Scientists and companies working to grow meat from animal cells will need to minimise energy use and avoid fossil fuels if claims that cultured meat is better for the climate than real meat are to hold true, researchers said.

Cultured meat production with high energy inputs could spur global warming more in the long-term than some types of beef cattle farming if the world shunned a low-carbon path, said a study published on Tuesday by the UK-based Oxford Martin School.

Lead author John Lynch, a researcher at the University of Oxford, said reducing beef consumption would help curb climate change, as methane emitted by cattle is a potent heat-trapping gas. But how best to replace conventional meat remained unclear.

"We have to dig into the details a bit more to know if the substitutes would be as beneficial as claimed," he told the Thomson Reuters Foundation. "It just comes down to how much energy demand would be to produce a kilogramme of meat."

Lynch said companies promising to bring lab-grown "clean" meat to the mass market, many of them based in the United States and Israel, had yet to release information on their planned large-scale production processes.

The website of one high-profile firm, Memphis Meats, which produced the world's first cell-based meatball in 2016 followed by poultry in 2017, says its meat, cultivated "at scale", would use significantly less land, water, energy and food inputs.

"Our process will produce less waste and dramatically fewer greenhouse gas emissions. We believe that the planet will be the ultimate beneficiary of our product," it adds, without giving details of how that would be achieved.

Memphis Meats has received investment from business tycoons Bill Gates and Richard Branson, as well as multinational corporations Cargill and Tyson Foods.

David Welch, director of science and technology at The Good Food Institute, a nonprofit that supports early-stage companies producing "clean" meat, said it would likely be another five to 10 years before cultured meat products were commercially available to consumers.

Development work was still being carried out in labs, with production facilities yet to be set up, he added.

The Oxford Martin School study said research on greener ways of producing cultured meat was a priority at this nascent stage.

Its study used four hypothetical cultured meat production methods, concluding the most energy-efficient would not warm the planet more than farming beef in the long term, even without decarbonisation of the global energy system.

"If the real (clean meat) production processes are like that one, then there is no problem," said Lynch.

Livestock are responsible for about 14.5 percent of global greenhouse gas emissions, according to the United Nations' Food and Agriculture Organization.

The Good Food Institute plans this year to carry out an in-depth study of the environmental effects of cultured meat production with companies, to deepen understanding of the risks and benefits, including for land, water and the climate.

METHANE VERSUS CO2

The Oxford research highlighted a huge difference in the amount of time for which different greenhouse gases influence the climate. Methane, released from cattle manure and flatulence, is more dangerous in the short-term but fades fast.

"Per tonne emitted, methane has a much larger warming impact than carbon dioxide - however, it only remains in the atmosphere for about 12 years whereas carbon dioxide persists and accumulates for millennia," said study co-author Raymond Pierrehumbert, a physics professor at the University of Oxford.

As a result, the researchers found over a 1,000-year period, production of cultured meat could hike global warming more if the process depended heavily on high-carbon energy.

Another important factor was land use, they said.

For example, clearing forest land for cattle-grazing could greatly increase the carbon footprint of beef production, while growing meat in urban laboratories could free up land for storing carbon in vegetation or other ways.

A separate paper from London-based think tank Chatham House said on Tuesday cultured meat had the potential to contribute to the emissions-reduction goals of the European Union, but policy makers would need to promote clear regulation and invest public funds in research, development and commercialisation.