A new report from the United Nations says changing diets to eat more plant-based foods and changing farming to sustainable livestock management could reduce carbon emissions by 0.7 to 8.0 gigatonnes a year.
It could also free up several million square kilometres of land by 2050.
But if nothing changes, there will be global warming, food insecurity, threats to health and a reduction in biodiversity.
The report said global population growth and changes in consumption patterns have caused unprecedented rates of land and water use and that trend is not sustainable.
The report was prepared by the United Nations' Intergovernmental Panel on Climate Change; it has been issuing dire warnings about global warming for decades.
"Delaying action ... could result in some irreversible impacts on some ecosystems, which in the longer term has the potential to lead to substantial additional emissions from ecosystems that would accelerate global warming," the panel’s report said.