The demand for chocolate increases by about 2.5 to 3 percent each year, which means about four million more tons of cocoa are needed every year.

Experts predict that by 2020, the demand for chocolate will increase by 25 percent. That's about five million metric tons of chocolate.

"Cocoa has been almost completely static," said Andrew Pederson, global chocolate manager for Mars, Inc., the makers of M&Ms, Milky Way bars, Snickers and other confections. "The crops don't perform well. They're aging pretty badly. Farmers don't have a lot of tools and training."

Existing cocoa plants, mostly in tropical countries, are old and worn out, and it is difficult to find space to plant more. Expansion of cropland could mean deforestation.

"Cocoa is a crop that is fragile. Cocoa is a crop that is very picky where it likes to grow," Peck said. "It needs tropical, humid conditions with rich soil. There's not a lot of land availability with those conditions around the world."

Experts say newer and stronger cocoa plants need to be developed to keep up with demand, which can take years.