Dunfermline-born Doug Allan said: "There's a tragic lack of assertive political and economic incentives to do anything about global warming. The only thing that will work would be truly global initiative. But it won't be easy. It will mean people recognising humans are still part of nature, not lords over it, and accepting we need a more sustainable lifestyle."

Environmental experts describe this year's shrinkage of the Arctic sea ice as "unprecedented", and as a clear sign of continuing climate change, stemming from rising levels of CO2. This year's sea ice cover was 700,000 sq km below the previous minimum of 4.17 mil- lion sq km, set in 2007.

Many scientists who fear the Arctic Ocean's summer ice may disappear by 2020 believe the world has a "planetary emergency" on its hands.

Mr Allan, who has worked in the Arctic on television documentaries including Frozen Planet, Planet Earth, Life and The Blue Planet, said: "Actually, 2020 might even become an optimistic date. The latest generation of satellites has discovered not only that the ice area is shrinking but the actual ice thickness is decreasing.

"Ten years ago, most climate-change scientists predicted an ice-free summer sometime in the next 50 years. Today, a number think it will happen within five years.

"That means that within the next five years, there will be a year when effectively all the Arctic sea ice will melt in the summer, and that will herald a whole new baseline. The chances of it then melting every summer will be greater. Mathematical models come up with scary scenarios of what this could mean. The possible outcomes are almost beyond our imagination."