More than 60 scientists from 11 countries have signed an open letter calling for governments around the world to cut the quantities of meat and dairy served in schools and hospitals.

The letter urges mayors to do their bit by reducing animal products in public canteens as part of a move to “maintain a safe climate and planet for the future of humanity”.

Currently, livestock emissions – including the associated deforestation impacts – account for 14.5 per cent of global greenhouse gas emissions. This is equivalent to all cars, trains, ships and aircraft combined.

The letter says a sixth of the carbon footprint of average diets in Europe is due to tropical deforestation emissions. Reducing demand for meat and dairy products as well as reducing food waste will be critical in addressing the climate crisis, scientists say.

Professor Pete Smith from the University of Aberdeen, a lead author of reports by the UN’s Intergovernmental Panel on Climate Change (IPCC), spearheaded the letter.

He said: “Eating less meat and dairy in our growing cities is a way to address the climate emergency. Cities can play a crucial role in helping citizens to reduce their consumption of livestock products, and to enable the changes necessary to meet ambitious climate change targets.”

Greenpeace International spokesperson Reyes Tirado said: “Mayors are in charge of millions of meals every day. They should do everything in their power to create a healthy future for both citizens and the planet.”

Extinction Rebellion: Climate change protests cause chaos in London Show all 46 1 /46 Extinction Rebellion: Climate change protests cause chaos in London Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf A protester gives a thumbs up as he stalls a DLR train at Canary Wharf station in London Reuters Extinction Rebellion: Climate change protests cause chaos in London City of London Protesters hold up traffic on Upper Thames Street in the City of London Getty Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf Protesters hold a banner as they hold up a DLR train at Canary Wharf station in London Reuters Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Officers remove plants that were placed in the occupation of Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Police officers arrive at Oxford Circus as they prepare to remove protesters during the fifth day of a coordinated protest by the Extinction Rebellion group, April 19 Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge An activist waters the plants at the occupation on Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Heathrow airport Undeterred by over 400 arrests, climate change activists continued their demonstration into a fifth day in London with a small protest at the country's main Heathrow Airport, along with the ongoing protest camps at other iconic locations around the British capital Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Protesters with the words 'glued on' written on their hands hold hands as police officers arrive at Oxford Circus Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Officers circle the lorry that serves as the central stage to the Waterloo Bridge occupation, repeating their tactic from a earlier at the Oxford Circus occupation Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Oxford Circus reopens after being closed for days due to occupation AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Officers prepare to move in on the occupation of Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Activists relax on a sofa at the occupation on Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus British actress Emma Thompson talks to members of the media from atop the pink boat after police officers surrounded the boat being used as a stage as climate change activists occupy the road junction at Oxford Circus in central London during the fifth day of environmental protesst by the Extinction Rebellion group AFP Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge An Extinction Rebellion demonstrator is carried away by police on Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Activists on Waterloo Bridge have made a garden for their occupation site, April 20 Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Demonstrators began blocking off a bridge and major central road junctions on April 15 at the start of a civil disobedience campaign calling for governments to declare an ecological emergency over climate change, to reduce greenhouse gas emissions to zero by 2025, halt biodiversity loss and be led by new "citizens' assemblies on climate and ecological justice" Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Emma Thompson joins the Extinction Rebellion protest at Oxford Circus. Thompson spoke from the pink boat at the centre of the occupation AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Heathrow airport Extinction Rebellion protesters sit outside Heathrow Airport on April 19 Reuters Extinction Rebellion: Climate change protests cause chaos in London Heathrow airport Climate protestors hold a demo outside Heathrow Airport Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Police officers detain a climate change activist at Waterloo Bridge Reuters Extinction Rebellion: Climate change protests cause chaos in London Marble Arch Protesters prepare for another day at Marble Arch as the Extinction Rebellion protests enter their fifth day Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus British actress Emma Thompson gives an address from the stage atop the pink boat AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Actress Emma Thompson takes a photo with a Extinction Rebellion demonstrator PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Climate change activists blockade Oxford Circus on the third day of an environmental protest by the Extinction Rebellion group AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Climate change activists stand atop a bus shelter as they take part in a blockade of Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf Police is seen as climate change activists demonstrate during the Extinction Rebellion protest, at Canary Wharf DLR station in London Reuters Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Police speak to climate change activists blockading Waterloo bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge epa07511673 A demonstrator gestures the hand heart as protesters from the Extinction Rebellion campaign group block Waterloo Bridge in central London, Britain, 17 April 2019. The Extinction Rebellion are holding a number of protests across London to draw attention to climate change. EPA/NEIL HALL NEIL HALL EPA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Climate change activists, one (right) with her hand glued to the underside of a truck parked across Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Environmental campaigners protest in the centre of Oxford Circus Getty Extinction Rebellion: Climate change protests cause chaos in London Jeremy Corbyn's Home Climate change activists from Extinction Rebellion protest sit after glueing themselves to the front fence of Britain's opposition Labour Party leader Jeremy Corbyn's house Reuters Extinction Rebellion: Climate change protests cause chaos in London Marble Arch Dozens of tents have been pitched at Marble Arch in a large scale occupation Reuters Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf station Police remove climate activists who glued themselves on top of a train at Canary Wharf station EPA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Police forces carry a protester AP Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf station A climate change protestor who glued his hand to a window halts a DLR train AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Extinction Rebellion demonstrators on Waterloo Bridge, London, after police issued a Section 14 Public Order Act 1986 warning. PRESS ASSOCIATION Photo. Picture date: Wednesday April 17, 2019. See PA story ENVIRONMENT Climate. Photo credit should read: Jonathan Brady/PA Wire Jonathan Brady PA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge epa07512336 Extinction Rebellion climate change demonstrators protest on Waterloo Bridge during climate change protests in London, Britain, 17 April 2019. The Extinction Rebellion are holding a number of protests across London to draw attention to climate change. EPA/ANDY RAIN ANDY RAIN EPA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge epa07512368 Extinction Rebellion climate change demonstrators protest on Waterloo Bridge during climate change protests in London, Britain, 17 April 2019. Waterloo Bridge remains closed as protests continue. EPA/ANDY RAIN ANDY RAIN EPA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Extinction Rebellion demonstrators in Oxford Circus, London, as more than 200 people have been arrested as police deal with ongoing climate change protests. PRESS ASSOCIATION Photo. Picture date: Wednesday April 17, 2019. See PA story ENVIRONMENT Climate. Photo credit should read: Kirsty O'Connor/PA Wire Kirsty O'Connor PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus LONDON, ENGLAND - APRIL 17: An Environmental campaigner is carried by police officers at Oxford Circus during the third day of a coordinated protest by the Extinction Rebellion group on April 17, 2019 in London, England. More than 100 arrests have been made, with demonstrations blocking a number of locations across the capital. (Photo by Leon Neal/Getty Images) Leon Neal Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Pedestrians and a cyclist pass graffiti drawn by protestors who blocked Waterloo Bridge AP Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Climate change protestors practice yoga on Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge A climate change activist gestures while being detained by police officers Reuters Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Protestors sit on the road AP Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Extinction Rebellion demonstrators on Waterloo Bridge, London, as more than 200 people have been arrested as police deal with ongoing climate change protests. PRESS ASSOCIATION Photo. Picture date: Wednesday April 17, 2019. See PA story ENVIRONMENT Climate. Photo credit should read: Yui Mok/PA Wire Yui Mok PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Police forces carry a protestor to arrest him at Oxford Circus in London, Wednesday, April 17, 2019. The group Extinction Rebellion is calling for a week of civil disobedience against what it says is the failure to tackle the causes of climate change. (AP Photo/Frank Augstein) Frank Augstein AP

