Friends of the Earth has said it will appeal against the ruling by judges to dismiss five legal challenges to expansion at Heathrow airport, because the decision is “outdated in an ecological and climate emergency”.

The campaign group mounted one of five judicial reviews challenging the legality of the government’s verdict to allow a third runway at the airport.

But judges on Wednesday ruled against all the challenges, saying they understood the claimants held “strong and sincere views” but the hearing was only concerned with the legality of the government policy that had approved the expansion.

The high court ruled that the government’s national policy statement, which supports Heathrow expansion, was legal.

“We understand that these claims involve underlying issues upon which the parties – and indeed many members of the public – hold strong and sincere views,” said Lord Justice Hickinbottom, sitting with Mr Justice Holgate, in the ruling.

“There was a tendency for the substance of the parties’ positions to take more of a centre stage than perhaps it should have done, in a hearing that was only concerned with the legality, and not the merits, of the airport’s national policy statement.”

Friends of the Earth had taken the government to court on the expansion saying it was unlawful because it failed to take into account the requirements under the Paris agreement to take mitigating action to tackle climate change.

But the judges said the claimants faced an “overarching difficulty” which was that the agreement does not form part of UK law. They said the secretary of state did not arguably act unlawfully by not taking into account the details of climate change mitigation in the agreement.

They said: “Until parliament decides if and how to incorporate the Paris agreement target, it has no effect in domestic law.”

But Craig Bennett, Friends of the Earth’s chief executive, said he believed the court had got it wrong: “We are in an ecological and climate emergency and parliament have supported an outdated decision to chase climate-wrecking development. How can we take any government remotely seriously when they claim to care about climate chaos while supporting this runway?

“We are going to continue this fight because it’s about more than a runway, it is actually about a future fit for our children.”

One of the five legal actions was taken by a coalition of Greenpeace, the mayor of London, and councils including the prime minister’s local authority, Windsor and Maidenhead, which will be affected by noise and pollution from the increased number of flights.

The mayor, Sadiq Khan, is considering whether to appeal the judgment. Shirley Rodrigues, the deputy mayor for environment and energy, said: “In challenging the decision to expand Heathrow, [Khan] stood up for Londoners who have serious concerns about the damaging impact it will have on air quality, noise pollution, existing road and rail networks, and quality of life in our city.

“We will now consider the judgment and consult our co-claimants before deciding our next steps.”

John Sauven, the executive director of Greenpeace UK, said the main concern over the ruling was allowing Heathrow – the UK’s biggest carbon emitter – to expand in the middle of a climate emergency.

“For as long as climate change remains an afterthought in government decisions, they are kicking our children in the teeth. Our children’s future, not the aviation industry’s expansion, should be our nation’s number one priority. Until it is, our commitment to opposing this disastrous scheme through every avenue available will continue,” he said.

The transport secretary, Chris Grayling, said the expansion was vital and would be a massive economic boon to businesses and communities across Britain. He claimed it would be “at no cost to the taxpayer” and “within our environmental obligations”.

Grayling added: “I now call on all public bodies not to waste any more taxpayers’ money or seek to further delay this vital project, which will benefit every corner of the United Kingdom.”

Facebook Twitter Pinterest The shadow chancellor, John McDonnell, joins anti-third runway protesters outside the high court in London. Photograph: Mark Thomas/Rex/Shutterstock

Speaking after the ruling, the shadow chancellor, John McDonnell, said the decision let the government “off the hook”.

He added: “What I find extraordinary in the judgment is that, on the issues with regard to climate change, the government gets off the hook simply because it has not adopted the Paris agreement into UK law.”

Support from Labour MPs helped push through the proposals to expand Europe’s busiest airport, with an overwhelming majority of 296 in a House of Commons vote in June last year.

The decision came on the day MPs debated whether to declare a climate emergency in the UK, after weeks of high-profile direct action by Extinction Rebellion campaigners.