Away from the Wall, they found that vegetation cover and dust storms rise and fall based on the amount of precipitation. But closer to the trees, vegetation increased and dust storms diminished between 1981 and 1998. And Tan says the region continues to improve. "In most places in the study area, greenness continued to increase between 2000 and 2010," he said. "In North China as a whole, we think the environment is getting well."

The insatiable Gobi has been responsible for devouring 1,400 square miles of grassland each year. And each year, dust storms take off as much as 800 square miles of topsoil, and as a result the storms have increased in severity each year.

The fourth and most recent phase of the Great Green Wall was started in 2003 and included aerial seeding to cover large areas of land where the soil is less arid, and offering cash incentives to farmers who plant trees and shrubs in drier areas.

The Wall is intended to have a belt with sand-tolerant vegetation arranged in checkerboard patterns in order to stabilize the sand dunes. A gravel platform will be next to the vegetation to hold down sand and encourage a soil crust to form. The trees also intended to provide a windbreak from dust storms.