Frozen Planet is a nature documentary series, co-produced by the BBC, the Discovery Channel and The Open University. It was filmed by the BBC Natural History Unit. Other production partners are the Discovery Channel Canada, ZDF, Antena 3 and Skai TV. The production team, which includes executive producer Alastair Fothergill and series producer Vanessa Berlowitz, were previously responsible for the award-winning series The Blue Planet and Planet Earth, and Frozen Planet is billed as a sequel of sorts. David Attenborough returns as narrator. The seven-part series focuses on life and the environment in both the Arctic and Antarctic. The production team were keen to film a comprehensive record of the natural history of the polar regions, because climate change is affecting landforms such as glaciers, ice shelves, and the extent of sea ice. The film was met with critical acclaim and holds a Metacritic score of 90/100. Despite such, it has been criticized for limited coverage of the effects of global warming and attribution of recent climate change. Whilst the series was broadcast in full in the UK, the BBC chose to make the series' seventh episode, which focuses on climate change, optional for syndication in order to aid sales of the show in countries where the issue is politically sensitive. The US Discovery Channel originally announced that they would air only the first six episodes of the show, but they later added the seventh episode to their schedule.