The final episode of the hit BBC nature documentary Frozen Planet is causing controversy over its depiction of climate change.

Lord Nigel Lawson has challenged Sir David Attenborough's claims, saying that "when it comes to global warming he seems to prefer sensation to objectivity".

Attenborough says in the programme that by 2020, the Arctic could be ice-free and that polar bears are dying as a result of the melting snow.

But Lord Lawson, writing in the Radio Times, said that ice cover at the other end of the world, in Antarctica, is actually broadening and that certain populations of polar bears are seeing a rise.

He added that evaporation from the melting ice would counter global warming by providing more cloud cover.

However, many experts have rallied to support the programme.

The International Union for the Conservation of Nature (IUCN) found that the majority of polar bear populations are in decline as they struggle to hunt for food where there is less sea ice.

Dr Ian Willis, a Cambridge University senior researcher, said that total sea ice in Antarctica had indeed increased slightly but that the total sea ice in the Northern hemisphere had declined overall.

He told the Telegraph that if change on this scale continues, it could be catastophic:
"If the Arctic sea ice continues to disappear it will drive up the temperature of the planet more quickly and the melting ice could drive up sea levels by one metre - enough to threaten millions of people by the end of the century."

Dr Mark Brandon, Polar Oceanographer at the Open University, is a consultant on the programme, He stood by the claims, saying that "it is a brave and honest portrayal of what is going on right now".

The episode previously caused controversy when the BBC was criticised for allowing countries to opt out of buying it, as a result a few foreign networks have decided against showing it at all.

The final episode will be broadcast on BBC One on 7 December.