What is a Carbon Dioxide Equivalent (CO2e)?

Posted by e.taub@tvcnp.com | Posted in Carbon Footprint, Climate Change, EPA, Greenhouse Gas, Pollution, Science | Posted on 02-04-2010

In order to identify the best actions toward Greenhouse Gas (”GHG”) reduction, we have to look at and account for a lot more than just CO2 emissions. The global warming potential (GWP) of CO2—the most prevalent GHG, but not the most potent—is the base unit by which all other GHGs are measured and is determined by how the GHG molecule absorbs light, as well as how long it lingers in the atmosphere. There are six GHGs with varying GWP.

Though these gases are present in the atmosphere at much lower concentrations than CO2, changes in their atmospheric concentration has a more profound impact than that of CO2 because they cause greater radiative forcing—or change in the amount of radiative energy entering the atmosphere, versus that leaving.
CO2e (expressed in parts-per-million, by volume) is the concentration of CO2 that would cause the same amount of radiative forcing as some concentration of a particular GHG. Looking at the relative effects of other GHGs in the same scale with CO2 provides a basis for including that data in the global warming equation and taking more strategic action to manage the greatest impacts.

Where you look for CO2e is an important component in capturing larger portions of an economy’s footprint, and more efficiently managing reduction of the most significant contributors to global warming. The Waxman Markey bill captures 80+% of US CO2e by focusing on the electricity sector, oil refineries, gas, and large industry (steel, paper, chemicals, etc), while mandatory GHG reporting requirements passed last year allowing the EPA to track large emitters captures 85% of US CO2e.

The EPA is currently looking at tracking additional emissions, including methane, from oil and gas industries. In a press release, Pamela Campos, an attorney with the Environmental Defense Fund stated, “The public has been left in the dark about methane emissions from the oil and gas industry. EPA’s leadership in requiring disclosure of this potent greenhouse gas will mean more rigorous information and smarter policies to address pollution.” New GHG reporting requirements would also be added for industries that emit fluorinated gases or inject and store CO2 underground.

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