The market where carbon offsets are bought and sold has been projected to grow and grow, as big companies look to prove they can reach net zero. But where achieving reductions in emissions is impossible or expensive, an alternative is to try and arrange for carbon to be taken out of the atmosphere instead. The markets have thrived on linking buyers of carbon offsets - big firms, and even governments - to development projects in poorer countries, where land and labour for tree planting are cheap.

But can these projects be safely verified and measured? Are local communities being exploited to try and make the maths add up? And can the industry afford to admit when a project is underperforming the expectations according to which carbon credits have been sold?

Investigative reporter Max de Haldevang hears from experts and individuals directly involved in high profile carbon offset projects to find out.

Producer: Robert Nicholson

A Whistledown production for BBC Radio 4