A growing, more affluent population competing for ever scarcer resources could make for an "unrecognizable" world by 2050, researchers warned at a major U.S. science conference Sunday.

The UN has predicted the global population will reach seven billion this year, and climb to nine billion by 2050, "with almost all of the growth occurring in poor countries, particularly Africa and South Asia," said John Bongaarts of the non-profit Population Council.

To feed all those mouths, "we will need to produce as much food in the next 40 years as we have in the last 8,000," said Jason Clay of the World Wildlife Fund.

"By 2050 we will not have a planet left that is recognizable" if current trends continue, Clay said.