Fifa's claim that the Qatar World Cup will be carbon neutral is "dangerous and misleading" and the tournament could have a carbon footprint three times higher than stated, environmentalists say.
Football's world governing body is also facing challenges across Europe, and an open letter asking for its sustainability policies to be scrapped.
Fifa says the Qatar World Cup will have a footprint of 3.6 million tonnes of equivalent carbon waste, which will be offset by a number of initiatives.
"We did a little digging into Fifa's carbon footprint estimate and we think it's way over 10 million tonnes - so three times that, at least," said Mike Berners-Lee of Lancaster University.
And climate scientist professor Kevin Anderson of Manchester University said Fifa's claim is "deeply misleading and incredibly dangerous".
Anderson said: "There will be a direct human cost to this tournament. This is a huge amount of emissions for one sporting event. It's these emissions that will have an impact around the world."
Berners-Lee also said: "'Carbon neutral' is a dodgy term. The offset scheme the World Cup has chosen doesn't remove carbon from the atmosphere, so it's a bogus term. It's very misleading to call this a carbon neutral World Cup. They're not even removing carbon to compensate."
The open letter argues that Fifa's sustainability strategy has flawed carbon calculations, questionable offsetting practices and shifts the responsibility on to fans rather than shouldering it itself.
Fifa says that - of the 3.6 million tonnes of equivalent carbon produced for the Qatar World Cup, 51.7% of it is caused by travel, including fans' flights - for which it has pledged to offset every ticketholder's flight emissions, along with several other initiatives such as electric mobility for public transport around the tournament.
A Fifa statement read: "Fifa is fully aware that climate change is one of the most pressing challenges of our time and believes it requires each of us to take immediate and sustainable climate action.
"For the very first time, Fifa and the host country Qatar have pledged to deliver a fully carbon neutral World Cup. A comprehensive set of initiatives have been implemented to mitigate the tournament-related emissions, including energy-efficient stadiums and green-building certification of their design, construction and operations, low-emission transportation, and sustainable waste management practices.
"All remaining emissions will be offset through investing in internationally recognised and certified carbon credits. This is done on a voluntary basis, leading the way in the sports industry. More can be done and will be done, as Fifa has pledged through the UNFCCC Sports for Climate Action Framework and its own Climate Strategy to reach net-zero emissions by 2040."
'Infrastructure only built for this event,' says open letter
Norwegian international Morten Thorsby of German Bundesliga Union Berlin - whose country did not qualify for Qatar 2022 - represents players and bodies who are questioning Fifa's claim.
"This tournament is an absolute disaster in terms of its environmental footprint," Thorsby said in an open letter.
"They've been building infrastructure only for this event, which is never a good thing."
The letter asks Fifa to scrap its claims of carbon neutrality and review its approach to environmentally 'clean' tournaments in time for the 2023 Women's World Cup in Australia and New Zealand next July.
Signatories of the letter include Thorsby - who recently won a BBC Green Sport Award for his climate awareness campaigning - Wycombe Wanderers' David Wheeler, Forest Green Rovers, Swedish player Elin Landstrom from Roma and Zoe Morse from Chicago Red Stars in the US.
The letter reads: "Climate change is the opponent we must tackle - and we're already deep into extra time. Whatever shirt we wear or chant we sing, we've got everything to gain from taking action. But, instead of taking this golden chance, Fifa's currently set itself up to miss its best shot at goal.
"The tournament has been labelled as the first 'fully carbon neutral Fifa World Cup tournament', meaning its overall impact on the planet should be zero."
Who are making the challenges?
Advertising complaints have been lodged in the UK, France, Switzerland, Belgium and the Netherlands against Fifa's promotion of the Qatar World Cup's carbon neutrality claims.
The challenges centre on the argument that Fifa's claim of a carbon neutral World Cup is false because of an underestimation of emissions and a lack of credibility in its offsets, which, say campaigners, means consumers and fans are being misled.
The New Weather Institute has made the challenge in the UK. In Switzerland Klima-Allianz Schweiz [Climate Alliance] has made a similar complaint, alongside France's Notre Affaire a Tous, Belgium's Carbon Market Watch and the Netherlands' Fossil Free Football.
What do we know about Fifa's sustainability challenges?
The carbon neutrality claim of the Qatar World Cup was called into question earlier in the year, with Carbon Market Watch saying in a report it involved "creative accounting" and was "misleading".
The letter also notes that travel estimates are "wildly underestimated" and that claiming a tournament is carbon neutral before it has happened is "impossible to predict".
It also doubts the efficacy of carbon reduction projects and how they are measured.
Anderson added: "These big events, whether the World Cup or any other sporting or music event, to claim events are carbon neutral is deeply misleading and is making the situation worse rather then better."
"We are trying to hold the sea temperature rise to 1.5C - already we are very near to that. There's very little emission space left to assume we can fly people around the world and, somewhere else in the world, expect people to make changes in their behaviour to compensate means we are not learning how to do things differently."
Anderson said the idea that "there's always an easy way to solve it with a few pounds for an offset" is "incredibly dangerous" and "demonstrating really bad behaviour".
"Fifa... just did the usual thing: let's go to a fantastic venue and let's just have a few offset credits to cover it. No innovation, no real thinking, no leadership; at every level Fifa has failed."
Can you responsibly offset carbon emissions?
Berners-Lee believes Fifa has "hideously underestimated" its carbon footprint, and that it "doesn't really work to claim you haven't had a carbon impact".
"The World Cup is very important and it is bound to have a carbon footprint. We should try to keep that as low as possible right now. You might want to move the World Cup around the world to show support for all the footballing nations, but Qatar isn't one of those.
"An example is that Fifa assumed all those [aeroplane] journeys are going to be one-way tickets, which is a complete nonsense of an assumption.
"The closest you could get to offsetting would be to find some schemes that did remove that carbon from the atmosphere, such as tree planting or restoring peat bogs.
"Fifa's claim this is the greenest World Cup ever doesn't make any sense. The idea it has somehow made it green by cheap, nasty so-called offsets that don't undo the damage from the emissions at all - to become carbon neutral, that doesn't stack up at all."
What are the 'significant environmental programs'?
A spokesperson for the Supreme Committee for Delivery and Legacy said: "Since we were awarded the right to host the tournament in 2010, sustainability has defined all our planning and operations, and it is at the heart of our legacy vision.
"Our significant environmental programs will leave a lasting legacy across the country. These include a vast new solar power plant the size of 1,300 football pitches with 800MW capacity, and stadiums which have set new standards for design and sustainability - achieving some of the highest green building certifications.
"The tree and turf nursery features a total of 679,000 shrubs and 16,000 trees, most of which are replanted across the stadium sites and other areas of the country. Many of the plants are endemic to the region and drought tolerant, which minimize the irrigation requirements. The irrigation system uses recycled water. These new trees will reduce carbon emissions.
"The compact nature of this World Cup means internal flights will not be required, and fans can travel to stadiums free of charge on the new state-of-the-art Doha Metro, supported by 750 new electric buses."