment after outraged backlash against even a small pilot study on the instruments they might use to deliver particles into the atmosphere to block the Sun—not even the particles themselves, but a test of a balloon and some other instruments, with no particles involved at all. To those who opposed it, like the indigenous Saami people of Sweden, who make up some of the local population of the proposed study area, it seemed like any study of an outlandish-seeming idea was the first step down a slippery moral slope.

In 2022, Massachusetts Institute of Technology (MIT) proposed a space-based solar geoengineering study as a compromise that they said would be safer for Earth, as it involved blocking the Sun from outer space rather that our own already troubled atmosphere. MIT’s website for the idea boils down the proponents’ argument for solar geoengineering studies: “If climate change has already gone too far, what could be our emergency solutions? Geoengineering might be our final and only option.”

The term “emergency” is key in the debate over solar geoengineering. After decades of relative inaction, scientists are more and more frustrated and even panicked over the climate crisis. Switzerland’s delegation to the UN asked only for a group that could discuss solar geoengineering, even if that group gathered up all the skepticism and research papers and made a repository of that information for others to use.

In the essay on The Conversation, the researchers speak in hypotheticals as though they’re facts—for example, they state that certain technologies would take one hundred years of continuous use. The thing is, these science-based guesses are still subject to the unexpected consequences that use in the real world might cause—and that’s something we can’t know unless scientists, somewhere, are allowed to do experiments of some kind. It will also take that long to “phase out fossil fuels” around the world, and that also has complex implications for the food supply and human rights.

The writers point out that one ongoing experiment with seawater reflection (in the Great Barrier Reef, off the coast of Australia) has been a failure, producing no meaningful effect on water temperature. That’s great data to have. It’s something concrete that we can use to close the book on an idea that doesn’t work. But treating solar geoengineering like the flat Earth conspiracy theory—like even talking about it is a harmful indulgence—won’t help climate science or humankind.

During the UN proceedings, nations from the so-called “Global South,” a term referring to developing and decolonizing places around the world, called for “non-use” of solar geoengineering. Indeed, we can honor that request while still doing real world research studies that will show the beginnings of unintended consequences and other potential fallout from solar geoengineering. That can take place alongside today’s urgent calls for reductions of emissions.

The proof of the pudding is in the eating, as they say. If you’re preparing a meatloaf and you need to taste it for seasoning, you take a tiny bit and cook it quickly so you can try it. A discussion of solar geoengineering doesn’t have to be more than that tiny morsel, but without it, we may never know if the meatloaf is good or bad.

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