ClientEarth and Friends of the Earth say strategy fails to include policies needed to ensure emissions cuts.
The UK government is being sued over its net zero climate strategy, which lawyers argue illegally fails to include the policies needed to deliver the promised cuts in emissions.
Court papers were filed on Wednesday by ClientEarth (CE) and, separately, by Friends of the Earth (FoE). CE also claims the failure to meet legal carbon budgets would contravene the Human Rights Act by impacting on young people's right to life and family life.
The net zero strategy was published in October and included commitments to end the sales of new fossil fuel cars by 2030 and gas boilers by 2035. But it did not spell out how the strategy would be delivered or specify the cuts in emissions to be achieved in each sector. Instead, the lawyers said, it relied on speculative technologies such as zero-carbon aviation fuels and extracting carbon dioxide directly from the air and burying it.
ClientEarth has defeated the government three times in court in recent years over inadequate air pollution policies, while court victories by Friends of the Earth include a case about the cost of bringing environmental claims against ministers.
Both CE and FoE argue that the Climate Change Act requires ministers to set out policies to meet carbon budgets "as soon as reasonably practicable" after they have been set. The assessment included in the net zero strategy shows UK emissions being double the level allowed in 2035 and also missing targets in 2025 and 2030.
"A net zero strategy needs to include real-world policies that ensure it succeeds," said lawyer Sam Hunter Jones at CE. "Anything less is a breach of the government's legal duties and amounts to greenwashing and climate delay. The government's pie-in-the-sky approach pushes the risk onto young people and future generations who stand to be hit hardest by the climate crisis."
The FoE action also claims that another government strategy, on heat and buildings, failed to assess its impact on groups protected in law, including children, people of colour and those with disabilities. FoE previously found that people of colour were twice as likely to be living in fuel poverty as white people.
"We know that those who do least to cause climate breakdown are too often the hardest hit," said Katie de Kauwe, an FoE lawyer. "Climate action must be based on reversing these inequalities, by designing the transition with the most vulnerable in mind. Not even considering the implications of the heat and building strategy on such groups is quite shocking."
The government's official advisers, the Climate Change Committee (CCC), said in October that the net zero strategy was a "big step forward" and the most comprehensive among G20 countries. But its assessment said: "The government has not quantified the effect of each policy and proposal on emissions. So ... it is not clear how the mix of policies will deliver on its ambitions."
The CCC highlighted a lack of policies on energy efficiency in homes following a botched green homes grant scheme, on farming, and on reducing the amount of meat and dairy people eat and the number of flights taken. "It's a very market-led strategy," said the CCC chief executive, Chris Stark. "We shall see how that fares."
"While the government should of course invest and encourage innovation, the early-stage solutions featured in the strategy can't make up for the lack of credible near-term action," said Hunter Jones.
He added: "Energy bills are currently soaring, in part because of the UK's over-reliance on fossil gas for heating and poor levels of insulation. Government failure to deliver real climate action is resulting in higher bills for people."
Following the filing of the claims, and the submission of the government's defence, the high court will decide whether to grant full hearings of the cases.
A government spokesperson said: "The net zero strategy sets out specific, detailed measures we will take to transition to a low carbon economy, including helping businesses and consumers to move to clean and more secure, home-grown power, supporting hundreds of thousands of well-paid jobs and leveraging up to £90bn of private investment by 2030."