Shipping, in the form of cruises, ferries and even the navy, accounts for around 2% of our emissions that contribute to global warming - just a little less than aviation. The diesel powered vessels also worsens air pollution, the biggest environmental threat to health in the UK. At Portsmouth Harbour, they're on a mission to tackle both of those things. On this week's ClimateCast Tom Heap visits Portsmouth Port who are planning to plug in some of its ships at berth and run them on electricity. He speaks to brains behind the Sea Change project to find out what benefits charging ships could offer Portsmouth and how far the shipping industry has to go to become green. Producers: Emma Rae Woodhouse and Gemma WatsonEditor: Wendy Parker