What on Earth Is Solar Geoengineering?

Imagine you are standing outside on a blazing summer afternoon. Now imagine someone holds a giant, semi-transparent umbrella between you and the sun. You feel cooler almost instantly, not because the temperature itself dropped, but because less sunlight is hitting you directly. Solar geoengineering is essentially that idea, applied to the entire planet.

The formal definition is: deliberately altering the amount of sunlight that reaches and is absorbed by the Earth’s surface in order to slow down or reverse global warming. Scientists call it Solar Radiation Management (SRM). While it sounds futuristic and a little alarming, the underlying physics is actually borrowed straight from nature.

The Four Main Approaches

Scientists have proposed several different ways to achieve solar cooling. Here is a plain-English breakdown of each:

Why Is Anyone Even Considering This?

The honest answer is: desperation. Global carbon emissions are not falling fast enough to keep warming below 1.5°C — the threshold scientists say would prevent the most catastrophic climate impacts. The Intergovernmental Panel on Climate Change (IPCC) now lists stratospheric aerosol injection as ‘the most-researched solar radiation modification method’ and concludes it could, in principle, limit warming below 1.5°C if deployed correctly.

Proponents are careful to say solar geoengineering is not a silver bullet and not a substitute for cutting emissions. They frame it as a potential ’emergency brake’ — a way to buy time while the world transitions away from fossil fuels. Critics argue it is a dangerous distraction that gives polluters an excuse to keep burning.

Also Read: What Does The Record Rise In CO₂ Levels Mean For Global Warming? Scientists Explain

How Did Bill Gates Get Involved?

The involvement of the world’s most well-known tech billionaire in atmospheric science is an unusual story. It starts not with a grand plan to dim the sun, but with a quiet research fund set up nearly two decades ago.

In 2007, Bill Gates, through his personal philanthropic activity, began financing the Fund for Innovative Climate and Energy Research (FICER), a multi-million dollar fund managed by two prominent climate scientists: Professor David Keith (then at the University of Calgary, later at Harvard) and Dr. Ken Caldeira (at the Carnegie Institution for Science). FICER was designed to explore outside-the-box climate interventions, and solar geoengineering was a central topic of interest.

What Is FICER?

FICER stands for Fund for Innovative Climate and Energy Research. It is not a public fund or government grant; it is essentially a private research kitty funded by Gates’ personal wealth. Between 2007 and roughly 2018, it distributed millions of dollars in grants to climate scientists studying solar radiation management, carbon capture, and related fields. Crucially, FICER operated with very little public transparency, which later drew criticism from governance experts.

How Much Money Has Gates Invested?

Direct figures from Gates’ personal geoengineering spending are difficult to pin down because much of it flows through intermediary programs.

However, reporting and academic sources indicate:

It is important to note what Gates’ funding was actually for. The research he financed was largely about understanding the risks and mechanics of solar geoengineering — not deploying it. In his own words and through his foundation’s positioning, Gates has consistently described this as ‘learning enough so that we are prepared to make informed decisions,’ not advocating for immediate geoengineering of the atmosphere.

⚠️ Context Matters

Much of the internet controversy around Gates and ‘blocking the sun’ conflates two different things:

(1) funding research to understand whether geoengineering is safe and effective, and

(2) actually doing geoengineering.

The SCoPEx project, the main experiment linked to Gates, was specifically a data-collection exercise aimed at refining computer models. It was never a plan to alter the planet’s climate. The project was, in fact, cancelled before a single outdoor experiment was completed.

Also Read: Climate Geoengineering: From Research To Public Debates

SCoPEx: The Experiment That Never Happened

What Does SCoPEx Stand For?

SCoPEx stands for Stratospheric Controlled Perturbation Experiment. It was a Harvard University project, with its principal investigators being Professor Frank Keutsch and Professor David Keith. It was proposed around 2015 and spent several years in planning and community consultation before being officially cancelled in March 2024.

What Was the Actual Plan?

