Marine Cloud Brightening (MCB)

Dec 26, 2023

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Table of contents

Context (TH): Marine cloud brightening (MCB) is a geoengineering technique that produces brighter and whiter low marine clouds.

Such clouds reflect sunlight away from the ocean’s surface and protect corals from bleaching.

How is a Cloud Brightened?

A warm cloud (as opposed to an ice cloud) is a collection of small water droplets floating in the air.
A cloud with numerous small droplets appears brighter than one with fewer large droplets, regardless of their total water content.
Each droplet is formed by condensation of water vapour around a nucleus.
The nucleus can be any tiny particle suspended in air.
In the lower atmosphere, there are thousands of tiny airborne particles called “aerosols”.
In very clean maritime air, aerosols available are mainly sulphates and sea salt crystals.
They are generally fewer in number, resulting in the formation of clouds with large droplets.
So, to boost marine aerosols, large volumes of tiny seawater droplets are sprayed into the air.
As the tiny seawater droplets evaporate, they leave behind sea salt. These additional sea salts, when incorporated into a cloud, brighten the cloud.

Aerosols can be:
- Natural such as dust, sea salt, pollen, ash, and sulphates
- Human-made such as from burning fossil fuels or vegetation, vehicle exhaust, & aerosol spray cans.