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Can we cool the Earth? Cambridge scientists to lead research
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Scientists are exploring ways to cool the Earth alongside vital emissions reduction.
Rapidly reducing greenhouse gas emissions is essential to reduce global warming and limit the associated effects of climate change. However, many are concerned that current global pledges to decarbonise will not prevent the planet from exceeding 1.5C above pre-industrial levels, the limit set out in the Paris Agreement at COP21.
There are various Earth cooling approaches that could prevent catastrophic temperature increases and protect vulnerable regions like the Arctic, as society continues to decarbonise. Although the ideas are well-studied through modelling, there has yet to be significant outdoor experimentation to test real-world impacts.
Scientists from the University of Cambridge are leading teams to undertake research on methods to cool the Earth. Through controlled, small-scale outdoor experiments, they will assess the potential to rethicken Arctic sea ice and whether there are natural, non-toxic materials that could be suitable for stratospheric aerosol injection. This will be done without releasing materials into the atmosphere.
The research is set to be funded by the Advanced Research and Invention Agency (ARIA), a UK research and development funding agency, as part of its Exploring Climate Cooling programme.
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Prof Hugh Hunt and Dr Shaun Fitzgerald lead the Centre for Climate Repair at the University of Cambridge. Between them, they are supporting four new projects to be funded by ARIA.
A planet on ice
“There is a growing need for innovative solutions to combat the effects of climate change alongside emissions reduction,” says Dr Shaun Fitzgerald of the Centre for Climate Repair, who is leading one of the teams.
“While emissions reduction is essential, it may not be enough to avoid catastrophic warming. By researching potential climate cooling approaches that are scalable, this programme offers a timely opportunity to build a knowledge-base to better understand approaches that could help stabilise Earth’s climate and protect vulnerable ecosystems and communities.”
Dr Fitzgerald’s team will explore the feasibility of thickening sea ice in the Arctic to mitigate the loss of sea ice coverage and potentially cool the region.
“We've been seeing year on year reductions in the areal extent and volume of sea ice,” says Fitzgerald. "This has a significant impact on people who live in the Arctic. It’s affecting how they move around, and it is changing the migration patterns of wildlife such as caribou, which in turn also affects the livelihoods of indigenous people.”
The loss of sea ice also has a major impact on the global heat balance in the summer. Instead of the Arctic being covered with a white reflective sheet of ice, more of it is now a dark blue ocean. The dark ocean absorbs a large proportion of the incoming radiation in the summer, whereas previously the white sea ice reflected it.
“Working with people in the high Arctic, we want to investigate ways to potentially reduce the rate of loss and potentially even rebuild some of the sea ice as a temporary measure until we fix the underlying problem, which is our emissions of greenhouse gases,” said Fitzgerald.
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Some of Dr Fitzgerald's team conducted experiments in Canada earlier this year, before receiving ARIA funding. Early results showed ice growth of about half a metre.
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Retrieving equipment from a day of measuring. Image credit to Real Ice.
The team includes researchers from the universities of Cambridge, Manchester, Washington, and Arizona State, University College London, and teams from Real Ice and Arctic Reflections.
Together with members of local communities, they will conduct controlled, small-scale experiments in Canada across three winter seasons (2025-26 to 2027-28). The process involves pumping seawater from beneath existing ice and spreading it on top, where the frigid air freezes it quickly, creating thicker ice patches.
It will build on modelling and laboratory research, as well as environmental assessments and community engagement. By gathering real-world data, they aim to assess whether the intervention warrants further investigation.
Looking up
Prof Hugh Hunt, from the Department of Engineering at the University of Cambridge, is leading a project to advance the field of stratospheric aerosol injection (SAI).
SAI is based on the idea that aerosols in the stratosphere can reflect solar radiation and limit the amount that reaches the Earth. It is a widely discussed method, but the most commonly proposed materials (sulphates) carry significant hazards in this context. Hunt’s team will study the properties and behaviour of other, natural materials.
As part of the study, specifically adapted weather balloons will carry tiny samples of potential materials into the stratosphere for varied exposure periods. No materials will be released; the recovered samples will effectively reveal how stratospheric conditions affect their properties over time.
Testing this foundational science will help the scientists to better understand the potential impacts of SAI and inform any future research.
Working together
There are a number of other projects being funded in the new programme, led by universities around the world.
Dr Fitzgerald and Prof 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.
These projects are just part of a new programme funded by the Advanced Research and Invention Agency (ARIA), a UK research and development funding agency*.
It is designed to explore a range of potential approaches to climate cooling; with a breadth of research, society can be better equipped to make informed decisions on which, if any, should be warrant further research. All projects will be guided by ARIA’s principles for governance, oversight, and transparency.
“These are vital to ensure that research is carried out in a responsible, ethical manner with full accountability,” says Fitzgerald. “We want to ensure that any findings are credible and that the work involves local communities and stakeholders.”
In the programme thesis, ARIA said: “Our objective is that the information gathered by this programme will allow for more definitive assessments on whether one or more of the approaches examined may one day be used responsibly and ethically to delay or avert the onset of temperature-induced climate tipping points.”
Earth cooling approaches are not intended to replace emissions reduction to tackle climate change but, if they are found to be viable, they could provide a pathway to avert the worst consequences of a rapidly warming world.
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At a recent event for the public, Prof Hugh Hunt spoke on the dangers facing the Arctic and the world as a result of global warming.
You can read more about the projects on the Exploring Climate Cooling webpage. Find out more about our other research at Centre for Climate Repair. Images from the Arctic belong to our partners Real Ice.
*All the projects are subject to final contract negotiation.
Looking forward
From 26th-28th June, we're hosting a conference on Arctic Repair - all about solutions to protect the region from global warming. Join us in Cambridge, UK, for an opportunity to discuss this research and other big ideas. Visit ArcticRepair2025.com to register.
