The head of climate change at the UN has warned that world leaders are still “far away” from securing a deal to limit the disastrous effects of global heating, with less than five months to go before a key summit in Glasgow. Time is now running out, said Patricia Espinosa, who was formerly foreign minister of Mexico but now leads the UN on climate policy. She told the Observer that although advances had been made at the G7 meeting in Cornwall last weekend, progress had not been made on honouring past commitments to find $100bn (£72.5bn) a year to help developing countries invest in green technologies. “We’re still very far away from being fully confident of having a full success at Cop26,” she said. The UN climate conference, opening on 31 October in Glasgow, is considered to be of special importance in the battle against global warming, which is now melting ice sheets, raising sea levels, destroying coral reefs and disrupting weather systems across the planet. The Paris climate agreement in 2015 pledged that nations would try to limit temperature rises to less than 1.5C by drastically limiting fossil fuel emissions, the principal cause of global heating. Glasgow will be the first opportunity to assess the impact of the promises made in Paris and to implement new measures to avert global catastrophe. The G7 had offered hope that this process could be boosted in advance of Cop26, but Espinosa expressed disappointment, saying: “Regarding finance, I’d have really hoped for a clearer signal on how and when we will be able to see the commitment to mobilise the $100bn fulfilled.” Honouring the pledge is seen as critical if developing countries are to come into line with plans to cut emissions and take costly steps necessary to reduce their reliance on fossil fuels. At the G7, there were commitments to get to the target before Cop26, but a lack of detail remained about precisely how much money wealthier nations would be willing to give. “This is one condition to be able to have a good basis to have a successful Cop26,” Espinosa said. “It is essential. We cannot afford a lack of success. Cop26 should be able to give some sense of hope to the world. “There isn’t much time. We are already in the second half of June.” This point was backed by Rachel Kyte, dean of the Fletcher School at Tufts University in Massachusetts, and a former UN climate envoy. “The G7 failed to lead when it didn’t agree how to fulfil the $100bn promise. Their apparent strategy of brinkmanship is wrong-headed. Many around the world are already at the brink,” she said. “The UK has six months left to its G7 presidency and five months to go until Cop26. Johnson has to muster the world to significant climate finance commitments, purposing development finance and detail behind the global Marshall plan that President Biden calls Build Back Better World. Then, and only then, can we get the agreement we need in Glasgow.” Espinosa added that there were still doubts about whether the summit would be held with all delegates attending in person, or whether it might be staged partly or wholly in a virtual format. If there were surges in Covid-19, plans would have to be adapted accordingly. “We are working on all possible scenarios, from a fully fledged conference to a conference that could be virtual,” she said. “It is true the UK presidency is working very hard to have a physical meeting.”