Ertel was soon a big producer at Natsource, trading sulfur dioxide, nitrogen oxide, carbon and even weather derivatives.

FORBES: Selling the Blue Sky

The middlemen are niche investment banks, such as Climate Change Capital and Natsource, and project-management companies, such as Camco and AgCert.

ECONOMIST: Selling hot air

Four billion dollars has been invested in carbon-trading hedge funds like Natsource of New York City and Climate Change Capital in London.

FORBES: Magazine Article