Beef is unhealthy for the planet, two new studies say. One study examined beef production in the United States. The other looked at beef production around the world.

The first study was published in the scientific journal, Proceedings of the National Academy of Sciences. It compared raising beef to raising other meats such as pork or chicken.

This study found that raising beef needed 28 times more land than other meats. It also needed 11 times more water. Raising beef gives off five times more planet-warming gases than other meat production, the study said.

Maybe We Should Replace Beef

The planet-warming gases are called greenhouse gases. They are gases that can affect the Earth's temperature. They add to global warming and can hurt the environment.

"For people, the obvious answer is: whenever possible, replace beef with something else," said Gidon Eshel, lead author of the study.

"If you really need it to be from animal sources, that's still OK," Eshel said. "You can still have bacon and eggs and whatever you want. As long as it's not beef, you have always made a significant step forward."

The journal's study looked closely at beef production in the United States. It considered the effects of cows grazing. It also examined growing food for the cattle and water use.

Eshel said the study should make us change our meat choices. He also said it should influence the law.

He said it's a common problem for people to use resources "poorly and wastefully."

All Livestock Are Contributors

The other study looked at beef production around the world over the last 50 years. The results showed a huge increase in harmful gases linked to livestock such as cows. This study was published in the journal Climate Change.

Poorer countries increased the amount of greenhouse gases they create by 51 percent from 1961 to 2010. People in these countries have been eating more beef.

Wealthier countries such as the United States have been releasing fewer gases since 1970.

Beef cattle produced more than half the amount of greenhouse gases. Dairy cattle were responsible for 17 percent. Sheep, buffalo, pigs and goats each contributed less than 10 percent. The largest increases came in African countries such as Congo, the Central African Republic and Oman, the study found.

"More and more of the developing world is adopting the bad habits of the developed world," said study co-author Ken Caldeira.

The beef industry does not accept the results of these studies. Producing beef is more complicated than the scientists realize, the industry says.

"The U.S. beef industry produces beef with lower greenhouse gas emissions than any other country," it said in a response to the study.