Boris Johnson’s apparent willingness to sign off a new oilfield, Cambo, in the North Sea makes a mockery of his claim to global climate leadership. The first phase of Cambo would produce up to 170m barrels of crude. That is the equivalent, say Friends of the Earth, of the annual emissions of 18 coal-fired power plants. This sends dark clouds scuttling over the UK’s presidency of Cop26, held in Glasgow in November this year. For the UN climate summit to be a success, Mr Johnson’s team, headed by Alok Sharma, must cajole recalcitrant countries into line. It is doubtful that Mr Sharma can persuade other nations of the merit of forsaking fossil fuels when Britain will not lead by example.

Last week, the UN Intergovernmental Panel on Climate Change delivered its starkest warning yet about the planetary emergency. To have a 50% chance of keeping global heating below 1.5C requires the world to get net emissions of carbon dioxide down to zero before 2050. In a foreword to the IPCC report, Antonio Guterres, the UN secretary general, wrote that countries should “end all new fossil fuel exploration and production”. The International Energy Agency, an intergovernmental group founded to protect access to hydrocarbons, has said much the same.

Cambo, controlled by private equity giant Blackstone via Siccar Point Energy, is the first of three large UK North Sea ventures. An even bigger deepwater oilfield, Rosebank, is waiting to be exploited by Norway’s state-owned energy company. In 2023, BP hopes to start drilling in its Clair South reservoir. The industry says the UK needs domestic supplies, yet most of the oil will be exported. Mr Johnson’s defence is as thin as the paper it is written on. His government has promised it will put an end to new oil exploration licences. But fields like Cambo, argue ministers, are just extensions of old licences. Mr Johnson’s green agenda risks slipping beneath an oil slick.

Deciding what action to take is difficult and the trade-offs tricky. Nicola Sturgeon, the SNP first minister, has been accused, with some merit, of hiding behind Mr Johnson over Cambo. The oil sector plays an outsized role in the Scottish economy. The loss of North Sea jobs could be answered with a more interventionist industrial strategy.

Governments do not want to impose costs today when the benefits arrive after they have left office. This misses the existential nature of the emergency. Lord Deben, who chairs the government’s climate change committee, warned in March that Mr Johnson’s North Sea plans fell short of net zero targets. The prime minister did nothing. A summer of record temperatures and apocalyptic fires and floods vindicates in a very tangible way what scientists for years have been saying. Inaction by Mr Johnson risks doing more harm than any good he may achieve in Glasgow.