McDonald's pledged Tuesday to start buying verified sustainable beef, but it's going to take awhile.

"Our goal is to purchase sustainable beef by 2016," wrote Becca Hary, a director of global media relations at McDonald's, in an email. "Some areas of the world are more advanced when it comes to traceability capabilities, and it is likely that our first purchases will come from one of those areas. We will focus on increasing the annual amount each year, but it is too early to predict the quantity that will be purchased in 2016.