Building China's giant wind farms
8 January 2014 Last updated at 02:28 GMT
More and more cities in China are seeing their streets filled with smog as cars and power stations pollute the air - and one response by the Chinese government is to launch a major push for cleaner renewable energy.
China is now the world's leading producer of wind power and it has plans to install thousands of turbines every year, especially in the remote regions in the country's far west.
Science editor David Shukman went to see of China's giant wind farms taking shape.