Solar Geoengineering: The Science and Controversy of Dimming the Sun

As global temperatures continue to break records, a radical idea is moving from the fringes of science fiction to serious policy debates. This concept is known as solar geoengineering. Specifically, scientists and startups are investigating Stratospheric Aerosol Injection (SAI). This involves spraying reflective particles into the upper atmosphere to bounce sunlight back into space. While it could theoretically cool the planet quickly, the risks remain largely unknown and potentially catastrophic.

Understanding Stratospheric Aerosol Injection (SAI)

The core premise of SAI is simple. If we block a small percentage of incoming solar radiation, we can lower the Earth’s surface temperature. This process mimics a natural phenomenon known as the “volcanic winter.”

When Mount Pinatubo erupted in the Philippines in 1991, it blasted roughly 20 million tons of sulfur dioxide into the stratosphere. This created a global haze of sulfuric acid droplets that reflected sunlight. Over the following 15 months, global average temperatures dropped by about 0.5 degrees Celsius (0.9 degrees Fahrenheit).

Proponents of solar geoengineering suggest we can replicate this effect artificially. Instead of volcanoes, we would use:

• Specialized Aircraft: High-altitude planes designed to fly roughly 20 kilometers (12 miles) up.
• Weather Balloons: High-altitude balloons capable of dispersing payloads.
• Artillery: Guns capable of firing canisters into the upper atmosphere.

The primary material proposed for this is sulfur dioxide, though researchers are also looking at calcium carbonate or diamond dust, which might have fewer side effects on the ozone layer.

The Rogue Actors: Make Sunsets

The debate shifted from theoretical research to real-world action in late 2022. A startup called Make Sunsets, founded by Luke Iseman, launched weather balloons containing sulfur dioxide from a site in Baja California, Mexico. They did this without public engagement or scientific oversight.

This act caused an immediate backlash. The Mexican government announced a ban on solar geoengineering experiments in January 2023 to protect communities and the environment. Despite the ban in Mexico, Make Sunsets moved operations to the United States. In February 2023, they launched three balloons from Reno, Nevada.

This incident highlighted a major fear among climate scientists. The technology is cheap and accessible enough that a single company or a small nation could unilaterally decide to alter the global climate. Make Sunsets sells “cooling credits” for as little as $10, claiming to offset the warming effect of one ton of carbon dioxide.

The Harvard SCoPEx Project

While startups push ahead, academic research has faced stiff resistance. The most prominent example is the Stratospheric Controlled Perturbation Experiment (SCoPEx), led by researchers at Harvard University.

The project aimed to launch a balloon to release a small amount of calcium carbonate (less than two kilograms) to study how the particles interact with light and air chemistry. It was not intended to cool the planet but to gather data.

However, the proposed test flight in Kiruna, Sweden, was cancelled in 2021. The Saami Council, representing the indigenous Saami people of the region, strongly opposed the test. They argued that it violated their worldview and that there are no acceptable mechanisms for governing planetary manipulation. In March 2024, Harvard announced the project would be suspended definitively. This failure demonstrates that the social and political hurdles to geoengineering are just as high as the technical ones.

The Dangers of Playing God with the Weather

Spraying aerosols into the stratosphere carries significant risks. It is not a cure for climate change because it does not remove carbon dioxide from the atmosphere. It only masks the warming.

The Threat to the Ozone Layer

The sulfuric acid clouds created by SAI provide a surface for chemical reactions that destroy ozone. The 1991 Pinatubo eruption caused a temporary thinning of the ozone layer. Replicating this artificially could widen the ozone hole over Antarctica and delay its recovery by decades.

Disrupted Rainfall Patterns

Altering the planet’s heat balance changes how air moves. Climate models suggest that solar geoengineering could disrupt the Asian and African summer monsoons. This would be disastrous for billions of people who rely on these seasonal rains for agriculture. One region might get relief from heat waves, while another faces catastrophic drought.

Termination Shock

The most terrifying risk is known as “termination shock.” Carbon dioxide stays in the atmosphere for centuries. Aerosols fall out of the sky in a year or two. If we start a geoengineering program and then stop suddenly (due to war, terrorism, or economic collapse), the cooling mask would disappear rapidly.

The pent-up warming would hit the planet all at once. Temperatures could spike by several degrees within a decade. This rapid change would be impossible for ecosystems and human societies to adapt to.

Government Involvement and Future Research

Despite the controversy, major governments are taking a closer look. They realize that if another country starts spraying, they need to understand the science to respond.

In June 2023, the White House Office of Science and Technology Policy (OSTP) released a congressionally mandated report. It outlined a research plan to understand the risks and benefits of solar radiation modification. The report emphasized that the U.S. government has no current plans to deploy the technology, but it acknowledged the need to study it.

Similarly, the European Union called for an international assessment of the risks in mid-2023. They noted that the current state of governance is insufficient to manage a technology that affects the entire globe.

The scientific community remains divided. In 2022, over 400 scientists signed an open letter calling for an International Non-Use Agreement on Solar Geoengineering. They argue that the technology is ungovernable and presents an unacceptable risk to global stability. Conversely, groups like the Climate Overshoot Commission argue that we must research it as a potential emergency brake if climate tipping points are triggered.

Frequently Asked Questions

Is solar geoengineering illegal? There is no comprehensive global treaty banning it. However, the UN Convention on Biological Diversity has a moratorium on large-scale geoengineering activities. Individual countries, like Mexico, have enacted specific bans.

How much would it cost to cool the Earth? Estimates suggest a program could cost between \(10 billion and \)20 billion per year. In the context of the global economy, this is incredibly cheap. This low cost is what makes it dangerous, as it allows smaller nations or billionaires to potentially act alone.

Does this solve ocean acidification? No. Solar geoengineering only reduces sunlight. It does nothing to lower CO2 levels. Therefore, the oceans would continue to absorb carbon dioxide and become more acidic, threatening coral reefs and marine life.

Are there alternatives to sulfur dioxide? Yes. Researchers are investigating diamond dust, alumina, and calcite. These materials might reflect sunlight with less impact on the ozone layer or stratospheric heating, but research is still in the early computer-modeling stages.