An exhibition of the competition's best photographs opened in London's Natural History Museum on Friday.
"This picture is definitely not about composition or magical light. It is a simple message - the last polar bear on the last ice floe in a time of global warming," jury member Klaus Nigge said of Nævra's "Polar Bear".
Nævra took the picture during a sleepless night east of Barents Island in 2005.
"The boat was a long way from land and solid ice when suddenly an ice floe with an extraordinary passenger turned up. The young bear finally swam away from his melting lifeboat, but the picture clearly shows how climate change is affecting the Arctic," Nævra said.
Over 32,000 photos from 78 nations were sent in by professional and amateur photographers.
The most popular category, "Animal portraits", was won by Sergei Goskhov for his close-up of a bear in eastern Russia. Gorskhov was concentrating on capturing leaping wild salmon on camera when he suddenly noticed the bear staring at him.
