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Marine Cloud Brightening
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Image by Brendan Kelaher for Southern Cross University
Marine Cloud Brightening (MCB) is a solar radiation management strategy aimed at increasing the amount of incoming solar radiation which is reflected back into space from clouds over the oceans. Increasing cloud albedo is achieved by increasing the number of cloud condensation nuclei (CCN) present within the clouds which leads to smaller cloud droplets and a whiter, brighter, appearance - a phenomenon known as the Twomey effect. MCB involves spraying small seawater droplets into the atmosphere which then evaporate, and the resulting salt crystals act as new CCNs when they reach the cloud boundary layer.
Much of the work at CCR is aimed at developing efficient spraying techniques that can generate large quantities of submicron seawater droplets for the purpose of MCB. We are exploring a range of potential methods including: superheated sprayers with converging and diverging nozzles; Rayleigh break-up of water with and without vibration; electrosprays; and different configurations of devices which form bubbles. Each of these methods have different characteristics which need to be considered as part of the evaluation to determine which method(s) are potentially applicable to MCB.
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The idea
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Electrospraying involves the application of high voltage to a liquid, as opposed to high pressure, to emit submicron jets from narrow capillaries which disintegrate into streams of droplets. Researcher Jake Chapman is the lead on this method.
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Bubble-bursting atomisation is inspired by natural sea spray and uses low-pressure air jets to simultaneously form and burst seawater bubbles. Researcher Yashasvi Raj is the lead on this method.
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Rayleigh jet disintegration from micron and sub-micron sized holes in silicon, for the purpose of MCB, is being investigated by researcher Jake Chapman, with assistance and technology from Medspray B.V.
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Superheated atomisation involves spraying seawater at very high temperatures and pressures, through a nozzle of precise geometry, to achieve a fine mist of droplets. Researcher Edmund Reardon is the lead on this method; he is investigating nozzle geometries that induce shock waves at the throat that break up large droplets (> 1 um) which are constricted by the diverging section of the nozzle.
The MCB research is led by Professor Hugh Hunt in the Department of Engineering. The research is undertaken in collaboration with TU Delft under the leadership of Professor Herman Russchenburg (modelling and cloud physics).
Our work
Starting 2025: REFLECT project
Dr Shaun Fitzgerald and Prof Hugh Hunt are supporting the REFLECT project led by the University of Manchester in collaboration with the National Centre for Atmospheric Sciences (NCAS).
The team will investigate marine cloud and sky brightening techniques (MCB/MSB) involving spraying seawater to create sea salt droplets above the ocean or coastal environments. These droplets increase the reflectivity of the atmosphere and clouds, preventing some solar radiation from reaching the Earth’s surface in that area.
They will undertake computer modelling, build bespoke sprayers based on the modelling results, and conduct indoor tests; during this time, they will begin collaborative engagement with local communities to co-design potential future outdoor experiments.
Resources
In the news
The Manmade Clouds That Could Help Save the Great Barrier Reef
MCB research by our collaborators at Southern Cross University featured in the New York Times.
Watch: Can science save the Great Barrier Reef?
Dante McGrath interviewed by the University of Cambridge.
Our collaborators