Last year, researchers from the University of Oxford found cutting meat and dairy products out of an individual’s diet reduced their carbon footprint by up to 73 per cent.

They also found the amount of farmland used could be reduced by 75 per cent, an area equivalent to the size of the US, China, Australia and the EU combined.

Ms Tirado said: “The greenhouse gas footprint of plant-based foods is up to 100 times less than of animal products.

“Shifting to plant-based foods is also a way to help protect the world’s forests, such as the Amazon. By decreasing the bulk demand for meat, and thus also for feed, cities can make a tremendous difference regarding their carbon and deforestation footprint.

“We can still limit global temperature rise to 1.5 degrees above pre-industrial levels, but we need quick action.”

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According to an EAT-Lancet report, humanity needs to reduce its meat intake by around 90 per cent to stay within sustainable limits. The World Cancer Research Fund recommends avoiding processed meat altogether due to its carcinogenic properties.

City leaders around the world are increasingly creating ambitious food policies.

New York City mayor Bill de Blasio has announced that all 1,700 public schools in the city will serve meatless meals every Monday.

And in Mexico, the “Come Consciente” programme requires all schools in Veracruz (Mexico’s second-largest state) to serve plant-based meals on Mondays.

The letter was written ahead of the Milan Urban Food Policy Pact (MUFPP) annual gathering in Montpellier and the C40 World Mayors Summit in Copenhagen.