The Carbon Trading Wheel of Fortune

Carbon credits are a component of trading schemes implemented to mitigate global warming. They provide a way to reduce greenhouse effect emissions by capping total annual emissions and letting the market assign a monetary value to any shortfall through trading in similar way as the market values stocks of publicly trading companies. Credits can be exchanged between businesses or bought and sold at the prevailing market price. They can be used to finance carbon reduction schemes between trading partners and around the world.

A central authority (usually a government or international body) sets a limit on the amount of a pollutant that can be emitted. Companies are then issued emission permits and are required to hold an equivalent number of allowances (or credits) which represent the right to emit a specific amount. The total amount of allowances  cannot exceed the cap, limiting total emissions to that level. Companies that need to increase their emissions must buy credits from those who pollute less. The transfer of these "credits" is referred to as a trade. In effect, the buyer is paying a charge for polluting, while the seller is being rewarded for having reduced emissions. Thus, in theory, those that can reduce emissions most cheaply will do so, achieving pollution reduction at the lowest possible cost. The concept is that this would give companies, countries, and individuals a financial incentive to produce less CO2 and creating business opportunities along the way:

• 3Degrees sells VERs ( a.k.a. carbon offset, is a reduction of one metric ton of greenhouse gas emissions below a baseline or business-as-usual level.) from carbon reduction projects, providing revenue that helps make projects financially attractive. These VERs offer a low-cost, practical solution to reducing their carbon footprint.
  
  
• BalanceCarbon help businesses understand their impact on the  environment. Some of their services  include Greenhouse Gas Emission Auditing, Energy Efficiency Audits & Advice, Provision of Certified Greenhouse Gas Emission Offsets, etc.
  
  
• CleanAirPass Based on the specifications of your business activity (car/fleet, air travel, event, business, home), they do a custom calculation of the greenhouse gases created and will administrate the purchase of emission offsets on your behalf. A sticker on your windshield or other marketing materials let people know you're part of the program to promote renewable energy and other projects that reduce greenhouse gas emissions.

There's even a Carbon Catalog or directory of Carbon Offset Providers.