Optical dating reveals that the height of Earth’s tallest megadunes in the Badain Jaran Desert of NW China is increasing

•Height of Earth’s tallest megadunes in the Badain Jaran Desert is increasing.•Base of the megadune windward slope is eroding and the top is accumulating.•On the windward slope the modern eolian sand layer thickens from the base upwards.•Increased humidity and reduced wind speed favor the growth of megadunes.