Western countries like New Zealand need to cut their beef and pork consumption by 90 percent if humanity is to survive the next century, according to scientists.
And they say a meat tax might be the best way to achieve it.
According to a new study, by 2050 the environmental costs of present-day food production will almost double, as the Earth's population rockets to 10 billion and more of the world is lifted out of poverty and switch to meat-rich diets.
"It is pretty shocking," study leader Marco Springmann of the University of Oxford told The Guardian. "We are really risking the sustainability of the whole system. If we are interested in people being able to farm and eat, then we better not do that."
The study, published in journal Nature, says "in the absence of technological changes and dedicated mitigation measures", pollution and resource depletion will reach "levels that are beyond the planetary boundaries that define a safe operating space for humanity".
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It takes vastly more resources to produce meat than it does plant food, and generally causes more pollution. Meat only provides a fifth of the world's calories but takes up 83 percent of farmland and accounts for half of the agricultural sector's greenhouse gas emissions.
The study estimates the average world citizen would need to cut their consumption of beef by 75 percent, pork by 90 percent and eggs by 50 percent, made up for by tripling their intake of beans and eating four times' the amount of nuts and seeds.
The average Westerner has a lot more to give up - we need to eat 90 percent less beef and 60 percent less milk, and up our bean intake by 700 percent.
The researchers say policy makers need to do more to change people's eating habits, because they're unlikely to themselves.
"The available evidence suggests that providing information without additional economic or environmental changes has a limited influence on behaviour, and that integrated, multicomponent approaches that include clear policy measures might be best suited for changing diets," the study reads.
"Those can include a combination of media and education campaigns; labelling and consumer information; fiscal measures, such as taxation, subsidies, and other economic incentives; school and workplace approaches; local environmental changes; and direct restriction and mandates."
A University of Otago study earlier this year found few consumers knew or cared about meat's impact on the environment.
"People don't fully understand how many impacts meat consumption has on the planet, and also the severity of those impact," PhD student Garrett Lentz said.
People were far more likely to not buy meat if it was expensive or they understood the health benefits of avoiding it, that study found.
Climate Change Minister James Shaw in June begged for Kiwis to eat less meat, saying there was no risk to New Zealand's vital primary industries because of the growing demand for meat and dairy overseas.
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Beef is the biggest offender according to a 2014 study, requiring 28 times more land and 11 times more water than poultry and pork, and producing five times the emissions.
Other foods Westerners need to cut down on to save the world, according to the latest research, include poultry, lamb and sugar.
Fonterra declined to comment. NZ Beef & Lamb said it was focused on "quality over quantity and on producing more from less".
"For example, we have already reduced our absolute greenhouse gas emissions from livestock by 30 percent since 1990 while maintaining similar levels of production from fewer animals and doubling the value of our exports," said chief insight officer Jeremy Baker.
"New Zealand's sheep and beef farms are globally unique in their environmental footprint thanks to our pasture-based, free range systems. Compared to overseas red meat production methods which are often grain-based, our sheep and beef farms are very low input, using little or no extracted water, have low rates of fertiliser use, and are well matched to the capability of the land they use."
He said reducing methane emissions about 10 percent will let New Zealand "buy time" to address the "larger" threat of fossil fuels.