Livestock accounts for about 20 per cent of global greenhouse gas emissions. A new study published in the journal Proceedings of the National Academy of Sciences has found the most effective way to reduce the environmental impacts of ours diet is to minimize our beef consumption.

DW: What was the most surprising result from your study?

Ron Milo: The most surprising finding was that dairy had a comparable environmental impact to pork or poultry. We found that milk has a similar impact on the environment per calorie or per protein as all meat types, except beef. Beef is much worse.

What makes beef so much worse?

This relates to the physiology and biology of cows. The process of gaining weight and creating meat is much slower than way with chickens or pigs. This has a big effect on the overall efficiency.

So how much worse for the environment is eating beef than other meats such as chicken or pork?

There's about 20-30 times more land used in order to grow the grains or grass that's fed to cattle. Beef requires about 10 times more irrigation water and produces about five times more greenhouse gas emissions and fertilizer than all the rest. Whereas the others - poultry, dairy, pork and eggs - are quite comparable to each other.

What about eating plants versus eating meat? What is the climate impact of growing something like potatoes or corn?

For beef, you need to use around 200 square meters for more than a year to get one kilo of beef. Whereas, for staple plants it would be one to three square meters. We're talking a factor of about 100 fold.

What about when meat raising is done in a sustainable way like using pastures for grass fed cattle? Don't those methods actually help to take carbon out of the environment?

There's a lot of variability. What we've found is there's usually a very strong trade-off with the different ways to grow. That is, techniques which would be more efficient in terms of greenhouse gases require more pasture land, thus affecting biodiversity. So, it seems like in each of the different cases there are high associated costs.

As the world's population continues to grow, will we be able to continue eating meat in 10 or even 50 years?

If current trends persist, there will be more and more beef and other types of meat, and this is going to be very challenging for our planet to supply the feed to all these animals. That is why we thought this study was important, because it has enabled us to tell what is more efficient. It enables us to make better decisions both as people, in terms of our diet, as well as policy makers.

Ron Milo is an associate professor at the Weizmann Institute of Science in Israel and is a co-author of the study, “Land, irrigation water, greenhouse gas and reactive nitrogen burdens of meat, eggs and dairy production in the United States.” The report was published in July in the journal, PNAS. The study was conducted in conjunction with Prof. Gidon Eshel of Bard College in the United States.