Climate campaigners celebrated an "amazing and historic win" Thursday after a United Kingdom court ruled against plans to build a third runway at London's Heathrow Airport because the government's approval of the expansion "had not taken into account its own firm policy commitments on climate change under the Paris agreement."

The Court of Appeal, which is second only to the U.K.'s Supreme Court in England and Wales, called the government's failure to consider its climate obligations "legally fatal" and said that "the court will not permit unlawful action by a public body to stand." Heathrow is Europe's busiest airport and its two runways are currently at full capacity.

Although the court's ruling means the third runway could still technically be built in the future, advocacy groups opposed to the airport's expansion welcomed the Thursday's decision as a victory. As Friends of the Earth put it: "This ruling is an historic and groundbreaking result for climate justice and for future generations."

Brilliant news! This is a ruling on the side of climate and intergenerational justice There’s no hiding place for big emitters like #Heathrow Bottom line is no airport expansion in UK is compatible with the climate science #NoThirdRunway@The_AEF https://t.co/9T55LYgx8I — Caroline Lucas (@CarolineLucas) February 27, 2020

Putting the legal win into a global context, Friends of the Earth tweeted that the court's decision is "a victory for all those facing flooding in the U.K. right now, for those who've had to flee fires in Australia, for the people around the world on the front line of this #ClimateCrisis."

U.K. Transport Secretary Grant Shapps responded to the ruling on Twitter, saying that "airport expansion is core to boosting global connectivity. We also take seriously our commitment to the environment. This [government] won't appeal today's judgement given our manifesto makes clear any #Heathrow expansion will be industry led."

Heathrow Airport—which is owned by Ferrovial, Qatar Investment Authority, and China Investment Corp—said Thursday that "we will appeal to the Supreme Court on this one issue and are confident that we will be successful. In the meantime, we are ready to work with the government to fix the issue that the court has raised."

Tim Crosland, director of the British legal charity Plan B, which brought the legal challenge, welcomed the court's decision and the government's acceptance of it.

Incredible moment! The Court of Appeal has just ruled that the the Government policy to expand Heathrow is "unlawful" because it failed to take account of the Paris Agreement.https://t.co/L1XUY07cAS#BellTollingOnCarbonEconomy — Plan B Earth (@PlanB_earth) February 27, 2020

"It would have been hard to imagine this outcome even a couple of years ago, but as the scale and impacts of the ecological crisis become clearer, with people dying and being displaced in the U.K. and around the world, it's vital we reject the politics of division and unite in adversity," Crosland said in a statement (pdf).

"This is an important moment for all of us, and for our young people in particular. Some sanity is finally prevailing," he added. "It's all those people who have been working so hard to sound the alarm, whether by taking to the streets or in other ways, who have made this outcome possible. The message is finally getting through. The bell is tolling on the carbon economy loud and clear."

Plan B along with fellow climate campaigners and experts suggested that the ruling could have far-reaching consequences in terms of forcing governments worldwide to honor their climate commitments. Margaretha Wewerinke-Singh, an international public law expert at the Netherlands' Leiden University, told the the Guardian that "its implications are global."

"For the first time, a court has confirmed that the Paris agreement temperature goal has binding effect," said Wewerinke-Singh. "This goal was based on overwhelming evidence about the catastrophic risk of exceeding 1.5°C of warming. Yet some have argued that the goal is aspirational only, leaving governments free to ignore it in practice."

HUGE NEWS "The court’s ruling is the first in the world to be based on the Paris agreement [and may inspire] challenges against other high carbon projects."https://t.co/9fFBzUlnBf — 350.org Europe (@350Europe) February 27, 2020

Advocacy groups from across the globe took to Twitter Thursday to express excitement over the court's ruling:

Plans for a third runway at Heathrow have been ruled illegal by the Court of Appeal! This is especially good news as the court’s ruling is the first in the world to be based on the Paris agreement.#NoMoreAirportExpansionhttps://t.co/rCJYNsy29a — YouthStrike4Climate (@Strike4Youth) February 27, 2020 HURRAH! Landmark ruling finds Heathrow expansion illegal on climate grounds. Congrats to all who fought for this! Lots more fights across Europe.

No airport expansion is compatible with a #ClimateEmergency.#StayGrounded #Flygskam #NoThirdRunwayhttps://t.co/3AkPdEUXbM — Greenpeace EU (@GreenpeaceEU) February 27, 2020 This is HUGE! "Plans for a third runway at Heathrow airport have been ruled illegal by the court of appeal because ministers did not adequately take into account the government’s climate change commitments." This is how to act in a #ClimateEmergency a href="https://t.co/5M9utu1Cen">https://t.co/5M9utu1Cen — Extinction Rebellion (@ExtinctionR) February 27, 2020

Climate activists in the U.K. and beyond also celebrated the news on social media:

“Heathrow third runway ruled illegal over climate change.”

Imagine when we all start taking the Paris Agreement into account... https://t.co/7ostsjadKF — Greta Thunberg (@GretaThunberg) February 27, 2020 A big big win, as a court says no to expanding Heathrow airport on the (entirely obvious) grounds that it does not fit with the commitments the UK made in Paris accords. Huge implications for carbon-spewing projects in many places!https://t.co/7fFtiQC8xm — Bill McKibben (@billmckibben) February 27, 2020

British politicians at various levels of government also welcomed the court's decision:

Absoutely incredible news. It doesn't take a genius to work out that expansion is fundamentally incompatible with our climate targets and just transition. This is true politics and activism in action - expect much more of this going forwards. https://t.co/5pDUcptCNn — Clive Lewis MP (@labourlewis) February 27, 2020 WE HAVE WON After years of campaigning and legal challenges, today courts have ruled that a 3rd runway at heathrow is incompatible with our climate change commitments. No amount of big money or corporate lobbyist could win this fight https://t.co/u2ehLpLlUY — Ali Milani (@ARMilani_) February 27, 2020 BREAKING: We won! Today we blocked the Tory government plans to build a third runway at Heathrow Airport. Today’s judgment is a major victory for all Londoners who are passionate about tackling the climate emergency and cleaning up our air. https://t.co/59MEn2X6Lw — Sadiq Khan (@SadiqKhan) February 27, 2020

"Today's landmark judgement against a third runway at Heathrow is the most important environmental case for a generation, but we will not stop here," London Mayor Sadiq Khan vowed Thursday. "The fight for a greener, cleaner London continues."