These terms are often used interchangeably in everyday conversations about climate change, but they have different meanings. Understanding the distinction is important when measuring and communicating greenhouse gas emissions.
Hence, it is important to briefly define each of these terms: carbon (C), carbon dioxide (CO₂), carbon dioxide equivalent (CO₂e) and greenhouse gas (GHG).

Greenhouse gases (GHGs) are gases in the atmosphere that trap heat and contribute to the Earth's natural greenhouse effect. Human activities have significantly increased the concentration of several of these gases, driving climate change.
Corporate greenhouse gas accounting typically includes the gases covered by international standards, such as the Greenhouse Gas Protocol. These include:

Carbon dioxide (CO₂) is one specific greenhouse gas. It is released naturally through processes such as respiration and volcanic activity, but human activities—including the burning of fossil fuels, deforestation, and certain industrial processes—have greatly increased atmospheric CO₂ concentrations.
CO₂ is the largest contributor to human-caused climate change because of the enormous quantities emitted and its long atmospheric lifetime. While some greenhouse gases, such as methane, have a much greater warming effect per kilogram, CO₂ accounts for the largest share of global anthropogenic emissions.
For example, it is estimated, in the US, in 2022, that about 80% of GHG emissions from human activities are CO₂. (source: US EPA)
In some studies and databases, CO₂ can be misused to refer to all GHG or to CO₂e emissions, causing confusion.

Not all greenhouse gases have the same impact on global warming. To compare their climate effects using a common unit, emissions are expressed as **carbon dioxide equivalent (CO₂e) .
CO₂e represents the amount of carbon dioxide (CO₂) that would produce the same warming effect as a given quantity of another greenhouse gas over a specified period of time. This comparison is based on each gas's Global Warming Potential (GWP), which measures how much heat a greenhouse gas traps in the atmosphere relative to CO₂ over a defined time horizon (typically 100 years in corporate greenhouse gas reporting).
The illustration below shows how the same amount of different greenhouse gases can have very different climate impacts when expressed as CO₂e. For example, while 1 kg of CO₂ equals 1 kg CO₂e,1 kg of methane (CH₄) ** and 1 kg of nitrous oxide (N₂O) correspond to much higher CO₂e values because they trap significantly more heat per kilogram emitted.
​Global warming potential (GWP) values relative to CO2
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By expressing all greenhouse gases in CO₂e, organizations can combine emissions from different gases into a single, comparable total, making it easier to measure, report, and reduce their overall climate impact.

Scientifically, carbon is the chemical element with the symbol C. It is the building block of many substances, including carbon dioxide (CO₂), methane (CH₄), plants, animals, fossil fuels, and diamonds.
In climate and sustainability discussions, however, the word "carbon" is often used as shorthand for greenhouse gas emissions. For example, people commonly refer to a carbon footprint,carbon emissions, or carbon neutrality, even though these terms usually refer to CO₂e rather than elemental carbon alone.
Because this shorthand can be ambiguous, it is generally preferable to use the more precise terms CO₂,CO₂e, or greenhouse gas emissions whenever possible.