Keir Starmer will face a key test of his claims to leadership on the climate early next year, when the UK’s statutory advisers issue their latest advice on future cuts to greenhouse gas emissions.The independent Climate Change Committee will set out recommendations on the UK’s seventh carbon budget on 26 February. At the core of the budget will be an overall cap on emissions for the years 2038 to 2042, needed to meet the legal obligation of reaching net zero emissions in 2050.While the scope of this budget will fall long outside the current parliament, policies to achieve the recommended cuts will be needed much sooner. By 2035, the UK should already have slashed emissions, relative to 1990 levels, by about 81%, according to the international pledge unveiled by Starmer at the Cop29 UN climate summit in November.The seventh carbon budget will need to go beyond that: by 2040, emissions should be about a quarter of what they are today.Ed Matthew, campaigns director at the E3G thinktank, said: “The seventh carbon budget should not be met with fear. It is the opportunity to put the finishing touches to a project to rewire the UK economy, to make it globally competitive and help nature to flourish. The only question is whether our leaders have the courage to be ambitious and stand up to the vested interests standing in our way.”That will require not just the decarbonisation of the power sector, which Labour has made one of its flagship “missions”, but also drastic changes in many other sectors of the economy. Fossil-fuelled cars must be switched for electric vehicles, and a widescale revival of public transport will be needed; homes must be insulated, and gas boilers exchanged for heat pumps; big changes will be needed to farming practices; new techniques for industry; and tree-planting and nature programmes will be needed to restore the UK’s carbon sinks.For Ed Miliband, secretary of state for energy security and net zero, setting a new carbon budget has a personal resonance. When Labour was last in power, he took on the role of the secretary of state at the newly created Department of Energy and Climate Change in October 2008. A month later parliament passed the Climate Change Act, under which the five-year carbon budgets are set.Requiring governments to set limits on emissions far in advance of their own term was intended to create long-term certainty, helping national and local government to plan, and giving businesses the signals and clear direction of travel they need to invest in the shift to a low-carbon economy.The CCC cannot require the government to legislate for particular policies, but gives guidance on where emissions cuts need to fall, and suggests an overall cap, which the government can only reject in exceptional circumstances.Starmer and Miliband have both already taken to the world stage to claim global climate leadership for the UK, so rejecting CCC advice would be a major departure. A Department for Energy Security an