Soil is brilliant at capturing carbon dioxide and keeping it out of the atmosphere. But what if we could make it do an even better job? On a farm overlooking the broad River Tay in Perthshire they've sprinkled the fields with the waste product from quarrying. Nature does the rest - using the rockdust to pull carbon dioxide from the air and store it in the soil. With the help of Rachael James from Southampton University, Tom Heap and Tamsin Edwards check out a technique that could be applied to millions of hectares of the world's farmland.

Producer: Alasdair Cross

Made in association with the Royal Geographical Society. Special thanks for this episode to Professor Heather Viles of the University of Oxford, Professor Larissa Naylor and Dr Adrian Bates from the University of Glasgow, and Dr Phil Renforth of Heriot-Watt University.