The emission allowances created under the Kyoto Convention makes its trading possible.
The name is CDM.
Learn about the clean Development Mechanism by reading the article on Wikipedia. Get a feeling about the market of Carbon Credits in the Clean Development Mechanism by reading this article of the Financial Express
You can use the CDM instrument to finance the starting costs of planting trees. By planting eroded areas with the Groasis Technology your capital request is low as your investment in soil is low. Read about economical perspectives in three templates with financial models for reforestation projects in three different continents