WASHINGTON  —  With climate change increasingly threatening the survival of plants and animals, scientists say it may become necessary to move some species to save them.

Dubbed assisted colonization or assisted migration, the idea is to decide how severe the threat is to various species, and if they need help to deal with it.

"When I first brought up this idea some 10 years ago in conservation meetings, most people were horrified," said Camille Parmesan, a biology professor at the University of Texas.

"But now, as the reality of global warming sinks in, and species are already becoming endangered and even going extinct because of climate change, I'm seeing a new willingness in the conservation community to at least talk about the possibility of helping out species by moving them around," she said.

Parmesan discusses the idea in Friday's edition of the journal Science.

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It's an idea that makes conservation biologists nervous.

There are plenty of risks in moving plants and animals to new locations. They may not survive, or they may become invasive, growing wildly without predators and crowding out natives of their new location.

And it's not possible to relocate every species that may need it, so how to decide who gets moved and who gets left behind to become extinct?

Stanford biologist Terry Root has been traveling the country urging her colleagues to come up with a plan for "triage" to decide which species should be saved from global warming and which can't.

After other biologists complained about the word "triage," Root said she now calls it prioritizing which species should be saved.

"We've got to work on the ones we have a prayer of saving," Root said.

Some species will have to be written off, she suggested, such as threatened and endangered species of the "sky islands" in Arizona and New Mexico because "they don't have any place to move to."

"Those species are functionally extinct right now," Root said. "They're toast."

When deciding which species to save and which to watch die, Root said one key is uniqueness.

That's why she said she'd save the odd-looking tuatara of New Zealand, a lizard-like creature with almost no living relatives, over the common sparrow.

The risk of extinction has to be balanced by the potential hazard to the community where a species is relocated as well as the time and cost of making the move, Parmesan says.

"Ultimately, the decision about whether to actively assist the movement of a species into new territories will rest on ethical and aesthetic grounds as much as on hard science," she said in a statement.

"Passively assisting coral reef migration may be acceptable, but transplanting polar bears to Antarctica, where they would likely drive native penguins to extinction, would not be acceptable," she said.

"Conservation has never been an exact science, but preserving biodiversity in the face of climate change is likely to require a fundamental rethinking of what it means to preserve biodiversity," Parmesan said.

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