Biochar is an idea thousands of years old but one that seemed to have been (foolishly) lost by many along the way.

Like charcoal, biochar is made by baking wood in the absence of oxygen and then quenched. It can then be ground down and worked into the soil to improve fertility and crop yields. It's believed to have been applied thousands of years ago in the Amazon, to generate the Terra Preta.

The biochar locks in much of the carbon captured by the trees and stabilises it. Tom meets Forester Dave Faulkner and his team at Whittlewood to see the productions process in Northamptonshire.

Meanwhile, Josiah Hunt experimented with the process in Hawaii and now supplies across California. As well as capturing carbon and improving the soils, he says they're removing liability wood to reduce forest fires and are helping to produce green electricity.

Can this ancient process help bring new hope?

Producer Anne-Marie Bullock

Produced in association with the Royal Geographical Society. Special thanks for this episode to Professor Stuart Haszeldine and Dr Ondřej Mašek from the University of Edinburgh and the UK Biochar Research Centre.