In the UK, up to 25% of public sector emissions come from the NHS.
To mark the Copenhagen climate change summit, the British Medical Journal has commissioned a short video about how the health service can reduce its carbon footprint.
The video focuses on new born twins Maisie and George and looks at what the world will be like when they reach adulthood.
The film reveals that in caring for patients the NHS uses 18 million tons of carbon every year. The aim is to reduce this to no more than 5 million tons.