Steven Kazlowski / Polar bear (Ursus maritimus) investigating camera on pack ice off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Beaufort Sea, autumn

Steven Kazlowski / Polar bear (Ursus maritimus) investigating camera on pack ice off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Beaufort Sea, autumn

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

Paul Harcourt Davies,Paul Harcourt Davies / Low lying cloud / mist over the Piano Grande in the early morning, Sibillini, Norcia, Italy, June 2010

Niall Benvie / Cloud formations lit by low sun. Brechin, Angus, Scotland, December 2012.

Niall Benvie,Niall Benvie / Stratus and cirrus clouds above the Isle of Coll. Scotland, August 2012.

Niall Benvie,Niall Benvie / Alto cumulus clouds. Angus, Scotland, August 2012.

Michael Pitts,Michael Pitts / Sooty Terns (Onychoprion fuscata) flock in flight, Midway Island. Central Pacific.

Franco Banfi / Blue shark (Prionace glauca) viewed from below, with Snell's window effect, Pico Island, Azores, Portugal, Atlantic Ocean

Floris van Breugel / Tiny thimble jellyfish (Linuche unguiculata) drift with the current in the calm turquiose waters of a lagoon in Ofu, American Samoa. The window of sky is called Snell's Window, caused by refraction of...

Christophe Courteau / Audierne Bay in storm at low tide, Brittany, France

Ernie Janes / Holkham beach at low tide, Norfolk, UK August