Scientists Want to Block Out the Sun. Is it Even Possible?

Scientists Want to Block Out the Sun. Is it Even Possible?
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Scientists are seriously considering blocking the Sun. To be more specific, they want to use a technique known as solar geoengineering to reflect a portion of the sunlight that reaches Earth back out into the Solar System.

According to a March report by the United States National Academies of Sciences, Engineering, and Medicine (NASEM), more research into the viability of solar geoengineering as a means of combating climate change should be conducted. Caution is advised, however, because the method has the potential to exacerbate the problem it seeks to solve.


Though solar geoengineering has the potential to reduce the effects of global warming, it is a contentious method that some see as a potentially disastrous process that could obliterate the sky and plunge us headfirst into a dystopian reality. Others believe the IPCC’s latest report, dubbed “code red for humanity” by UN Secretary-General António Guterres, calls for drastic action and innovative solutions, and that we must simply pursue all available tools.

Can we afford to turn a blind eye to solar geoengineering?

Without extraordinary measures, the latest models predict that global temperatures will exceed 4 °C above preindustrial levels by the end of the century, implying that the 2015 Paris Agreement — which aims to keep the rise below 2 °C — will have been an unmitigated failure.

“Anyone who reads the latest IPCC report on Climate Change will have to agree that we are either extremely close to, or already past, the point of no return in terms of keeping global temperature increases to below 2 °C vs pre-industrial levels, which could trigger catastrophic cycles of events,” Robert Laswell, editor for renewable energy firm Semprius, told us via email. “That means nothing should be off-limits.” Laswell asserted that research into solar geoengineering, “from ocean sulfur cycle enhancement to stratospheric aerosol injection,” should “begin receiving significant funding now” before these become “a last resort option when it’s already too late.”


This is the same thinking that underpins the NASEM report, which emphasizes the importance of method research above all else. Chris Field, an environmental scientist at Stanford University who chaired the NASEM committee behind the report, recently stated in an interview with Physics Today: “We are at a critical juncture in the fight against climate change. We understand how difficult it is to make societal changes that result in zero greenhouse gas emissions. That difficulty is a compelling reason to understand the entire portfolio of options.” Many scientists appear to agree that we simply cannot afford to ignore the potential benefits of solar geoengineering.

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The dangers of solar geoengineering may outweigh the benefits.

The catch — and it’s a big one — is that blocking out a portion of the sunlight that reaches us from the center of our Solar System carries significant risks. The Union of Concerned Scientists (UCS), for example, emphasizes the risk of “moral hazard” — the risk that solar geoengineering will be used as an excuse to slow CO2 emission reductions, thereby failing to address the root cause of climate change.

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“Calling for solar geoengineering is an increasingly desperate and lame excuse to prop up the failing fossil fuel industry,” Western University’s Joshua M. Pearce, Ph.D. told us in an interview. Pearce claims that “To mitigate climate change, we don’t need solar geoengineering; we just need to get out of the way and let economics take its course. Solar photovoltaic technology is now the fastest growing and least expensive way to generate electricity. Coal-fired electricity is no longer economically viable, as evidenced by one coal bankruptcy after another.”


Pearce, who recently published a study demonstrating that replacing natural gas heating with a combination of solar power and heat pump systems is cost effective, stated that “Without resorting to solar geoengineering, electrification of transportation and heating, with renewable energy taking over the electric markets, will solve our climate challenges. It is past time to stop attempting to save antiquated fossil fuel technologies and instead hasten their demise.”

Crucially, we know very little about how a sustained solar geoengineering drive might affect regional weather patterns — most research to date has been limited to observations on the environmental impact of volcanic eruptions. Millions of dollars could be invested in testing the method, only for scientists to conclude that it cannot be safely deployed on a large scale.

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Several methods for obstructing the Sun are being developed.


The two main methods for solar geoengineering are stratospheric aerosol injection (SAI), which involves spraying reflecting particles, or aerosols, into the upper atmosphere, and marine cloud brightening (MCB), which uses sea salt to encourage additional cloud formation over the ocean.


In January of this year, it was reported that Bill Gates had backed a proposal by Harvard scientists to conduct an experiment to test the viability of SAI.

The Stratospheric Controlled Perturbation Experiment (SCoPEx) scientists postponed a test flight scheduled for this year due to an outcry from environmentalists. If it goes ahead, the experiment will cost around $20 million and will aim to release approximately 2 Kg of chemicals into the stratosphere, including sulfates and calcium carbonate.

Last month, Australian researchers announced that they will test a type of marine cloud brightening to help reduce coral bleaching on the Great Barrier Reef, which is being caused by increased heat stress in the region as a result of climate change.


Despite the controversy surrounding solar geoengineering and the warnings of experts, several scientists and firms continue to make proposals as the Earth’s temperature continues to rise to record levels.

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