Is it time to start talking about geoengineering?

How the climate conversation is shifting in new ways

Photo by Laura Lezman on Unsplash

I’m just back from Climate Week in New York, where one topic kept surfacing in the corridors and behind the scenes: geoengineering. Some call it solar radiation modification (SRM). Whatever the name, it’s now firmly on the agenda.

That was striking, because on the main stage at the UN General Assembly the theatre felt almost irrelevant. Trump rambled to the UN for an hour like a crazy uncle in a bar, pausing only to trash-talk renewables and telling world leaders their countries were going to hell. Nobody cared. It was entertainment, not policy.

Then, embarrassingly for the West, Xi Jinping offered new national climate targets. They were weak, and likely to be overtaken by China’s own rapid clean-energy transition, but they underlined a stark reality: the US is becoming functionally irrelevant to climate and energy policy worldwide. China is now the big player in town.

What really struck me at the UN was that people are no longer talking about America’s position. They’re talking about how to deal with a rapidly warming planet — and whether tools like SRM might soon have to be part of the conversation.

The Earth isn’t waiting for us to cut emissions. At the UN, Barbados prime minister Mia Mottley — speaking for 74 climate-vulnerable countries — warned that we’ve already “hurtled past 1.5 degrees”. For those who fought to enshrine 1.5°C in Paris, that’s a crushing blow.

The World Meteorological Organisation says we could officially cross 1.5°C as soon as 2028. And it’s not just CO₂ driving the heat. The second-largest driver of rising temperatures is now the removal of sulphate aerosols from the lower atmosphere due to pollution controls on shipping fuels and coal-fired power, according to climate scientist Zeke Hausfather.

That’s why Hausfather and Harvard’s David Keith used Climate Week to argue in the New York Times for more research in order to help us consider whether we need a small program to boost stratospheric reflectivity by putting aerosols there artificially — offsetting the lost cooling as sulphur in the lower atmosphere disappears due to pollution controls.

They’re not alone. In a closed UN session I attended, climate vulnerable countries agreed that research is essential to inform decisions. Even veteran US climate campaigner Bill McKibben isn’t ruling it out. On my podcast, he admitted: “we may reach a point in the not very distant future where we end up just breaking the glass and pulling that handle”.

Hausfather estimates that sulphate aerosols are currently masking about half a degree of warming. If we reach net zero and stop burning fossil fuels, that cooling vanishes — adding that missing half a degree and pushing us past the Paris fallback of 2°C. The impacts hardly bear thinking about.

So why not move those cooling aerosols from the lower atmosphere — where they kill millions — into the stratosphere, where no one breathes them? In theory, this could hold temperatures down while avoiding health harms. More science, including modelling and trials, is needed to show what such a world might look like.

But there are strong objections too. Some argue that even researching geoengineering risks normalising it, creating a slippery slope toward deployment. And there’s the spectre of ‘termination shock’. Not to mention the governance issues: could we really take a legitimate collective decision as a species to directly fix our planet’s thermostat?

There has already been a major campaign to shut down SRM research entirely. Conspiracist MAGA politician Marjorie Taylor Greene has pushed bans in US states. And many environmental campaigners and scientists signed a “non-use” declaration explicitly opposing research, warning that SRM could distract from emissions cuts or unleash unknown risks.

I was invited to sign that letter, but I refused. I don’t ever want to close down science. Still, the question remains: is a geoengineered world really worse than a 2°C hotter one? Honestly, I don’t yet know what to think, but that’s the real question.

So that’s where I end up for now. It’s a tough choice — and the harsh truth is that perhaps the only physically plausible way to keep the 1.5°C goal alive is by cooling the planet artificially with sulphates. For now, I wouldn’t push that button. But I do want to see more research — including field trials — so we can better understand the consequences.

Should we do SRM? The answer may still be no. But an informed no is better than an ignorant one.