Scientists say they have evidence that the powerful greenhouse gas methane is escaping from the Arctic sea-bed.

Researchers say this could be evidence of a predicted positive feedback effect of climate change.

As temperatures rise, the sea-bed grows warmer and frozen water crystals in the sediment break down, allowing methane trapped inside them to escape.

The research team found that more than 250 plumes of methane bubbles are rising from the sea-bed off Norway.

The joint British and German research team detected the bubbles using a type of sonar normally used to search for shoals of fish. Once detected, the bubbles were sampled and tested for methane at a range of depths.

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