Lord Justice Lindblom said: “The Paris Agreement ought to have been taken into account by the Secretary of State. The National Planning Statement was not produced as the law requires.” He said the government had seen the ruling in advance but did not seek permission to appeal to the supreme court.
“The court ruling is bad news for all businesses and investors in the carbon economy, who will have to factor in the increasing risks of legal challenges,” said Tim Crosland, at legal charity Plan B, which brought the challenge. “But really it is good news for everyone, since all of us – including businesses and investors – depend on maintaining the conditions which keep the planet habitable.”
Plan B’s challenge was one of a number of legal challenges against the government’s national policy statement, which gave the go-ahead for the new runway in 2018 after MPs backed it by a large majority. Others were brought by local residents, councils, the mayor of London, and environmental groups including Friends of the Earth and Greenpeace.
The challenges were dismissed in the high court in May 2019 but the complainants took their cases to the court of appeal, which delivered its verdicts on Thursday.
Plan B argued that the Paris agreement target, which the government had ratified, was an essential part of government climate policy and that ministers had failed to assess how a third runway could be consistent the Paris target of keeping global temperature rise well below 2C, and close to 1.5C if possible.
In a witness statement, the then transport secretary, Chris Grayling, said the 2015 Paris agreement was “not relevant” to climate policy and assessing the plans against the earlier and less strict Climate Change Act of 2008 was sufficient. But the court of appeal disagreed.
“This is an opportunity for Boris Johnson to put Heathrow expansion to bed and focus on the most important diplomatic event of his premiership, the UN climate summit in Glasgow in November,” said Lord Randall, a former Conservative MP and climate adviser to the former prime minister Theresa May. “It’s his chance to shine on the world stage.” On 12 February, Johnson said in parliament: “I wait to see the outcome of the various legal processes that are currently under way.”
The court of appeal did not overturn the high court’s dismissal of the other challenges on Thursday, which related to air and noise pollution, traffic, and the multibillion pound cost of the runway.