Solar geoengineering: a complete explanation, techniques, risks, and debate

The advance of climate change and the inadequacy of global efforts to reduce emissions have led scientists, experts, and international organizations to consider "out-of-the-box" solutions. Among these, the following stands out: solar geoengineering, a field that, although it may sound like science fiction, is being debated more and more each day in offices, laboratories and international political forums.

For some years now, concepts that were previously reserved for novels and movies have become the subject of technical research and million-dollar budgets. Can we, or should we, really manipulate Earth's climate to cool the planet? What is solar geoengineering, what are its techniques, risks, possibilities, and controversies? If you're wondering why there's so much fuss about this topic and want to understand all the nuances, here's a comprehensive, well-documented, and easy-to-understand guide on the subject.

The context: the global challenge of warming and the effects of extreme weather

The planet is in a climatic situation never before seen in the recent human eraIn recent years, global heat records have been broken, with average temperatures exceeding, for the first time, the dreaded 1,5°C threshold above pre-industrial levels (1850-1900). Melting polar ice caps and glaciers, a 20-centimeter rise in sea level since 1880 (according to NASA), more frequent and intense heat waves, torrential rains, droughts, wildfires, and unpredictable seasonal shifts have become commonplace.

The main causes are anthropogenic.Emissions of carbon dioxide, methane, and nitrogen oxides—resulting from the burning of fossil fuels, deforestation, and intensive agriculture—have disrupted the planet's fragile energy balance. Since the 19th century, CO₂ levels have risen by more than 40%, methane by 150%, and nitrous oxide by nearly 20%. The result is an atmosphere that retains more heat, depriving the Earth of its traditional thermal regulation.

The human impact is brutal and unequal.The WHO warns of up to 250.000 additional deaths per year from climate-related diseases between 2030 and 2050. Food security is faltering, poverty is worsening, and more and more people are facing forced displacement or natural disasters.

Why is solar geoengineering emerging?

The big challenge is to prevent the global temperature from continuing to rise above that famous 1,5°CIf temperatures exceed 2°C, the disaster scenario could be much worse: massive loss of biodiversity, unmanageable migrations, infrastructure collapse, and global political risks.

Policies to mitigate emissions, such as the Paris Agreement or the transition to renewable energy, are progressing more slowly than desired.Hence, part of the scientific community —approximately two-thirds, according to recent surveys— considers solar geoengineering to be a "plan B," an emergency measure to buy time while efforts are made to address the problem at its source.

What is solar geoengineering?

Solar geoengineering, also called Solar Radiation Modification (SRM), encompasses techniques designed to reduce the amount of solar radiation that reaches the Earth's surface.The goal: to artificially 'refresh' the planet. It does not eliminate greenhouse gases, nor does it solve the root of the problem, but rather compensates for some of its effects to provide room for action in the face of climate collapse..

These techniques are still in the research phase, with some highly controlled field experiments and numerous computer simulations. Their large-scale applications are currently speculative, and none have yet been tested on a massive scale. However, interest in and investment in this field are growing every year.

There are several proposals under the label of solar geoengineeringBelow, we review the most relevant ones, according to technical reports, scientific publications, and specialized organizations:

• Stratospheric aerosol injection (SAI)This involves releasing reflective particles, usually sulfur dioxide, into the stratosphere (between 10 and 50 km altitude). The mechanism is similar to that of a large volcanic eruption, which causes a temporary drop in global temperature by reflecting some of the sun's radiation back into space. Proposals include using high-altitude aircraft or balloons to disperse the aerosols in a controlled manner, creating a kind of reflective curtain.
• Marine cloud bleaching (MCB)The aim here is to increase the ability of low-lying clouds over the oceans to reflect sunlight. This is typically achieved by spraying saltwater, using specialized vessels capable of generating particles that make the clouds appear "whiter" and more reflective.
• Cirrus thinning or modification (CCT)In this case, the aim is to modify high-altitude ice clouds to increase their transparency and facilitate the escape of terrestrial thermal radiation into space. The exact properties of cirrus clouds and their ability to be modified are still being investigated, and the results are quite mixed.
• Space sunshades and orbital mirrorsAn even more futuristic proposal. It consists of placing immense mirrors, discs or lenses in space (at strategic points between the Earth and the Sun) to deflect some of the solar energy.
• Increased surface albedo (SAM)The idea here is to increase the reflectivity of the Earth's surface with more "ground-level" methods, such as painting roofs white, covering the Arctic with reflective microspheres, or even modifying crops to be lighter in color.

How much progress has been made? Projects, experiments, and modeling

Institutional and scientific interest in solar geoengineering has grown considerably in the last decadeFor example, in the United States, top-tier institutions such as the National Academies of Sciences, Engineering, and Medicine (NASThey proposed a program in 2021 research national with funding of $200 million over five years, focused on feasibility and risk-benefit assessment.

