SIR – Environmentalists tell us that sea temperatures are rising but David Attenborough in his Frozen Planet series said that the water beneath the frozen sea in the polar regions is still at -2C as it has been for 23 million years.

The ice will stop temperatures plummeting but how has it maintained the same temperature for so long?

Perhaps Keith Thomson of T&A’s Enviro Watch knows the answer. I am at sea.

David Rhodes, Croscombe Walk, Bradford