An episode of BBC's Frozen Planet wasn't going to be shown in the US because it focused on climate change.

Frozen Planet was a 2011 seven part nature documentary series about life in the Arctic and Antarctic. Though the whole series was broadcast in the UK, the final episode was optional for airing in other countries so that the show could still be sold where the issue is politically sensitive. 

The US Discovery Channel was originally not going to air the episode, but ultimately decided to air it on December 6th of that year. But the Discovery Channel wasn’t alone. 

A whole ten networks opted out of showing the episode for fear of controversy and the reaction it could draw from skeptics of climate change. An added factor was that global warming was expected to be very sensitive in the US due it thought to likely be a prominent issue in the 2012 presidential race. 

The episode, called “On Thin Ice,” discusses what shrinking glaciers and rising temperatures would mean for people and for wildlife. 

(Source)