The climate tipping points

The melting of polar ice sheets, the collapse of the Amazon rainforest, the seizing up of ocean circulation - these are just some of the calamities we risk bringing about through our unabated carbon emissions. Each of these tipping points on its own could have dire consequences for the wellbeing of all life on Earth, including us humans. Justin Rowlatt discovers how global warming may trigger irreversible changes to our planet.