The government has been accused of "not taking the climate crisis seriously" after plans to drastically slash flight tax led to a spike in domestic flights.
Analysis by The Mirror and the Aviation Environment Federation (AEF) showed that extra routes introduced by one airline alone - which were directly linked to the cut - will dump more than 9,000 tonnes of CO2 into the atmosphere each year.
Airlines including Ryanair and easyJet pushed hard for the cut - which will see Air Passenger Duty (APD) down 50% to £6.50 from April 1. (This is due to rise again next year to £7 following the government's Spring 2023 budget announcement).
Ryanair said the tax break would help the company sell more budget domestic flights, while also arguing against a frequent flyer tax on the ground it would "punish" passengers.
During consultation into the proposals, rail industry insiders warned that the change could lead to 27,000 tonnes of emissions more being released and 220,000 fewer rail journeys in the UK a year as people swap expensive trains for cheaper planes.
Since summer 2022 Ryanair has added four new domestic routes, meaning around 2,200 extra flights across the UK each year, which will dump 9,300 tonnes of CO2 into the atmosphere, according to AEF and Mirror analysis.
Airlines UK, a trade body representing all the major UK airlines, applauded the tax cut and said it "strongly supported" it.
It cited a study that claimed abolishing APD completely would lead to 66 new routes being added, including 20 domestic, and argued a 50% cut would have a similar impact.
EasyJet predicted the 50% cut would allow it to continue flying newly established routes including Belfast to Inverness and Edinburgh to Bournemouth.
It also said the cut could lead to a 36% rise in the number of flights between Liverpool and Belfast, and by 35% between Bristol and Edinburgh.
The shift to domestic aviation has been seen as a big backwards step in the battle to cut emissions amid the worsening climate crisis.
Per passenger, domestic flights are between four and six times more polluting per kilometre than domestic trains.
An environmental impact assessment only released by the Treasury following a Freedom of Information request shows a predicted rise in 15,000 tonnes of emissions from domestic aviation in 2023 following the tax cut.
EasyJet told the Treasury that its "domestic volume" would rise by 31% due to the cut, while BA’s owner International Airlines Group suggested "new routes, increased frequency and larger aircraft" would follow, submissions obtained by OpenDemocracy show.
By offering tax breaks to airlines, the UK is heading in a different direction to countries including France, which has banned most domestic aviation routes where there is an equivalent rail journey.
In Germany and Spain the governments have poured money into making greener rail journeys cheap or free, in a bid to get people out of the air and onto the rails.
In comparison, UK rail tickets increased by 5.9% on March 5 - the largest fare rise in a decade.
"The hoped-for increase in domestic flight numbers as a result of this decision indicates that the Government is not taking the climate crisis seriously," Max Thrower of AEF said.
"While they have tried to balance the domestic APD cut with an increase for passengers flying ultra-long routes, the focus should have been on reducing emissions overall.
"Whatever the behind-the-scenes politics of this change might be, it gives the impression that yet again, the wishes of the industry have been put first, rather than the communities affected by increases in noise and pollution.
"For an industry which pays no fuel duty or VAT on tickets, the Government should be looking at tax increases to ensure that airlines make a fair contribution to public finances.
"Given the scale of the challenge to deliver net zero aviation by 2050, any measure designed to boost passenger demand should be off the table."
The Treasury has said the predicted increase in domestic aviation emissions would be partially offset by a reduction in long-haul emissions due to a 3.5% duty increase from April. By 2025 the government body says the rise will be completely offset.
A spokesperson for the Treasury said: “We are absolutely committed to delivering on our net-zero commitments.
“That’s why private jets will be excluded from the domestic Air Passenger duty cut and a new ultra-long haul is being introduced to ensure that those who fly furthest contribute the most.
“As set out in the FOI response, the total impact on emissions of both reforms is estimated to be zero.”
Although airlines pushed for the cut in APD, they also argued that it should be scrapped completely.
EasyJet has argued domestic APD should be cut as they claimed "shorter flights are the least carbon emitting", but also called for it to be abolished, which add 4.4million more domestic easyJet passengers a year, urging the government to introduce a carbon tax instead.
Both easyJet and Ryanair argue the tax is targeted poorly, as it does not offer relief for more efficient, fuller aircraft.
The Business Travel Association backed the cut, saying it would "support the levelling up of the UK and speedier post-pandemic recovery".
On the other hand, some of the strongest criticism came from the Rail Delivery Group, which warned: "If not managed carefully, such a policy would have a profound environmental impact, incentivising mode shift away from rail and resulting in significantly higher carbon emissions in the UK."
They added: "The UK Climate Change Committee considers the achievement of net-zero carbon aviation by 2050 ‘highly unlikely’.
"Hence the government should continue to invest in conventional and high-speed rail infrastructure to improve connectivity, performance and support rail decarbonisation."
First Group - which operates a fifth of local bus companies in the UK and five train operating companies - also argued against the cut, saying it would push people away from trains.
"A recent study by the climate charity Possible found that cost is a vital factor in passengers’ travel habits," the company noted.
"40% of survey respondents stated that it would be essential for a train journey to be cheaper than a plane ticket to consider choosing rail over air travel."
