Court agrees with campaigners that the 2016 Paris Agreement must be honored

In a huge victory for environmental campaigners, the United Kingdom's Court of Appeal has ruled that plans for a third runway at London's Heathrow Airport are unlawful because they do not take into account the British government's climate commitments.

The ruling is believed to be the first in the world to factor in a country's obligations to the Paris Agreement on climate change, and could have far-reaching consequences for other contentious carbon-heavy infrastructure projects in the UK and elsewhere.

The ruling concludes a case brought last year against the secretary of state for transport by a cohort of individuals and organizations that opposes the government's Heathrow expansion plans, including London Mayor Sadiq Khan, campaign groups Friends of the Earth, Greenpeace, and Plan B, and several local authorities.

The court ruled that the government's plans, put forth in a document known as the Airports National Policy Statement, or ANPS, did not comply with the Planning Act of 2008, which legislates that such development plans must detail measures taken toward the mitigation of, and adaptation to, climate change.

The proposed third runway, which got the green light from Parliament in 2018, would mean more than 700 extra daily flights to and from Heathrow.

The court said the government had not adequately explained how it would off set the increased aviation emissions that the runway would cause while maintaining its commitments to the 2016 Paris Agreement on climate change.

"The Paris Agreement ought to have been taken into account by the secretary of state in the preparation of the ANPS and an explanation given as to how it was taken into account, but it was not," the judges said in their ruling. "That, in our view, is legally fatal to the ANPS in its present form."

The government said it will not appeal Thursday's ruling, and did not indicate whether it plans to present an updated ANPS.

Grant Shapps, the UK's secretary of state for transport, said: "Airport expansion is core to boosting global connectivity. We also take seriously our commitment to the environment. This government won't appeal today's judgment, given our manifesto makes clear any Heathrow expansion will be industry led."

Heathrow Airport confirmed it plans to challenge the decision, saying in a statement: "We will appeal to the Supreme Court on this one issue and are confident that we will be successful."

Khan called the judgment a "huge victory for everyone who is passionate about tackling the climate emergency", while Friends of the Earth said it was an "excellent example of how we can and should hold the government to account".

But Adam Marshall, director general of the British Chambers of Commerce, said many businesses in the UK will be "bitterly disappointed" by the ruling. He said the 14-billion-pound ($18 billion) expansion would have provided a major economic boost for the UK.

"Without expansion, firms risk losing crucial regional connectivity and access to key markets across the world," Marshall said. "Hundreds of UK companies are already invested in the supply chain for expansion, and tens of thousands of additional jobs will be created if the project goes ahead."

Margaretha Wewerinke-Singh, an expert in international climate change law at Leiden University in the Netherlands, said the "implications of this judgment are global".

"For the first time, a court has confirmed that the Paris Agreement temperature goal of pursuing efforts to keep warming below 1.5 C has a binding effect," Wewerinke-Singh said. "Some have argued that the goal is aspirational only, leaving governments free to ignore it in practice. The UK Court of Appeal's judgment demonstrates that this goal must be taken into account in climate policy, including when governments review and permit large infrastructure projects."