The emission allowances created under the Kyoto Convention makes its trading possible.
The name is CDM.

Learn about CDM by reading the article on Wikipedia about the Clean Development Mechanism
Get a feeling about the market by reading this artikel on the Financial Express

You can use the CDM instrument to finance the starting costs of planting trees. By planting eroded areas with the Groasis waterboxx your capital request is low as the soil costs are low. Read about economical perspectives in the Return on Investment documents