Trying to feed the world's ever growing human population without further straining Earth's resources seems like an impossible challenge. But a new study maintains that by focusing efforts to improve food systems on a few specific regions, existing cropland could feed as much as three billion more people while also reducing agriculture's environmental footprint.

The report, published in the journal Science, focuses on 17 key crops that produce 86 percent of the world's crop calories and account for most irrigation and fertilizer consumption around the world. It proposes taking action in three broad areas that can best reduce the adverse environmental impacts of agriculture as well as boost our ability meet global food needs.

In each area, there are certain "leverage points" where nongovernmental organizations, foundations, governments, businesses and citizens can target food-security efforts for the greatest impact. China, India, the United States, Brazil, Indonesia and Pakistan - along with Europe - are the key countries with the biggest opportunity to put these proposed ideas into effect.

"This paper represents an important next step beyond previous studies that have broadly outlined strategies for sustainably feeding people," lead author Paul West, co-director of the Institute on the Environment's Global Landscapes Initiative, said in a statement.

"By pointing out specifically what we can do and where, it gives funders and policy makers the information they need to target their activities for the greatest good."

The first key leverage point is producing more food on existing land. Previous studies have detected a significant "yield gap" - the difference between potential and actual crop yield - in many parts of the world. Closing the gap just 50 percent could result in producing enough food to feed 850 million people, researchers say.

Growing crops more efficiently is also a key component. Agriculture is responsible for 20 to 35 percent of global greenhouse gas emissions, mainly from carbon dioxide release following deforestation, methane from livestock and rice growing and nitrous oxide from crop fertilization. Researchers claim that it's possible to cut back on such environmentally damaging practices without sacrificing food production.

Not only are growing crops more efficiently important, but using them efficiently is critical as well. To gain some perspective, some 30 to 50 percent of food is wasted worldwide - mostly from animal products, and mostly from the United States, China and India. The combined food wasted in all three of these countries could feed 400 million people.

"Sustainably feeding people today and in the future is one of humanity's grand challenges," West explained. "Fortunately, the opportunities to have a global impact and move in the right direction are clustered... So let's do it."