The international community is resting much of its hopes on a practice known as carbon trading.
And under the main UN scheme, rich countries are able to offset their emissions by paying for projects in poor countries.
However, the BBC has unearthed disturbing evidence that the system is fundamentally flawed.
In this two-part special investigation, Mark Gregory delves into this multi-billion US-dollar industry and discovers that carbon trading is not working and emissions are not being cut.
If you missed Part One, you can listen to it again below.