Geologists, biologists and other scientists convened Thursday in Paris to discuss how to stop the spread of fungus stains — aggravated by global warming — that threaten France's prehistoric Lascaux cave drawings.

Black stains have spread across the cave's prehistoric murals of bulls, felines and other images, and scientists have been hard-pressed to halt the fungal creep.

Marc Gaulthier, who heads the Lascaux Caves International Scientific Committee, said the challenges facing the group are vast and global warming now poses an added problem.

This makes sending teams of scientists into the affected caverns risky, as their mere presence raises humidity levels and temperatures that could contribute to the growth of the different fungi, algae and bacteria that have attacked the cave over the years, he said.

Other factors behind the stains include the presence of naturally occurring microorganisms and the chemical makeup of the rock that forms the cavern walls, Gaulthier and other scientists at the news conference said.

For the moment, the cave is completely sealed in hopes that "it will heal itself," Gaulthier said.