A team of international scientists says global warming could drive more than a third of the wildlife in the world’s most ecologically sensitive areas to extinction by 2050 — and have similar, if less devastating, effects on plants and animals worldwide.

The researchers say increasing temperatures will make it impossible for many plants and animals to fight for shrinking habitats in the Amazon, Australia, Africa and Mexico.

“It’s a wake-up call for conservationists and biologists that climate change is potentially having a dramatic effect on wildlife, especially when you consider the loss of habitat worldwide,” said Lee Hannah, a co-author of the study and researcher with Conservation International in Washington, D.C.

The research, published in today’s issue of Nature, is expected to rekindle scientific and political debates about the costs of global warming.

“I think the point is to get people talking about the fact that we’re standing at the brink of a massive extinction, and we have to start thinking about what that means,” said Terry Root, an ecologist at Stanford University’s Center for Environmental Science and Policy. “I think it’s a fantastic study.”

But some experts said there were too many unknown factors to predict results 50 years from now.

“You have to take the numbers they give with a grain of salt,” said Lewis Ziska, a weed expert with the U.S. Agricultural Research Service in Beltsville, Md., who studies the effects of climate change on invasive plants that damage crops.

The researchers used computer projections to estimate future populations of 1,103 native plants, birds, butterflies, frogs and other animals in hotspots from the Amazon rain forests of Brazil to the hills of Scotland and the Australian outback. Together, the areas they studied account for about 20 percent of the Earth’s surface, the researchers said.

The team, from the United States, England, Mexico, Australia, Brazil and South Africa, stopped short of predicting the extinction of any particular plant or animal. But the researchers said the species most threatened, including Australian reptiles, European songbirds, depend on shrinking habitats.