Here is the actual, rather modest experiment that generated enormous global controversy:

Why Was It Cancelled?

The opposition to SCoPEx came from multiple directions simultaneously. In 2021, when the team attempted to conduct a test balloon flight in Kiruna, Sweden, the Swedish Space Corporation — which was providing the launch facility — cancelled it after pressure from the Saami Council (representing Indigenous Sami peoples of Arctic Scandinavia) and dozens of global environmental organisations. The groups argued that even a small experiment could normalise geoengineering and create a ‘slippery slope’ toward large-scale deployment without proper democratic consent.

The Harvard advisory committee for SCoPEx also raised concerns about the adequacy of community engagement processes. After years of repeated delays and mounting criticism, Professor Frank Keutsch — the principal investigator — announced in August 2023 that he was suspending the work. Harvard made the cancellation official in March 2024.

The Geoengineering Timeline (2007 – 2026)

What Is Actually Happening in the World Today?

Despite the controversy, solar geoengineering research has accelerated sharply since 2023. Here is a region-by-region breakdown of what is actually taking place on our planet right now — from responsible university programs to controversial commercial operations.

Australia — Great Barrier Reef Marine Cloud Brightening

Australia has the most systematic government-supported outdoor MCB program in the world, motivated by the bleaching crisis devastating the Great Barrier Reef. The Australian Institute of Marine Science (AIMS), in partnership with Southern Cross University, has been conducting trials since 2020 near Townsville, Queensland. In 2023 trials moved to Heron Reef off Gladstone, and in 2024 to Gouda Reef — 500 km off the Queensland coast.

These trials use research vessels and drones to spray fine sea mist, measure aerosol behaviour, and study cloud formation. A key milestone reported in early 2025: sea-salt aerosols successfully reached cloud base — a critical proof-of-concept step. The Australian government has also created a dedicated Cooling & Shading subprogram to research MCB and ‘marine fogging.’ Further 2025 trials are underway, but details remain unpublished.

📍 Great Barrier Reef MCB — Why Here?

The Great Barrier Reef has experienced mass bleaching events in 2016, 2017, 2020, 2022, and 2024 — caused by elevated ocean temperatures. MCB is being researched as a way to locally cool reef waters by just 0.5–1°C during critical summer months, potentially preventing bleaching. This is a very different application to global SAI — it’s about protecting a specific, irreplaceable ecosystem.

United States — USS Hornet MCB & NOAA Research

In April 2024, University of Washington scientists tested a custom Marine Cloud Brightening spray machine aboard the decommissioned USS Hornet aircraft carrier, moored on San Francisco Bay in Alameda, California. The machine — developed over a decade — uses 60 ultra-fine nozzles to produce saltwater particles small enough to seed clouds. The test was the first outdoor trial for the university’s Marine Cloud Brightening Research Program (MCBP).

The Alameda city council subsequently voted to shut down the experiment in June 2024, criticising the team’s lack of public transparency. The MCBP has reportedly been planning a much larger offshore trial — potentially covering an area larger than the island of Puerto Rico — but details remain confidential. The EPA separately confirmed that as of mid-2025, it is aware of only one private actor conducting active geoengineering: Make Sunsets.

At the federal level, NOAA has been the only US agency receiving explicit funding to study SRM, conducting atmospheric modelling, stratospheric observations, and lab research since 2020.

United Kingdom — ARIA’s £56.8 Million Research Programme

The UK has emerged as one of the most aggressive government backers of solar geoengineering research. In 2024, the Advanced Research and Invention Agency (ARIA) — Britain’s answer to DARPA — announced approximately £56.8 million (roughly $75 million USD) for a programme to research climate-cooling technologies, explicitly including small outdoor field experiments. An additional £10 million from UK Research and Innovation’s NERC funds four new modelling research projects under a 5-year programme called ‘Modelling Environmental Responses to Solar Radiation Management.’

