Global warming is already changing rain and snow patterns and acidifying the oceans, all of which put a strain on ecosystems, scientists say.
(Related: "Warming May Spur Extinctions, Shortages, Conflicts, World Experts Warn" [April 6, 2007].)
Before any moves are made, however, rules need to be set for how plants and animals will colonize new lands across state or national boundaries, according to Thomas.
"Then we should proceed with a few [species movements] within the next ten years," Thomas said.
"Starting early means that existing populations are still large," he added. "It gets much harder to achieve once only a few individuals are surviving."
The endangered quino checkerspot butterfly "is a perfect candidate for assisted migration" to higher altitudes, said biologist and paper co-author Carmille Parmesan of the University of Texas in Austin.
The unaggressive butterfly is unlikely to overwhelm the plants it eats or crowd out other insects, Parmesan said.
"I wouldn't advocate moving them very far, as if you take a species completely out of it's evolutionary background it can become a huge pest in the new area," she added.
Corals are also ideal, since many species are at high risk and it's hard for them to change habitats quickly on their own.
Placing concrete blocks on the seafloor could give corals a boost in new areas they weren't previously able to colonize, Parmesan said.
But some consider assisted colonization to be an extreme undertaking.
Patrick Gonzalez is a climate change scientist at the Arlington, Virginia-based conservation group the Nature Conservancy.
"We need to employ the range of potential adaptation strategies before considering assisted migration, which is a relatively drastic option of last resort," Gonzalez said.
These other strategies include creating wildlife refuges and corridors to connect patches of land, allowing animals to move freely between them.
(Read: "First Evidence That Wildlife Corridors Boost Biodiversity, Study Says" [September 1, 2006].)
Others say that the practice may favor preserving individual species over whole ecosystems.
Jason McLachlan, an ecologist at Notre Dame University in Indiana, has studied assisted colonization but was not a co-author of the new paper.
"Widespread imposition of assisted migration favors saving species at the expense of saving the natural processes that shape ecosystems and landscapes," McLachlan said.
While assisted migration may save some species, McLachlan said, "there are legal, ethical, aesthetic, and emotional dimensions to the native [plants and animals] of a place."
"We need to rethink conservation in a world that is changing," said Dov Sax of Brown University in Providence, Rhode Island, who studies invasive species.
Moving species to new locations will change or disrupt the existing ecosystems to some degree, Sax said.
"In many cases we can keep these disruptions from causing environmental catastrophes, but occasionally we'll get it wrong," he said.
"The real issue in my mind is whether we can keep the ratio of successes versus catastrophes high enough to make assisted migration worthwhile," he added. "I suspect that we can."
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