
Refreeze
The loss of Arctic sea ice is a global issue. The bright white ice reflects solar radiation back into space, cooling the planet. As it gets warmer, the reflective ice is replaced by dark ocean water that absorbs the sun’s rays. It’s a doom loop - global warming accelerates melting, and the melting accelerates global warming.
Over the past few decades, the Arctic has experienced unprecedented rates of warming, nearly three times the global average, a phenomenon known as Arctic amplification. This rapid warming has led to significant reductions in sea ice extent and thickness, with dire consequences not only for the Arctic ecosystem but for global climate stability.
Halting or reversing Arctic sea ice loss could be a global “safety belt” that would inhibit further ocean warming and stop the catastrophic decline in the delicate ecosystems that are unique to this region. Minimising sea-ice retreat could also protect the rights and livelihoods of the indigenous peoples and local communities in the Arctic in the face of increased shipping, tourism and extraction, and support geopolitical security and defence globally.
At the Centre for Climate Repair, we are exploring innovative solutions to preserve Arctic sea ice.
Marine Cloud Brightening (MCB):
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. The CCR is researching the performance and suitability of a variety of spraying methods including:
- 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.
- 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.
- 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.
- 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.
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).

Read more about the need for MCB research in an article by Prof Hugh Hunt here.

Stratospheric Aerosol Injection (SAI):
SAI is more established as a potential way to reflect a portion of incoming solar radiation, but field experiments through SPICE and SCOPEX faced challenges.
The Centre for Climate Repair supports further research in this area and recognises the expertise which already exists in the field in other leading institutions such as Harvard, Exeter and Chicago, with whom it is in regular contact.
CCR research effort in Cambridge’s Department of Geography focusses on establishing paleoclimate records, and investigating the Atlantic Meridional Overturning Circulation, as well as where large cluster volcanoes may have had an impact on the climate.
Sea Ice Thickening
Sea ice forms naturally by water freezing on the bottom of existing ice which floats on the ocean’s surface, the latent heat of freezing must be conducted through the ice and then transferred to the cold Arctic air or radiated into space. As the ice grows it becomes a thicker insulating layer between the cold Arctic air above the ice and the water below it, so the rate of freezing reduces. Any snow on the ice’s surface is an even better insulator and further slows the rate of ice growth. The Centre for Climate Repair is researching two techniques to thicken sea ice by pumping seawater through the ice and onto the surface during the Arctic winter which we call Surface Thickening and Snow Flooding:
- Surface Thickening aims to increase the sea ice thickness directly when there is no snow by pumping seawater onto the surface, so it is directly exposed to the cooling and thickens the ice from above.
- Snow Flooding aims to fill the air voids in snow that make it so insulating with seawater thereby consolidating the snow into solid ice which is less insulating so there is more natural freezing at the ice’s base.
The research happening in Cambridge focuses on modelling and lab experiments in a cold room to investigate the two techniques. It aims to answer core questions regarding the freezing process, particularly the increase in ice thickness that can be achieved and the behaviour of brine in the sea ice. This project is led by Dr Shaun Fitzgerald in the Department of Engineering and supported by Professor Grae Worster in the Department of Applied Mathematics and Theoretical Physics.
We are working in collaboration with Real Ice, who are conducting field experiments in Cambridge Bay, Nunavut, Canada. Their field data is providing invaluable insights and they are not only engaging but directly involving Inuit in the project.

New Scientist shared promising results from our research here. Real Ice were featured on PBS Terra; watch the 10-minute video on YouTube.

Sea curtains:
Sea curtains stem conceptually from work originally proposed for the Thames Barrier in London, whereby a fabric curtain is placed in the water with the bottom tethered to the ocean floor and with floats attached to the top of the curtain. As the floats are inflated, the curtain rises and creates a barrier to the basal current, thereby reducing the rate of ingress of warm saline water towards the glacier. This may be critical to tackling the accelerated erosion of glaciers due to ingress of warm saline water.
Governance and society:
Applying any approach at scale to Refreeze or Climate Repair more generally means working with affected communities, governments, and world leaders on policy and social acceptability. Impactful research requires participation from industry to scale-up, permission from international bodies to enable deployment at scale, and support from the wider public. Furthermore, consideration of effects in the Arctic on the rest of the world are important since what goes on in the Artic as far as the climate is concerned does indeed affect other climate systems.
CCR works with a wide range of stakeholders as we try to establish the appropriate governance systems and structures for both research and any subsequent decisions on potential deployment.
