After an epic, years-long saga, the final decision on Heathrow Airport’s controversial third runway has been made. 

MPs gathered Monday to cast a final vote, on what transport secretary Chris Grayling has described as the “biggest transport decision in a generation.” 

As was widely expected, plans for the construction of a third runway at the London airport was approved, after the government issued a three-line whip to its MPs — meaning they were ordered to vote in favour. 

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But environmental campaign groups and activists have lined up to warn about the impact the expansion will have on Britain’s legally binding climate targets. 

Friends of the Earth’s Scotland branch said the expansion plan “flies in the face of efforts to tackle climate change.” 

“Aviation is the most polluting form of transport and the industry’s environmental impact is growing rapidly,” the organisation added. “Being a climate leader means saying no to polluting projects like this.” 

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Meanwhile, the World Wildlife Fund’s (WWF) climate specialist James Beard said: “We can live up to our commitments to tackle climate change or we can build a third runway. It’s almost impossible to do both.” 

WWF’s head of transport policy, Peter Lockley, previously warned: “Expansion at Heathrow would be a huge mistake as it suggests that, as a nation, we’re not really serious about tackling climate change.” 

“It would lock the UK into a high-carbon infrastructure at a time when scientists are telling us to quickly reduce our emissions if we’re to avoid dangerous climate change," he added.

WWF also said last year the new runway would make Heathrow the UK’s largest single source of greenhouse gases and increase emissions 15% over the limit advised by the Committee on Climate Change (CCC). 

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The vote comes three days before an independent committee will release a report that’s expected to warn that the third runway would lead to soaring emissions, and end Britain’s hopes to meet its targets for greenhouse gas reduction. 

The CCC’s report is also expected to say that for Britain to meet its targets would also require individuals to stop using their gas cookers, central heating boilers, and petrol cars. 

The committee’s chairman, Lord Deben, has already written to Grayling to warn about the Heathrow expansion’s effect on the environment, according to the Sunday Times. 

Critics have said the timing of the vote meant that MPs didn't have the chance to read the report before they made a decision.

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According to a 2016 report by the Airports Commission, aviation represents 6% of the UK’s total CO2 emissions and, it added, a third runway would increase that by a little less than 10%. By 2040, it predicted, aviation would represent 24% of all UK CO2 emissions. 

Yet to be in with a chance of hitting its greenhouse gas reduction targets, the CCC’s report is expected to say, British aviation mustn’t exceed its 2005 peak of 37.5 million tonnes of CO2. 

The Department of Tranport said in a report published on its website last week that, if the third runway goes ahead, aviation emissions would reach 43 million tonnes of CO2 by 2030, according to the Independent.

Ministers have reportedly said that the third runway project would have built-in environmental protections, and Grayling said aircrafts now are “breaking new frontiers” in becoming more environmentally-friendly, including through cutting fuel use, emissions, and noise. 

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“The Airports Commission came to a very clear view that we could expand Heathrow airport and still meet our climate change obligations,” said Grayling. 

“They gave it the thumbs up, they did lots of detailed analysis on this and they said ‘yes we can do this’,” he continued. 

He was also questioned about the environmental impact of the runway on BBC Radio 4’s “Today” programme, and added: “I think technology, over the next 20 or 30 years, is going to make a big difference in aviation.” 

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“It’s happening already, if you look at the new aircraft,” he said. “That’s going to make a huge difference to fuel consumption and emissions and noise at airports.” 

The expansion will increase Heathrow’s capacity from 85.5 million passengers to 130 million, according to the BBC. Meanwhile the government has also said the expansion won’t cost the taxpayer a penny, would create 100,000 jobs, and would benefit the whole country. 

Global Citizen campaigns to achieve the UN’s Global Goals, which include action on climate change, responsible consumption and production, and creating cities and communities that are sustainable. You can join us by taking action on these issues here. 

Update Tuesday, 26 June, 1:53 a.m. BST: This post has been updated to reflect the official Parliament vote.