Scientists have long warned that climate change and other threats will require relocating some endangered species outside their historic ranges. Now, U.S. officials are proposing rules that would enable them to use this new — and potentially controversial — conservation tool.

Previous periods of rapid warming millions of years ago drastically altered plants and forests on Earth. Now, scientists see the beginnings of a more sudden, disruptive rearrangement of the world’s flora — a trend that will intensify if greenhouse gas emissions are not reined in.