The prospect of limiting global heating to 1.8 degrees on the back of new commitments made at Cop26 is only "a hypothesis", according to Laurent Fabius, the former French prime minister who was president of the landmark 2015 Paris climate summit.
He said he was "very impressed" by commitments made in the first week at the Glasgow summit, including a deal to reduce the potent greenhouse gas methane, a net-zero target from India, and plans from China to reduce emissions and commitments on coal.
If those plans are fulfilled, according to International Energy Agency analysis, global temperature increases could be limited to 1.8 degrees, which is below the Paris agreement's upper goal of limiting rises to two degrees but well below its tougher aspiration of capping heating at 1.5 degrees above pre-industrial levels.
But Mr Fabius told the Guardian in an interview: “This is theoretical . . . It means if all that has been announced is delivered in full, which obviously is a hypothesis.”
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Announcements on coal, methane and deforestation had buoyed spirits inside negotiating rooms, he believed.
Mr Fabius, who chaired Cop21 in Paris, spent Thursday and Friday meeting with key lead negotiators as well as Cop26 president Alok Sharma, United States climate envoy John Kerry, Prince Charles, Scottish first minister Nicola Sturgeon, China's climate negotiator Xie Zhenhua and Indian prime minister Narendra Modi.
Speaking at a press briefing, he said negotiations “are more optimistic, less pessimistic than a few days ago”.
“It doesn’t mean that problems are solved, and I know by heart that you can only judge a Cop at the end of it. And sometimes there are surprises,” Mr Fabius added.