By early 2025, UK outdoor trials were described as imminent, with government-backed experiments expected to include drone and ship-based seawater spray tests for marine cloud brightening. The Guardian reported in April 2025 that outdoor trials could begin ‘within weeks.’ This makes the UK among the world’s leading funders of geoengineering research per capita.

Make Sunsets — The Rogue Commercial Operator

Make Sunsets is a US-based for-profit startup that has become the most controversial actor in the geoengineering space. Founded in 2022, the company began launching weather balloons filled with sulfur dioxide (SO2) into the stratosphere and selling ‘cooling credits’ to buyers who want to offset their carbon footprint. No formal scientific oversight. No academic peer review. No government authorisation.

Their first launch was conducted in Mexico in late 2022. The Mexican government responded in January 2023 by announcing plans to ban all outdoor solar geoengineering experiments — legislation that had not been finalised as of mid-2025. Make Sunsets has since launched over 120 SO2-filled balloons and reports releasing approximately 0.1 tonnes of SO2 into the stratosphere as of May 2025. The US EPA, under Section 114 of the Clean Air Act, sent a formal information demand to the company in April 2025. The EPA is now assessing whether existing legal powers are sufficient to stop or regulate such commercial activity.

Norway — The Navigate Project

Launched in April 2025, the Navigate project is a collaborative Norwegian initiative involving researchers from NORCE, BCCR (Bjerknes Centre for Climate Research), CICERO (Centre for International Climate Research), and the Norwegian Meteorological Institute. The project focuses on understanding the climate risks, trade-offs, and governance implications of solar radiation management. Norway’s involvement marks an expansion of European scientific engagement with geoengineering research beyond the UK.

How Would Stratospheric Aerosol Injection Actually Work?

Let us break down the physics of the most widely researched method — Stratospheric Aerosol Injection (SAI) — in plain English.

Benefits vs. Risks: A Balanced View

Solar geoengineering is perhaps the most divisive topic in climate science. Here is a fair, evidence-based breakdown of the strongest arguments on both sides:

The India Question

India is a particularly important case study for SAI risk. About 600 million people in India depend directly on the southwest monsoon for their agricultural livelihoods. Multiple climate models show that large-scale SAI could disrupt monsoon rainfall patterns across South Asia. India has formally opposed geoengineering through the Convention on Biological Diversity, yet remains relatively quiet in international governance forums. Researchers and policymakers in South Asia have called for far greater inclusion in any global geoengineering governance framework.

Governance: The Wild West of Atmospheric Science

Perhaps the most alarming aspect of solar geoengineering is not the science — it is the total absence of adequate global governance. As of early 2026, there is no binding international treaty, no UN framework, and no global enforcement mechanism governing who can experiment with — or deploy — solar geoengineering technologies.

What Governance Exists Today?

The governance vacuum means that a wealthy nation, a tech billionaire, or even a small startup could theoretically begin spraying the stratosphere with aerosols without any international check. The geopolitical risks are staggering: if the US were to deploy SAI and it disrupted India’s monsoon, would that be considered an act of aggression? These questions have no international legal answers yet.

The Funding Landscape (2024–2026)

Solar geoengineering research funding has reached record levels in 2024–2026. Here is a snapshot of major recent commitments:

The funding picture reveals a critical shift: governments — especially the UK — are now the dominant drivers of geoengineering research, replacing the earlier model where private billionaire philanthropy (Gates, others) was the primary engine. This brings both more resources and more democratic accountability to the field.

The Bottom Line

Solar geoengineering sits at the uncomfortable intersection of climate desperation, technological optimism, geopolitical power, and ethical uncertainty. Here is the state of play as of early 2026:

The question is no longer whether solar geoengineering will be researched — that is already happening. The question is whether humanity can develop it wisely enough, and govern it fairly enough, to avoid exchanging one planetary crisis for another. The thermostat of Earth’s climate is being considered for human control. The world needs to decide, urgently and collectively, who gets their hands on it.

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