COP26: The Ocean - why our seas hold the key to tackling climate change

Ahead of the COP26 climate summit, endurance swimmer Lewis Pugh takes us into icy - but warming - Arctic waters; UN envoy Peter Thomson calls on world leaders to act urgently to protect the ocean. And we head to the swamps of Colombia to find out  why coastal ecosystems - mangroves, seagrasses and saltmarshes - are powerful allies in the fight against global warming.