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The clouds over the Pacific Ocean just became the most contested real estate on Earth.
ISS photograph, northwestern Pacific, 2013. NASA public domain.

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What Is Marine Cloud Brightening
Marine cloud brightening (MCB) is a form of solar geoengineering that works by spraying fine sea salt aerosols less than 2 km above the ocean surface. The particles seed low stratocumulus clouds, creating more numerous and smaller droplets, which makes the clouds whiter and more reflective. More sunlight bounces back to space. Less heat reaches the ocean below. In theory, a sustained MCB program over the eastern Pacific could reduce global mean surface temperatures measurably within years, at a fraction of the cost of reducing emissions. In practice, the 2026 research shows the side effects may be planet-scale.


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100 hrs

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How It Would Work
The leading design uses a fleet of automated ships that spray seawater into the marine boundary layer. Each vessel produces a continuous plume of tiny salt crystals, each less than 0.2 micrometres across. The spray enters existing low clouds and boosts their droplet count. Field trials have already been conducted off the California coast, and in 2024 a small-scale Australian experiment provided inadvertent real-world data confirming the cloud-response models. Scaling to a meaningful climate effect would require hundreds of vessels operating continuously across the subtropical eastern Pacific, coordinated internationally with no existing treaty framework.


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How MCB Suppresses El Nino (the chain)
[x] Sea salt aerosols seed low stratocumulus clouds over the subtropical eastern Pacific
[x] Clouds become brighter and more reflective, reducing sea surface temperature below
[x] Cooler surface water strengthens the east-to-west trade winds
[x] Stronger trade winds push warm water further west, starving the El Nino feedback loop
[x] ENSO variability falls by up to 61 percent in climate model simulations
[ ] Real-world deployment and governance framework: does not yet exist

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Unintended consequences. Suppressing El Nino by 61 percent would reshape monsoon patterns across South Asia, alter drought cycles in sub-Saharan Africa, and shift the path of Atlantic hurricanes. Regions that rely on El Nino-driven rainfall for agriculture could face multi-year droughts with no warning and no compensation mechanism. The 2026 Earth's Future study explicitly warns that regional benefits and harms would not be distributed equally.


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:LINK
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025EF006522
Earth's Future: MCB suppresses the El Nino cycle (2025/2026)

:LINK
https://www.sciencedaily.com/releases/2026/06/260626030448.htm
ScienceDaily: A popular climate fix could accidentally trigger massive weather changes