Climate Repair and Timescales for Action

Cooling the planet with aerosols in the stratosphere would mean putting 10 million tonnes a year up there. Today, Hugh Hunt said, researchers are not allowed to release even one kilogram. Hugh, of the Centre for Climate Repair at Cambridge University, believes the world will need such cooling long before emissions cuts deliver. The session hosted by Hugh and Lukas Gast of University College London kept running into the same obstacles, and they had less to do with engineering than with permission and reputation.

Two centuries off fossil fuels

Hugh drew the napkin diagram, global temperature rising against time, which is also printed on the back of Hugh's business card. Cutting emissions comes first, but Hugh expects getting off fossil fuels to take a couple of centuries. Removing carbon, with the world still emitting 40 billion tonnes of CO2 a year, will take one or two centuries too. "Net zero by 2050 is a pipe dream. It's not going to happen," Hugh said.

That leaves a gap for solar radiation modification: brighter clouds, a change to the chemistry of the stratosphere, perhaps reflectors in space. Mount Pinatubo cooled the planet by about one degree over a year in 1991, and stratospheric aerosols would copy the volcano. Most climate scientists still hold that getting off fossil fuels is the only step that matters, a view Hugh said fitted 20 or 30 years ago and no longer does.

Lukas supplied the industrial arithmetic. The world makes about 2,000 million tonnes of steel a year from almost no fully net-zero sites, and less than 0.1 million of its 100 million tonnes of hydrogen is made with electricity. A steel plant that will need CO2 or hydrogen pipelines in ten years' time faces 5 to 15 years of permits and construction.

Hands and legs tied

Regulation was the greatest challenge, said an investor in a stratospheric aerosol company. Hugh drew a line between deployment, which is decades away, and research, which releases nothing into the atmosphere and is still the target of calls for regulation. Researchers are left trying to win over investors with their hands and legs tied.

A carbon-removal specialist wanted more attention on sunlight reflection because the AMOC, the part of the Gulf Stream that warms northern Europe, could tip. They pointed to the NGO Reflective's ten-year research agenda, which aims at readiness to lower temperatures fast if tipping points come close, not at deployment now. Hugh proposed a narrower target. Arctic ice controls the AMOC, so refreezing the Arctic might do more than cooling the whole planet, perhaps using old oil platforms for cloud brightening. But Cambridge, Hugh said, may not take money from the fossil fuel industry.

Net zero by 2050 is a pipe dream. It's not going to happen.

Old sites with permits in place

The rest of climate action is slow for more ordinary reasons. A green-cement founder recalled a carbon capture and storage project in Norway that took ten years from the first engineering study to capturing any CO2, at a cost that could not compete. The founder wanted policy that helps the big cement and steel makers retire production lines 40 to 50 years old, instead of giving them incentives to keep those lines running.

Speed is possible under pressure. Lukas pointed to Germany, notorious for slow permitting, building LNG terminals within a year. The most practical ideas were about sites that already hold permits. An investor described a German utility that must by law shut down a former nuclear site. Decommissioning might cost a billion, while a few million spent rebuilding it for start-ups costs far less, so the site is becoming a fusion research site with start-ups and their supply chain on it. Another participant pointed to chemical parks that are losing companies, where the fire service, water and power are already in place. Cement and steel sites, Lukas added, usually come with ports and permits for hazardous operations.

Pariahs and cowboys

Reputation proved harder to fix than permits. Hugh said companies such as Stardust, which is working on stratospheric aerosols, are treated as pariahs, even as evil, and investors do not want to back an evil business. An angel investor recalled a climate-repair CEO who avoided interviews for fear the public would treat repair as a reason to stop cutting emissions. They had also assumed that watching France burn would move opinion as Russia's invasion moved money into defence. It had not. People buy air conditioning, Hugh said. Greta Thunberg is right that when you are in a hole you should stop digging, but the hole is filling with water, so a ladder and a pump are needed too.

Remedies were thin. One participant wanted more public figures to back the research and SRM sold to governments as a service, not as credits. Hugh warned how quickly it could become a cowboy industry. Make Sunsets launches sulphur dioxide balloons in California and is paid $500 per balloon for a credit, with zero evidence of any effect.

The last question was whether insurers, who pay for much of the flooding, might become allies. They ought to be interested, Hugh said. Marine cloud brightening could cool the Atlantic ahead of approaching hurricanes. But the idea draws conspiracy theories that someone will steer a storm onto Florida instead of South Carolina, and once those start, no insurer will touch it. Even where climate repair has a natural customer, the customer is afraid to be seen with it.

This Ripple was hosted by Hugh Hunt (Centre for Climate Repair, Cambridge University) and Lukas Gast (University College London) at The Drop 2026 on 16 September.