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CO2 vs. CO2e: What is the difference and why does it matter?

Understanding the differences between CO2 and CO2e can help businesses more accurately understand the emissions they generate.

Anyone who is confused about the concept of carbon dioxide equivalent is in good company.

As business and IT teams begin their journey to sustainability, they'll encounter a number of new terms. Two common terms are carbon dioxide (CO2) and carbon dioxide equivalent (CO2e). Both measure global warming potential, but the latter includes greenhouse gases besides CO2. For that reason, a number of climate experts recommend using CO2e since it's a more accurate measurement.

What are greenhouse gases?

To understand the difference between carbon dioxide and carbon dioxide equivalent, it's important to first understand what greenhouse gases are and why they matter.

In the simplest terms: Greenhouse gases are those that magnify sunlight and trap heat in the earth's atmosphere. Greenhouse gases from human activities are the main driver of climate change, according to the International Panel for Climate Change and other climate scientists and bodies, including the United States Environmental Protection Agency.

"From 1990 to 2019, the total warming effect from greenhouse gases added by humans to the Earth's atmosphere increased by 45 percent," according to the EPA.

Carbon dioxide on its own increased the warming effect by 36%, according to the EPA.

Greenhouse gases are heating up the earth and causing rising sea levels, and more flooding, hurricanes, fires and droughts, to name just a few problems. These problems, in turn, are also creating issues for companies and their IT teams, including putting business continuity at risk, creating supply chain disruptions and challenging leaders to think of sustainability, perhaps for the first time.

CO2 vs. CO2e: Why the differences matter

Modern lifestyles -- with their reliance on production and consumption of fossil fuels -- produce the excesses of carbon dioxide and other greenhouse gases that drive climate change. Each greenhouse gas has particular sources and effects.

Carbon dioxide is released when people use oil, gas and other petroleum-based fuels -- including for IT and supply chains -- and when people cut down or burn forests.

In 2021, carbon dioxide (CO2) made up about 80% of all human-caused greenhouse gas emissions, according to the EPA.

Moreover, CO2 has contributed more to climate change than anything else between 1750 and 2011, according to the Union of Concerned Scientists, a science-based nonprofit organization.

But CO2 isn't the only greenhouse gas that's driving climate change.

Other greenhouse gases -- such as methane, nitrous oxide and fluorinated gases -- also have powerfully harmful effects on the environment.

Methane, in particular, is coming under scrutiny since it traps more heat per molecule than carbon dioxide.

Methane emissions account for about 15% of global greenhouse gas emissions, according to the EPA. That's largely from animal agriculture. For example, every year, 1.5 billion cattle raised for meat emit at least 231 billion pounds of methane into the atmosphere.

As for the rest of the greenhouse gas emissions: Ozone, water vapor, nitrous oxides and fluorinated gases such as hydrofluorocarbons and chlorofluorocarbons comprise the remaining 5% of greenhouse gases.

CO2e and global warming potential

To understand CO2e requires first understanding the concept of global warming potential, or GWP.

Each greenhouse gas has its own warming potential. This is dependent on two factors: how efficiently it traps heat and how long that greenhouse gas stays in the atmosphere.

The principle of global warming potential, or GWP, is a measure of how long a greenhouse gas will stay active in the atmosphere over a given time, in comparison to the emissions of 1 ton of CO2. The time horizon is typically 100 years. CO2e uses CO2 as a benchmark of 1.

So for example, carbon dioxide scores 1 (as a benchmark), methane would have a score of 25, nitrous oxide would have a score of 298 and some gases would score exponentially higher.

This gives organizations a way to quantify the variety of emissions they produce into a single number.

As the urgency of global warming intensifies, more focus is on the nearer-term, both in terms of effects and action.

CO2e to understand carbon footprint

As more companies focus on environmental, social and governance (ESG) goals in response to government regulations and consumer demand, they are also beginning to focus on understanding their carbon footprint.

The carbon footprint measures the total amount of greenhouse gases a company or person generates, and that requires knowing the CO2e -- and not just the CO2.

Several calculators exist, including a simple-to-use carbon footprint calculator from the EPA.

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