Polar tourists watch icy world melt

Activists say witnesses can help sound alarm about global warming's upheaval

They go to paddle between glistening icebergs or ski on blinding white ice, but a rising number of polar tourists get to see something else, too: the monumental changes wrought by global warming.

Polar vacationers see the ice shelves and soaring glaciers thaw before their eyes, making them important witnesses to a threatened landscape, activists and tour companies say.