Frederique Olivier / Adelie penguin (Pygoscelis adeliae) colony, with icebergs and pack ice in the background, Antarctica.

Frederique Olivier / Adelie penguins (Pygoscelis adeliae) diving, seen from underwater, Antarctica.

Ingo Arndt / Emperor penguins (Aptenodytes forsteri) Weddell Sea, Antarctica

Danny Green / Three Sea otters (Enhydra lutris) resting on ice, Alaska, June

Brent Stephenson / Sunset off Scott Island, with floating pieces of sea ice, Scott Inlet, Baffin Island, Canadian Arctic, August 2015.

Sven Zacek / Broken ice covered in snow at sunset, on the shore of Lake Vortsjarv, gathered to shore by extreme winds, Estonia. December 2014.

Bryan and Cherry Alexander / Chinstrap penguins (Pygoscelis antarctica) on a blue iceberg, with Antarctic Prion (Pachyptila desolata) flying over. Antarctica

Ben Cranke,Ben Cranke / Gentoo Penguin (Pygoscelis papua) penguins rest on a floating iceberg, Antarctic Peninsula, Antarctica

Ben Cranke,Ben Cranke / Gentoo Penguin (Pygoscelis papua) group travelling out to sea, Cuverville Island, Antarctic Peninsula, Antarctica

Orsolya Haarberg / Arctic tern (Sterna paradisaea), adult feeding young. Jokulsarlon glacial lagoon. Iceland. August 2008

Steven Kazlowski,Steven Kazlowski / Polar bear (Ursus maritimus) curious adult head underwater, Beaufort Sea, off the 1002 area of the Arctic National Wildlife Refuge, North Slope, Alaska.

Steven Kazlowski,Steven Kazlowski / Polar bear (Ursus maritimus) 4-5 year-old on pack ice, low angle shot, off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Beaufort Sea, autumn