Desertification is the gradual transformation of arable and habitable land into desert, normally caused by climate change or the destructive use of land. Each year, desertification and drought account for US$42 billion loss in food productivity worldwide.
It is estimated that nearly 20% of China's land area, some 1.74 million square kilometres, is now classified as desert. Affecting the lives of an estimated 400 million people, it is one of the most important environmental issues in China today.
Riding on China's "desertification train", which passes through the country's driest and hardest-hit provinces – Inner Mongolia, Ningxia, Gansu and Xinjiang – Sean Gallagher travelled over 4,000 kilometres to document the environmental challenges along the route.