In the 21st century air pollution is a major cause of death, according to the World Health Organization (WHO), in 2012 around 7 million people died – one in eight of total global deaths – as a result of exposure to air pollution. This confirmed that air pollution is the world’s largest single environmental health risk. The new estimate is based on increasing knowledge of air pollution-related diseases and use of improved air quality measurements and technology. According to WHO, outdoor air pollution caused 3.7 million premature deaths in 2012. Indoor air pollution is responsible for about 4.3 million premature deaths every year. South-East Asia and Western Pacific Region had the largest number of air pollution-related deaths in 2012, and in these two regions alone, a total of 3.3 million deaths were linked to indoor air pollution and additional 2.6 million deaths were related to outdoor air pollution. The 2014 UNEP Year Book noted that in 2010 the cost of air pollution to society was estimated at US$1.4 trillion in China and an additional US$0.5 trillion in India.
Extreme air pollution also has other effects, in 2014 He Dongxian, an associate professor at China Agricultural University’s College of Water Resources and Civil Engineering, was reported as saying that new research suggested that if the smog persists, Chinese agriculture will suffer conditions “somewhat similar to a nuclear winter”, slowing photosynthesis in plants, which could affect the growth of food crops.
 “7 million premature deaths annually linked to air pollution”, World Health Organization (WHO), Geneva, Press Release 25 March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/ accessed 12 October 2015
 United Nations Environment Programme (UNEP) Year Book 2014, Nairobi, Kenya, p. 43, the cost estimates were taken from a OECD study.
 Kaiman, Jonathan – “China’s toxic air pollution resembles nuclear winter, say scientists”, The Guardian, 25 February 2014