Carbon equivalent
Carbon equivalent (CE) is a metric used to quantify the potential global warming impact of various gases by converting them into a functionally equivalent concentration of carbon. This measurement allows for comparison of the global warming potential (GWP) of different gases over specified timescales, making it a useful tool in climate analysis and reporting. Unlike carbon dioxide equivalent (CO2e), which focuses on the instantaneous radiative forcing, CE reflects time-integrated radiative forcing, offering insights into long-term climate impacts.
CE is particularly significant for international climate agreements, such as the Kyoto and Montreal Protocols, where it helps evaluate emissions and their potential effects. The calculation of CE involves multiplying the mass of a gas by its GWP, with values commonly expressed in billions or millions of metric tons of CO2e. For example, methane has a GWP of 25 over a century, indicating that its emissions have the same warming effect as 25 million metric tons of CO2. Understanding CE is crucial for assessing and mitigating the impacts of greenhouse gases on climate change, providing a framework for both scientific analysis and policy-making.
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Subject Terms
Carbon equivalent
Definition
The carbon equivalent (CE), similar to carbon dioxide equivalent (CO2e), is a metric measure used to quantify how much global warming a given quantity of gas can cause (global warming potential, or GWP), using the functionally equivalent concentration of carbon, converted to the amount of that would have the same GWP as the reference. In contrast to the CE, the CO2e uses the functionally equivalent CO2 concentration as the reference (the amount of CO2 that would have the same GWP). CE is usually given for a specified timescale, effectively expressing the time-integrated radiative forcing. This also differentiates CE from CO2e, which describes the instantaneous radiative forcing.
Significance for Climate Change
The CE of a gas or a mixture of gases is a metric measure that can be used to compare the GWP of for the purposes of analysis, computer modeling, and reporting—as was done, for example, in such international treaties as the Kyoto Protocol and the Montreal Protocol. The CE of a gas is calculated by multiplying the mass (in metric tons) by the GWP of the gas and is expressed for a specified timescale. CE values can be converted to CO2e units simply by multiplying the CO2 by 3/11 (the ratio of the molecular weight of carbon to that of CO2). Time is an important factor when comparing CE or GWP values, as they are functions of the time periods over which these values are calculated.
The United Nations climate change panel, known as the Intergovernmental Panel on Climate Change (IPCC), an intergovernmental organization charged with evaluating the risk of climate change caused by human activity, expresses CE in billions of metric tons of CO2e. In industry, CE units are often expressed in millions of metric tons of CO2e; for vehicles, units are in grams of CO2e per kilometer. For example, the GWP for methane gas over one hundred years is 25; the equivalent value for nitrous oxide is 298. This means that the emission of 1 million metric tons of methane or nitrous oxide has the equivalent ability to contribute to global warming as 25 million or 298 million metric tons of CO2, respectively. Over the same timespan, the hydrofluorocarbons fluoroform (HFC-23) and 1,1,1,2-Tetrafluoroethane (HFC-134a)—shown to have large negative effects on the environment—have GWPs of 14,800 and 1,430, respectively.
"Carbon Equivalents: Your Guide to Accurate Reporting." EcoHedge, 17 Dec. 2023, www.ecohedge.com/blog/carbon-equivalents-your-guide-to-accurate-reporting/. Accessed 13 Dec. 2024.
"CO2-Equivalent Explained." Climate Now, 10 Oct. 2022, climatenow.com/video/co2-equivalent-explained/. Accessed 13 Dec. 2024.
"What Is a Carbon Equivalent (CO2E)?" Arbor, 25 Oct. 2024, www.arbor.eco/blog/what-is-a-co2-equivalent-co2e-carbon-101/. Accessed 13 Dec. 2024.