Carbon credit trading has been implemented in a number of countries and regions around the world, with varying degrees of success. Here are a few examples of carbon credit trading in action:

1. European Union Emissions Trading System (EU ETS): The EU ETS is the world’s largest carbon trading system, covering over 11,000 power plants and manufacturing facilities in the European Union. Under the EU ETS, companies are given a certain number of carbon allowances, which represent the maximum amount of carbon dioxide they are allowed to emit. If a company exceeds its allowances, it must purchase additional credits from companies that have reduced their emissions below their allotted limits. The EU ETS has been in operation since 2005, and is considered a key tool in helping the European Union meet its emissions reduction targets.
2. Chicago Climate Exchange (CCX): The CCX was a voluntary carbon trading system that operated in the United States from 2003 to 2010. It was made up of over 400 companies and organizations, including DuPont, IBM, and the City of Chicago. Under the CCX, participating companies agreed to reduce their greenhouse gas emissions and could earn credits for doing so. These credits could then be bought and sold on the CCX, providing a financial incentive for companies to reduce their emissions.
3. Clean Development Mechanism (CDM): The CDM is a carbon credit trading program that is overseen by the United Nations Framework Convention on Climate Change (UNFCCC). It allows developed countries to invest in emission reduction projects in developing countries, and receive credits that can be used to meet their emission reduction targets under the Kyoto Protocol. To date, the CDM has approved over 8,000 emission reduction projects in developing countries, helping to reduce greenhouse gas emissions by over 1.6 billion metric tons.
4. Regional Greenhouse Gas Initiative (RGGI): The RGGI is a cap-and-trade program that covers nine Northeastern and Mid-Atlantic states in the United States. It was launched in 2009 and is designed to reduce greenhouse gas emissions from the power sector. Under the RGGI, power plants are required to purchase credits for each ton of carbon dioxide they emit. The proceeds from the sale of credits are then reinvested in energy efficiency and renewable energy projects, helping to drive the transition to a low-carbon economy.

These are just a few examples of carbon credit trading in action. While each program has its own unique features and challenges, they all demonstrate the potential for carbon credit trading to be an effective tool in reducing greenhouse gas emissions and addressing climate change.