People should halve the amount of meat they eat as part of efforts to cut pollution caused by nutrients such as nitrogen, experts have said.
Nitrogen and other mineral fertilisers are key to feeding the world's population but burgeoning use of nutrients is causing water, land and air pollution which harms human health, oceans and wildlife, and contributes to climate change, they claimed.
Use of the minerals is expected to increase by up to 50% over the next 40 years, causing more pollution and damage to habitats, and more greenhouse gases, according to a report for the United Nations Environment Programme.
But improving the efficiency of the way nutrients are used by 20% by 2020 could reduce the annual use of nitrogen and save the world about £110 billion a year, in reduced fertiliser use and reductions in the cost to human health and the environment, the study said.
One of the main sources of pollution of minerals is agriculture. Around four-fifths of the nitrogen and phosphorus applied in farming is consumed by livestock rather than directly by humans, and about 70% of the world's agricultural land is used for producing meat and dairy.
By reducing the amount of meat they eat, people could help reduce pollution. Report lead author Professor Mark Sutton, of the Centre for Ecology and Hydrology in the UK, said: "People say we need nitrogen to feed people, actually we need nitrogen to feed our high livestock population."
The experts did not call for people to become vegetarian, but for people in countries such as the UK where meat consumption is excessive to reduce their intake, for example by having smaller portions, wasting less or eating meat less often.
Prof Sutton warned: "South East Asia, China and India are racing to catch up with levels we're eating. Our choices we're making in Europe are influencing the cultural aspirations in those places."
He said a good aim was to be demitarian, halving the amount of meat normally eaten. This would also benefit health, as Europeans currently consume 70% more protein per day on average than is needed.
The experts also recommended more localised systems of farming, where crops and livestock are grown and reared closer together so that, for example, the fertiliser created by manure can be used more efficiently to grow crops, rather than being wasted and causing pollution.