By Chris Arsenault

ROME, March 25 (Thomson Reuters Foundation) - Scientists have bred 30 new varieties of "heat-beating" beans designed to provide protein for the world's poor in the face of global warming, researchers announced on Wednesday.

Described as "meat of the poor", beans are a key food source for more than 400 million people across the developing world, but the area suitable for growing them could drop 50 percent by 2050 because of global warming, endangering tens of millions of lives, scientists said.

"Small farmers around the world are living on the edge even during the best situation," Steve Beebe, a senior bean researcher told the Thomson Reuters Foundation.

"Climate change will force many to go hungry, or throw in the towel, sell their land and move into urban slums if they don't get support."

Many of the new varieties, bred to resist droughts and higher temperatures, put traits from less popular strains, such as the tepary bean, into pinto, black, white and kidney beans.

Beebe said the new varieties were bred through traditional crossing of different species, rather than more controversial genetic engineering whereby traits are artificially transferred.

The discovery was made after scientists examined thousands of strains of beans stored in "gene banks". They were actually searching for types of beans that could withstand poor soils when they found genes to help create the "heat-beater" beans, Beebe said.

Some of the 30 new types also have higher iron content to help increase their nutritional value, CGIAR, the research group backing the new discoveries, said in a statement.

New heat tolerant beans might be able to handle average global temperature increases of 4 degrees, the medium-term worst case scenario for global warming, researchers said.

If the new strains can handle even a 3 degree rise in average temperatures, the bean production area lost to climate change would be limited to about 5 percent, they said.

Bean growers in Latin America and sub-Saharan Africa - including Nicaragua, Haiti, Brazil, Honduras, Kenya, Tanzania, Uganda, and the Democratic Republic of Congo - are likely to be the worst hit by global warming, researchers said.

Some of these countries, dependent on small farmers to feed themselves, are not in good positions to adapt to a warming planet.

Clayton Campanhola, director of plant production and protection at the U.N. Food and Agriculture Organization, said the discovery of new "climate smart" bean strains is a big deal.

"It's important to have innovation," Campanhola said. "We need to promote access to these seeds for small farmers... it's an major achievement."

(Reporting By Chris Arsenault, editing by Alisa Tang)