What is a Carbon Offset?

Photo of trees on Duke's East Campus

Carbon offsets are reductions in greenhouse gas emissions to the atmosphere. Offsets can be generated in many ways: by planting trees that absorb carbon dioxide (CO2) from the atmosphere as they grow, by capturing and burning the methane (CH4) produced by landfills or farms before it enters the atmosphere, and by improving energy efficiency to reduce energy use and lower associated CO2 emissions. For these emissions reduction projects to generate carbon offsets they must meet a series of requirements, including: internal monitoring, external verification, and a system of accountability, should the project fail to accomplish its climate impact goal.

How is a carbon offset measured?

Carbon offsets are measured in metric tonnes reduced resulting from a project’s impact. The commonly used unit for measuring a carbon offset project’s impact is CO2e, the CO2 ‘equivalent’ impact of a project. Greenhouse gases differ in terms of their ability to increase global temperature and are equated similar to currency exchange rates, to the most common greenhouse gas CO2. For example, one tonne of Nitrous Oxide (NOx) is equivalent to 295 tonnes of CO2 and one tonne of methane (CH4) is equivalent to 25 tonnes of CO2.

What does it mean to ‘Buy an Offset’?

1. Buying a carbon offset means that you gain ownership of one metric tonne of CO2e removed from the atmosphere or prevented from entering the atmosphere by a specific project.

2. When you ‘buy an offset’ you are buying one metric tonne of CO2 reduced from a specific project that caused the reduction in atmospheric greenhouse gas levels.

The commodity you are buying is not a physical good – rather it is a virtual good – like an online currency. While virtual goods do not exist in your hands, you have the exclusive right to trade that currency, and count that offset against your personal or your organizational emissions. Each, one-tonne of CO2e, offset is tracked by a unique serial number, which maintains a link to the project that generated the offsets and allows it to be individually bought and sold. We encourage you to use our carbon calculator to estimate your individual carbon footprint and buy carbon offsets to fight climate change today!

What is an offset ‘Co-Benefit’?

Offset co-benefits are any project benefits other than the primary goal of a carbon offset project, which is to impact the atmosphere’s greenhouse gases levels. Common co-benefits include financial savings, job creation, improved air quality, increased animal habitat and recreation space, reduced health risks, reduced odor (from animal farms), reduced risk of water contamination, the creation of educational value, and much more. Please download a copy of the DCOI's co-benefits guide to learn more.