representing an allowance to emit one metric tonne of CO2) to nations that exceed their quotas. It is also possible for Annex I countries to sponsor carbon projects that reduce greenhouse gas emissions in other countries. These projects generate tradable carbon credits that can be used by Annex I countries in meeting their caps. The project-based Kyoto Mechanisms are the Clean Development Mechanism (CDM) and Joint Implementation (JI). There are four such international flexible mechanisms, or Kyoto Mechanism, written in the Kyoto Protocol.