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In 2002, the world's governments agreed to significantly slow the rate of biodiversity loss by 2010. Time is almost up, and by most accounts they've failed. Now that climate change is emerging as one of biodiversity's greatest threats, scientists are proposing new ways to tackle the crisis鈥� Others aren't convinced of the merits of assisted migration. 鈥淚t's ecological gambling,鈥� says Anthony Ricciardi, an invasive-species biologist at McGill University in Montreal. 鈥淲e do not have a sufficient understanding of the impact to engage safely in assisted colonization on a frequent basis.鈥� The risks aren't empty. Whether the species in question is an American pica or a torreya pine, its intentional introduction could transfer disease into new host species, or it could become invasive and wipe out the destination's native fauna.