Climate intervention to reflect sunlight back into space is presented at symposium
A climate intervention that could temporarily hold back global warming by reflecting sunlight back into space is the subject of a St John’s PhD student’s research.
Jake Chapman presented his work on marine cloud brightening at a symposium at the College for St John’s postgraduate research last month.
His PhD is focused on developing seawater aerosol generators that can make clouds whiter to reflect more solar radiation away from the earth.
He is working on two energy-efficient spray methods that can then be tested in an area over the Great Barrier Reef in Australia, which is at risk from rising temperatures.
Jake, who is working at the Centre for Climate Repair in Cambridge, says: “Human-induced global warming rates are at their highest historical level and current world action on tackling climate change is insufficient to prevent devastating regional and global consequences.
“We are now at a point where reducing emissions alone is no longer enough to avoid serious ecological damage. Marine cloud brightening (MCB) is a proposed solar radiation management strategy that may have the potential to provide temporary local or global cooling with the aim to protect and restore the most vulnerable ecosystems while deep and rapid emissions reductions are made.”
Earlier this year, the World Meteorological Organisation confirmed that 2024 was the hottest year on record, exceeding the 1.5˚C target set in the 2015 Paris Agreement. Jake explains that this temperature represents a tipping point for many of the world’s ecosystems, including ice shelves, tropical reefs, boreal permafrost and the Arctic.
We’re in a quite tragic situation now, where reducing emissions alone is no longer enough to prevent some of the worst effects of climate change
Marine cloud brightening is one of the climate interventions being investigated by the Centre for Climate Repair that could help to pause global warming for long enough to allow countries to reduce carbon emissions that are driving climate change.
Jake says: “Marine cloud brightening is the idea of making clouds over the oceans more reflective, whiter and brighter. Clouds are naturally reflective of incoming solar radiation, whereas the ocean is dark, and so it absorbs more solar radiation. So if we can make clouds even more reflective, then we can reflect more sunlight back up into space, and it will provide a temporary cooling effect within the atmosphere.
“We’re in a quite tragic situation now, where reducing emissions alone is no longer enough to prevent some of the worst effects of climate change. We’re predicting we will lose the Arctic by 2035, so we have 10 years left. We will lose between 70 to 90 percent of all coral reefs if we exceed 1.5 degrees of warming. Last year was the first year on record where we exceeded 1.5 degrees of warming. We’re already there. Currently the most optimistic scenario, if all countries meet their net zero target, is that we will limit warming to around two degrees by the end of century, which would be catastrophic to a lot of the most vulnerable ecosystems and societies. It will lead to more crop failure, more extreme weather, more displacement of people.
“Interventions like marine cloud brightening may be our only option to protect places like the Arctic or the coral reefs in the short term, while we start to get emissions down so they can buy us some more time. It could be used to lessen the severity of hurricanes or tropical cyclones, because their strength is dictated largely by sea surface temperatures – so we could also use marine cloud brightening to cool the surface of the sea in the areas where these phenomena form. And it’s estimated that if you were to deploy marine cloud brightening worldwide, on a very large global scale, it could halt warming to 1.5 degrees for a number of decades, and up to a doubling of the current CO2 in our atmosphere.”
Clouds are made up of cloud droplets, and each droplet must form on something solid, called a cloud condensation nucleus. Over the ocean, clouds typically form around salt particles that are created by waves crashing and sea spray, and the size of these salt particles dictates the size of the cloud droplets. The reason why rain clouds are dark is because the droplets are very large, whereas white fluffy clouds are made up of very small droplets. Marine cloud brightening aims to deliberately inject very small salt crystals into already existing clouds to try to make the droplets smaller within those clouds, thus making the clouds brighter and whiter.
Jake is researching two different types of nozzles that can atomise seawater and fire tiny salt crystals into the sky to help the formation of whiter clouds.
He says: “Since I became aware of the climate situation, I have felt like I had moral obligation to do this work. We are making people aware that we may need something other than just emission cuts to tackle climate change. I think this is a relatively new idea for most people. Climate repair is not a substitute for emissions reduction or a long term solution to climate change. It must be used alongside deep and rapid emissions reduction.”