Climate scientists say the current global appetite for beef and dairy is unsustainable in the long term – but even modest changes could have a major impact.

Beef demand is rising around the world. In the U.S., per capita beef consumption has leveled off. But Americans’ growing demand for dairy products like yogurt and cheese is driving demand for more alfalfa in the Colorado River basin, said Brian Richter, the lead author of the study on Colorado River water use.

The rising global demand for beef and dairy products means there are now so many cows on the planet that they’ve become a major source of greenhouse gas emissions.