With net zero policies under attack from elected far-right populists as well as autocratic petrostates, and another summer of record-breaking temperatures in Europe, the failure to decarbonise the world’s power supply is as gravely concerning as ever. But the UN secretary general, António Guterres, struck an optimistic note in a recent speech in New York. The world, he said, “is on the cusp of a new era … The sun is rising on a clean energy age.” Pointing to falls in the cost of onshore wind and solar, and the risk of further gas-price shocks in future, he called on big technology companies – whose datacentres are one reason for soaring energy use – to adopt a target of 100% low-carbon electricity by 2030.

Given US president Donald Trump’s personal hostility to renewable energy, Mr Guterres may be right that it makes more sense to demand action from US businesses at this point. In Scotland earlier this week, Mr Trump launched his latest misleading tirade, urging European leaders to “stop the windmills”.

His repeated attacks on wind power, as well as the recent cancellation of billions of dollars of green energy investment, make Mr Trump a destructive outlier. But populist parties in other countries are also ramping up their opposition to climate goals. In the UK, such positions were once confined to the political fringe. Now, the Conservative leader, Kemi Badenoch, is a net zero sceptic who has floated the possibility of a future government quitting the Paris agreement, while her acting shadow energy secretary, Andrew Bowie, accused the UN’s most senior climate scientists of bias.

This disturbing shift rightly provoked a strong response from the government. In July Ed Miliband called out Ms Badenoch’s party for its irresponsible and anti-science stance. With the UN’s deadline for countries to present their climate plans (known as nationally determined contributions) coming up, Mr Miliband deserves praise for his commitment. Climate diplomacy depends on politicians having the courage to face down opponents – and convince the public that a safe and secure energy future is within reach.

This is the prospect held up by Mr Guterres, who hopes it will galvanise much-needed action. The goal, agreed two years ago, of tripling global renewable energy capacity by 2030, is nowhere near being reached. With the UN climate summit nearing, all eyes are on China – the key player in the global renewables boom and the fight to stay within  climate limits.

Internationally, and domestically, renewables are the right choice. Colonial rule saw Carbon Brief rank the UK as the world’s fourth-largest historical emitter, behind only the US, China and Russia. To keep UK public support strong for green policies, energy ministers – notably Mr Miliband – must ensure a well-planned green transition to bring down prices. Grids need upgrades to handle wind turbine growth. Supply chain bottlenecks and concerns about human rights in critical minerals mining must be addressed.

In Britain, proposals from Labour MPs to reform energy billing – cutting costs for low-income households that use less power – aren’t just about lowering inflation. They raise a deeper question of fairness, and deserve serious attention as a step toward a more equal energy system, potentially through a social tariff. Ultimately, reforms should cut gas’s sway over electricity prices and couple optimism on renewables with honesty about the challenges.

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