perhaps one of the best technologies at solving the carbon problem is nature itself. i've come to brynau wood in south wales, one the last patches of a once enormous ancient woodland. today, a reforestation project is under way. many countries have committed to planting more trees to soak up co2 but my guide 6wyn says the mix of trees planted is crucial to success. when there is a mixed amount of tree species within a forest, so the more biodiverse we have in terms of what's above the ground, the more biodiverse it is below the ground and the more carbon ends up in the soil, where it's stored for a very, very long time. so does he think nature alone could lead us to carbon neutrality? this is a recent plantation. there's around about 15—20 different tree and shrub species and this