Large-scale experiments are very restrictedHowever, there are specific, small-scale pieces of evidence:

• Stratospheric Controlled Perturbation Experiment (SCoPEx)A project led by Harvard University plans to release minute amounts of mineral dust into the stratosphere using balloons to observe how aerosols behave and gather data on their effects. You can read more on their website. Official Site.
• Marine cloud bleaching projectsSome testing attempts in California, Australia and elsewhere have been suspended or slowed by public pressure or lack of public consultation.
• Climate modelingMost of our knowledge comes from computer simulations. Models have shown that aerosol injection, for example, could cool the Earth, but there is enormous uncertainty about the side effects and the accuracy of the results, since atmospheric processes occur on scales that are difficult to fully reproduce.

Do these techniques work? Benefits and potential

The appeal of solar geoengineering lies in the fact that, at least in theory, it could cool the planet relatively quickly and provide some leeway in the face of global warming.A controlled drop in temperature would add precious time for adaptation and decarbonization.

However, no large-scale experiment has yet tested the hypotheses.The success scenarios are based primarily on simulations and the analogy with large volcanic eruptions.

What are the risks and unknowns?

La The list of doubts, risks, and questions is just as extensive, or even more so, than the list of potential advantages.The most notable dangers include:

• Regional climate changesThe redistribution of solar radiation can modify rainfall patterns (such as monsoons in Asia and Africa), alter winds, and even influence the frequency or strength of cyclones and hurricanes.
• Impact on public health and ecosystemsChanges in local or global climate affect agriculture, biodiversity, and human health. Crops, animals, and people may not adapt equally well to a sudden reduction in solar energy.
• Risk of sudden abolition ("termination shock")If geoengineering were to be abruptly halted once implemented, the rise in temperatures would be extremely rapid, exceeding any capacity for biological or social adaptation.
• Geopolitical consequences and equityWho controls and decides when to implement or deactivate these technologies? The regions least responsible for global warming (Global South, indigenous communities, coastal areas) could be the most affected in the event of negative side effects.
• Difficulty in distinguishing the effects of geoengineering from natural climate changeThis complicates governance and the global response.
• Ethical and moral pressuresFor many, geoengineering is just a band-aid solution. It does not address the underlying cause. (emissions), but only one of its symptoms (temperature). Furthermore, it can decrease public and political pressure to make real progress in reducing emissions.

The political risk is very high.The possibility that a single country, private actor, or billionaire could implement it unilaterally raises genuine international fears, as any large-scale experiment could trigger tensions, lawsuits, or even direct conflicts.

Who is behind the rise of solar geoengineering?

Private and public funders are investing heavily in the development of these technologiesMajor figures in the technology sector such as Bill Gates, Mark Zuckerberg and international investment funds have financed experiments, while institutions such as NOAA and NASA participate in climate research and modeling.
Some solar geoengineering companies already offer "cooling credits" to offset, in theory, their own emissions by financing specific projects.

Is solar geoengineering legal? The international framework

The legal framework is ambiguous and uneven.The United Nations Convention on Biological Diversity (CBD) has imposed a global moratorium on geoengineering, except for small-scale scientific experiments in controlled environments. The United States, however, is not bound by this agreement.

In the absence of clear global governance, concerns are growing about who will assume risks and responsibilities.Attempts to release aerosols or modify atmospheric processes could be subject to local environmental laws when they involve spills or emissions, but loopholes and a lack of specific regulation abound.

Opposition to solar geoengineering is growing across many segments of civil society and in the Global South. More than 500 academics and all African countries have called for a Non-Use Agreement. Indigenous communities have successfully blocked experiments planned for their traditional territories, citing a lack of consultation and risks to biodiversity and their ways of life. There is also pressure for inclusive, transparent, and human rights-based governance.

And what about 'chemtrails'?

A popular (and unfounded) belief is that commercial airplanes are already acting as vectors for solar geoengineering, secretly releasing aerosols. However, there is no confirmed evidence that this is happening.What airplanes do cause, through their routes and emissions, are condensation clouds that actually amplify warming by trapping heat near the Earth's surface.

Solar geoengineering: solution or distraction?

For a significant part of the scientific community and social groups concerned about the climate, Solar geoengineering should not be used as an excuse for failing to address the causes of climate change.Such intervention could divert attention and resources needed to promote renewable energy, transform agriculture, and truly reduce the use of fossil fuels.

The most recent studies agree: solar geoengineering could, at best, be an emergency tool, a risky "plan B" of last resort if warming gets out of control.But in no case is it a substitute for decarbonization or the ecological transition.

As we have seen, solar geoengineering compiles technological proposals that are as imaginative as they are controversial, capable of giving the planet a temporary respite but fraught with far-reaching scientific, social and political risks. Their future will depend on humanity's ability to combine innovationresponsibility and truly fair and transparent global governance.

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