Many indigenous languages have no words for legions of new animals, insects and plants advancing north as global warming thaws the polar ice and lets forests creep over tundra.
"We can't even describe what we're seeing," said Sheila Watt-Cloutier, chairwoman of the Inuit Circumpolar Conference, which says it represents 155,000 people in Canada, Alaska, Greenland and Russia.
In the Inuit language Inuktitut, robins are known just as the "bird with the red breast," she said.
Inuit hunters in northern Canada recently saw some ducks but had not figured out what species they were, in Inuktitut or any other language.
In Arctic Europe, birch trees are gaining ground and Saami reindeer herders are seeing roe deer or even elk, a forest-dwelling cousin of moose, on former lichen pastures.
The lack of words to describe newcomers does not stop at animals and plants. Words, such as thunderstorm don't exist because they are phenomena indigenous peoples have never known.