What is marine cloudbrightening?

MCB is a technique to brighten marine clouds. Brighter (whiter) marine clouds mirror more sunlight back into space than dark ones. Therefore, if we could brighten marine clouds on a global scale just a little, we could cool the Earth by up to 1 C, refreeze the Arctic which is heating up 3 to 5 times faster than the rest of the planet, and roll back climate change, at least temporarily. By cooling down the areas below the clouds, MCB could bring relief to ecosystems under heat stress, such as the Great Barrier Reef.

MCB is potentially our most effective way to adapt to global warming.

Cloud brightening happens because smaller water droplets reflect more light than bigger water droplets: the Twomey effect. This is visualized in the image below: the jar on the right contains smaller glass spheres than the one on the left and therefore appears brighter.

Now cloud water droplets grow on tiny dust particles: aerosols. When aerosols act as nucleation sites for droplet formation, they are called Cloud Condensation Nuclei (CCNs). The more CCNs in the clouds, the larger the number of water droplets growing on them. This larger number of droplets will compete for the available water vapour, and thus the droplets will remain smaller than in the case with only a few CCNs.

This larger number of smaller droplets will brighten the clouds. Whiter clouds reflect more solar radiation back into space and therefore provide cooling!

Satellite images of ships’ exhausts in which soot acts as CCNs drive home the point. Even under a cloud deck, these exhausts lead to bright lines in satellite images (see the figure below). Bright! Means more reflected light! But soot is hardly an attractive CCN. What about sea salt nano particles generated at sea, as suggested by Latham in 1990? The concept of Marine Cloud Brightening was born.

How doesMCB work?

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What are thebenefits of MCB?

The localised approach allows for greater control and minimises the risk of unintended consequences both at a local level and on a global scale.

Calculations show that the annual amount of targeted sea salt CCNs necessary to obtain effective cooling is less than what a vigorous North Atlantic gale produces in a couple of days!

MCB only happens when marine clouds are seeded with sea salt CCNs. If seeding is switched off, MCB will not last for more than a few days i.e., the lifetime of marine clouds. Its effects are therefore fully reversible Consequently, MCB’s effects are fully reversible within a matter of days.

Apart from the stratocumulus cloud carpets mentioned above, MCB can target specific regions or vulnerable ecosystems that are under severe heat stress. These include coral reefs, overheating sea currents, summer cloud formations over the Arctic, coastal areas etc… Used for these purposes, MCB provides both local relief and global cooling all at once.

Hurricane formation is intensified by elevated sea-surface temperature. MCB could provide local sea surface cooling in hurricane-prone areas in order to mitigate the intensity of hurricanes (typhoons). Again, in such case, MCB provides both local relief and global cooling all at once.

A growing body of scientists fears that we have already breached several tipping points, amongst other the melting of the Greenland ice cap and the extinction of coral reefs. If such breaches are left to progress, they become unstoppable and irreversible due climate change’s profuse and powerful positive feedback loops. In other words: once tipping points are breached, there is no way back. Tipping points are the scariest aspect of climate change. By providing global cooling of up to 1C, MCB puts a temporary break on such catastrophic breaches and keeps tipping points at bay.

MCB benefits from on an extensive understanding of cloud physics and marine ecosystems. Proof of Concept could be obtained latest by the summer of 2026 and large-scale deployment could start by the end of the decade. This could be just in time to avoid the worst of global warming and keep tipping points temporarily at bay.

A. MCB is budgeted to cost abt usd 10 bio in the deployment phase, and yearly maintenance is estimated at usd 1-2 bio/year. Global warming today – let alone tomorrow - already costs in the order of usd 200 bio/yr, not factoring in human suffering. Unfairly, societies which emit the least GHGs, such as in the Sahel, in many areas around the Equator and in most of the Global South are at the greatest risk of global warming. MCB’s global cooling would greatly relieve their distress.

B. By cooling the planet globally by up to 1C, and therefore refreezing the Arctic, MCB buys humanity enough time - maybe 30-40 years – to get rid of anthropogenic GHG-emissions and massively remove GHGs from the atmosphere. MCB enables the 3Rs of the climate repair deal: Reduce, Remove, Refreeze.

What are thechallenges of MCB?

With RAF-funds, universities are cracking the many challenges of MCB!

What has RAF-funded researchfunded so far?

MCB is a technique to brighten marine clouds. Brighter (whiter) marine clouds mirror more sunlight back into space than dark ones. Therefore, if we could brighten marine clouds on a globalasd

MCB testing to save the Great Barrier Reef

a. The Southern Cross University has invited CCR to help assess its MCB field trials focused on protecting the Great Barrier Reef from coral bleaching.

b. The first series of tests provided encouraging results, indicating that the practical effectiveness of MCB might even perform better than earlier models predicted.

CCR research into spraying devices

CCR is developing no less than four novel techniques to produce the desired sprays;
One such device – YYY - is ready to be upscaled. This comes on top of the spraying techniques being developed in the USA by XXX

TUDCI research into CCNs

TUDCI is incorporating CCN distributions provided by CCR into its large eddy cloud models to examine if the hoped-for Twomey effect can be modelled.

TUDCI research into MCB side-effects

a. TUDCI is investigating potential side-effects of MCB. One key claim is that MCB won't significantly change precipitation patterns, but is this really the case? The science behind MCB’s side-effects is still not well understood - but not for long!

Summer of 2026

CCR and TUDCI are ever more confident that they can deliver MCB Proof of Concept by the summer of 2026, backed-up by reviewed computer modelling and field trials.

It’s time to Refreezethe Arctic

A nascent body of fact-based, peer reviewed science allows us to have high hopes for MCB.

MCB promises enough cooling to temporarily halt the loss of the Arctic ice cap, and it could be available within a short timeframe. Refreezing the Arctic will give us a fair chance to keep tipping points at bay. MCB is potentially our most effective way to adapt to global warming.

However, the window of opportunity to deploy MCB at scale is closing fast. Research into MCB must be fast-tracked with the highest possible priority, whilst society debates its merits transparently and in good faith. The RAF is proud to act as a catalyst in the delivery of MCB Proof of Concept.

More Ice, More Life!


Awaiting references from RAF

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