Geoengineering: Blocking the Sun

As global temperatures continue to rise and carbon emission targets remain elusive, the scientific community is revisiting a controversial “Plan B” for the planet. Stratospheric Aerosol Injection (SAI) involves spraying particles into the upper atmosphere to reflect sunlight back into space. While the science suggests it could rapidly cool the Earth, the ethical implications and physical risks have sparked an intense debate among researchers, policymakers, and environmentalists.

Understanding Stratospheric Aerosol Injection (SAI)

Stratospheric Aerosol Injection is a form of Solar Radiation Modification (SRM). The concept is inspired by natural volcanic eruptions. When Mount Pinatubo erupted in the Philippines in 1991, it spewed millions of tons of sulfur dioxide into the stratosphere. These particles created a haze that reflected enough sunlight to lower global temperatures by about 0.5 degrees Celsius (0.9 degrees Fahrenheit) for over a year.

SAI proponents suggest we could mimic this effect artificially. The theoretical process involves:

• Deployment: Specialized aircraft, high-altitude balloons, or artillery would deliver precursor gases (like sulfur dioxide) into the stratosphere, which sits about 10 to 50 kilometers above the Earth’s surface.
• Reflection: Once released, these gases convert into aerosol particles. These particles increase the Earth’s albedo, or reflectivity.
• Cooling: By reflecting a small percentage (roughly 1%) of incoming solar radiation, the planet would cool down, theoretically offsetting the warming caused by greenhouse gases.

The Experimentation Battleground

The transition from computer modeling to real-world testing has faced fierce opposition. The most prominent example is the Stratospheric Controlled Perturbation Experiment (SCoPEx), led by researchers at Harvard University.

The Rise and Fall of SCoPEx

The SCoPEx project aimed to launch a high-altitude balloon to release a small amount of calcium carbonate (chalk dust) into the stratosphere to study how the particles interacted with the air. It was intended to be a benign, small-scale physics experiment.

However, the project faced significant hurdles:

• Location Issues: Originally planned for the United States, the team moved the proposed launch to the Esrange Space Center in Kiruna, Sweden.
• Opposition: The Saami Council, representing the indigenous Saami people of the region, vehemently opposed the test. They argued that it violated their worldview regarding nature and posed existential risks without global consensus.
• Cancellation: In March 2024, Harvard officially announced the termination of the SCoPEx project following the recommendation of its independent advisory committee. This marked a major victory for opponents of geoengineering and highlighted the difficulty of conducting even minor field tests.

Rogue Actors: “Make Sunsets”

While academic institutions move slowly, private entities have moved faster. A startup called “Make Sunsets” claimed to have launched weather balloons containing sulfur dioxide in Baja California, Mexico, in late 2022. They attempted to sell “cooling credits” to the public.

The reaction was swift. The Mexican government announced a ban on solar geoengineering experiments within its territory, citing a lack of international agreements and potential environmental risks. This incident showcased the “rogue actor” risk, where a private company or single individual could attempt to alter the climate without oversight.

Critical Risks and Dangers

While SAI might cool the planet, the side effects could be catastrophic. Scientists point to three primary physical risks.

1. Termination Shock

Perhaps the greatest danger is “termination shock.” If we begin injecting aerosols and mask the heating caused by carbon dioxide, we must continue doing it indefinitely (or until carbon levels drop). If the system stops suddenly due to war, economic collapse, or terrorism, the stored-up warming would unleash all at once. Global temperatures could spike rapidly within a few years, a rate of change that would likely wipe out ecosystems and agriculture that cannot adapt quickly enough.

2. Disruption of Rainfall Patterns

Changing the temperature of the atmosphere affects the hydrological cycle. Models suggest that cooling the planet unevenly could shift the Intertropical Convergence Zone (ITCZ). This shift could disrupt the Asian and African monsoons, potentially causing massive droughts in regions that rely on seasonal rains for agriculture, affecting the food security of billions of people in the Global South.

3. Ozone Layer Depletion

The ozone layer is finally healing after the phasing out of CFCs. However, sulfate aerosols provide a surface for chemical reactions that destroy ozone molecules. Injecting large amounts of sulfur into the stratosphere could delay the recovery of the ozone layer by decades, increasing the amount of harmful UV radiation reaching the surface.

The Ethical and Political Debate

Beyond the physics, the governance of the sky presents an unprecedented ethical dilemma.

• The Moral Hazard: Critics argue that the mere existence of a “technological fix” creates a moral hazard. If politicians and corporations believe they can simply dim the sun, they may lose the political will to cut emissions. This could lead to a scenario where carbon continues to accumulate, making the “termination shock” risk even higher.
• Who Controls the Thermostat?: There is no global framework for deciding the Earth’s ideal temperature. Russia might prefer a warmer world for agriculture, while India needs a cooler one to survive heatwaves. If one country acts unilaterally to cool the planet, and it causes a drought in a neighboring country, it could be interpreted as an act of geopolitical aggression.
• U.S. Government Involvement: In June 2023, the White House Office of Science and Technology Policy (OSTP) released a congressionally mandated report outlining a research plan for solar radiation modification. While the report stated the Biden-Harris Administration has no plans to deploy the technology, the move signals that the U.S. government is taking the possibility seriously enough to formalize a research strategy.

Frequently Asked Questions

Is anyone currently blocking the sun to cool the Earth? No. Aside from small, unauthorized attempts by startups like Make Sunsets, there is no large-scale deployment of stratospheric aerosol injection happening today.

How much would it cost to deploy SAI? Estimates vary, but compared to the trillions required to decarbonize the global economy, SAI is surprisingly cheap. Some studies suggest a program could cost between \(2 billion and \)10 billion per year, which makes it financially accessible to many individual nations or even wealthy billionaires.

Can we just stop if it goes wrong? Technically, yes, but the consequences would be severe. The particles naturally fall out of the stratosphere after a year or two. However, stopping abruptly would trigger “termination shock,” causing rapid and dangerous warming.

Does this remove carbon dioxide from the air? No. Solar geoengineering is a “mask.” It treats the symptom (heat) but ignores the underlying disease (excess greenhouse gases). It also does nothing to address ocean acidification, which is caused by high \(CO_2\) levels.