Unsustainable land use and greenhouse gas emissions are delivering a one-two punch to natural ecosystems that are key to the fight against global climate change . And without sweeping emissions cuts and transformations to food production and land management, the world stands no chance of staving off catastrophic planetary warming.

Thats according to a dire new United Nations assessment of the complex relationship between terrestrial landscapes and climate change. The report from the Intergovernmental Panel on Climate Change, or IPCC, the leading U.N. body of researchers studying human-caused global warming, warns that the unfolding crisis poses a serious threat to global food security.

Climate change has already affected food security due to warming, changing precipitation patterns, and greater frequency of some extreme events, the report says. An estimated 500 million people live in areas where once productive land has dried out and turned to desert, including North Africa, East Asia and the Middle East.

In general, climate change will cause declined yields, increased prices, reduced nutrient levels and disruptions in supply chains for food, report co-author Panmao Zhai said at a Thursday press conference in Geneva, Switzerland.