Removing CO2 from atmosphere vital to avoid catastrophic tipping points, leading scientist says

10bn tonnes must be captured from the air every year to limit global heating to 1.7C, says Johan Rockström

Field said 200bn tonnes of carbon dioxide would have to be removed from the atmosphere to cope with every tenth of a degree rise.

At the most, he said this could cope with two-tenths of a degree, but even this would be slow, expensive and could bring a wide range of unintended consequences.

There are a number of options for capturing carbon. The most effective and cheapest is growing forest, which costs about $50 (£38) for every tonne of CO₂, but means the land cannot be used for other purposes such as agriculture. The most expensive is direct air capture, an industrial process that has never been used at scale, which costs at least $200 per tonne. In between are riskier strategies such as ocean fertilisation, which could disrupt marine ecosystems.

Krug said the UN’s main climate science body, the Intergovernmental Panel on Climate Change (IPCC), had started a study on different mechanisms for carbon removal. Rockström told the Guardian he would like the Cop30 presidency to put carbon removal in its declarations to focus attention on the risks and costs ahead.

He said Potsdam Institute modelling had shown that, even with ambitious carbon removal and strong government actions to reduce emissions, it was still only possible to limit heating to between 1.6C and 1.8C. Even this would require far stronger policies to reduce fossil fuel emissions than those currently adopted by governments, which would allow the world to heat by at least 2.7C.

Despite the enormous costs involved, he said the alternative was more devastating droughts, fire storms and suffering.

“Every tenth of a degree matters,” he said. “We are seriously seeing that we are heading at high speed towards a dead end. Scientists continue publishing papers but we are getting nervous. We are seeing really worrying signs,” he said.

Scientists want the prevention of tipping points to be included in the global stocktake of the Cop process. Lenton said he welcomed the fact that the the IPCC had started studying these risks. He emphasised there were also positive tipping points, when social, economic or technological drivers could push change towards a more stable climate.

He said the Cop30 presidency’s willingness to engage was a good sign, though the political circumstances elsewhere in the world were making action difficult.

“I’d love to think this Cop could be its own tipping point,” he said. “It should be, in the sense that the tipping point risks are staring us in the face now, particularly, for example, with the coral reef collapse and the Amazon around us suffering extraordinary droughts and fires.

“There won’t be a new legally binding agreement, but the Cop presidency might put together some new alliances that take into account the tipping point risks and the potential for positive tipping point change. I think that could be the best outcome to hope for.”

One country that will not be part of any new alliance is the US, which under President Donald Trump has withdrawn from the Paris agreement again, and is one of four countries – along with Afghanistan, Myanmar and San Marino – not to register a single delegate at the summit.

Christiana Figueres, one of the architects of the Paris deal, expressed relief at the absence of the US, addressing Trump with the words “Ciao bambino!”

“I think it actually is a good thing,” she told reporters. “They won’t be able to do their direct bullying.

“Honestly, the decarbonisation of the global economy is irreversible,” she said. “Momentum is building into the point where it is simply unstoppable, with or without the US.”

Meanwhile, Ethiopia was named as the expected host of Cop32 in 2027, but the host of Cop31 next year remains uncertain, with neither of the two bidders, Australia and Turkey, showing any sign of backing down.

Cover photo:  Johan Rockström was among several leading climate experts at Cop30 who warned the world would overshoot the 1.5C target of the Paris agreement. Photograph: Christopher Hunt/The Observer