The World Green Exchange trades credits derived from both International and U.S. mandated programs. The goal of these mechanisms is to encourage investment in technologies and practices in order to reduce the amount of greenhouse gas emissions and, in turn, slow or even reverse Global Warming.

European Union Emissions Trading Scheme (EU ETS)
Trading Scheme within the European Union

This program is a mandatory cap and trade system with allowances that are set based on historical performance. The first compliance phase spans from 2005 to 2007, while the second compliance phase continues from 2008 to 2012.

Kyoto Protocol
As a result of concerns over the environment that spawned a series of international summits, the United Nations established the Kyoto Protocol.  It is designed principally to reduce greenhouse gas emissions to their 1990 levels. The following are the main types of credits created by Kyoto:

• Assigned Amount Units (AAUs) – These units are the total amount of greenhouse gas that each Annex B country is allowed to emit during the first commitment period of the Kyoto Protocol.
• Emission Reduction Unit (ERU) – These credits are created from Joint Implementation (JI) projects between two Annex B countries leading to certifiable emissions reductions.
• Certified Emission Reductions (CERs) – These credits are created from Clean Development Mechanism (CDM) projects funded by Annex I investors in developing countries.

US Emission Trading
In the U.S., there are a number of initiatives at the regional, state, and local level aimed at limiting greenhouse gas emissions: 

• SO2 Emission Allowances – These allowances were developed by the EPA as a part of a cap and trade program, and defined as tradable instruments to achieve significant reductions in the emissions of sulfur dioxide (SO2) and nitrogen oxide, both principle causes of Acid Rain. 
• NOx Emission Allowances – These allowances were also created as part of a cap and trade system with the goal of cost-effectively reducing summer ozone levels. The Ozone Transport Commission (OTC) agreed to allow interstate trading of NOx credits over an eleven state region, including the District of Columbia.

Renewable Energy
Today renewable markets are created from Renewable Portfolio Standards (RPS), which mandate the use of renewable generation as a portion of utilities generation.

• Renewable Energy Certificates (RECs) – 20 different states and the District of Columbia have created Renewable Portfolio Standards: minimum levels of power derived from renewable sources. In many of these states, utilities or energy marketers can meet their requirements by purchasing Renewable Energy Certificates (RECs) from producers of renewable power.
• New Jersey Solar Renewable Energy Certificates (NJ SREC) – To spur investment in solar energy generation, New Jersey has mandated minimum solar requirements for their utilities and has created the NJ SREC as a tradable certificate that represents all the clean energy benefits of electricity generated from a solar electric system.