Emissions: What's the difference?
Today I recieved a great question from a colleague about the different terminology that climate people use when talking about emissions. She asked: "What's the difference between carbon emissions and greenhouse gas emissions? It seems like they're used interchangeably, but what are the nuances to each?"
This is a great, foundational terminology question - especially if you are trying to make sense of the many emissions reduction efforts out there right now. Sometimes the two names are used interchangeably, but they’re not the same thing! These groups of emissions differ in three key areas:
| Carbon emissions | Greenhouse gas (GHG) emissions |
Difference #1: What kind of emissions are we referring to? | Carbon emissions refers to carbon dioxide emissions. CO2 is the most abundant warming gas in our atmosphere, so is often targeted by emissions reduction programs. When people talk about “reducing emissions” they sometimes conflate all emissions and CO2 as being the same thing. | GHG emissions refers to all of the warming gases in our atmosphere, including CO2, methane, nitrous oxide, and other gases. Each of these gases has a different ‘lifespan’ in the atmosphere and each differ in how effective they are at trapping heat in our greenhouse atmosphere. For example, methane only makes up about 16% of GHG and has a shorter lifespan, but it is much better at trapping heat. Because of this, the IPCC estimates that the comparative impact of methane is 25 times greater than CO2 over a 100-year period! |
Difference #2: What are their sources? | CO2 emissions are generated primarily by the transportation sector, by electricity generation, and by industrial production like steel, cement, and chemicals. | GHG emissions come from a variety of sources – not just CO2 emissions sources as described at left. As a result, abatement measures are a lot broader. |
Difference #3: What measures can we take to reduce them? | Given its sources, to reduce carbon emissions we might look at electrifying personal/municipal vehicles and trucking fleets, converting electricity grids to renewable sources, and strongly regulating the environmental impacts of industrial production. | Abatement measures are different depending on the gas being targeted, and so a spectrum of solutions could be employed. For example, methane is produced by agriculture and by fossil fuel extraction, so we might look at capping methane leaks or reducing livestock emissions. These are different from the CO2 abatement efforts described at left. |
Why does this matter? As a consumer, you can use this information to evaluate the climate commitments of your favorite companies. As a voter, you can better understand and question the efficacy of policies being proposed by your elected officials. For example - politicians have lately been talking about addressing methane emissions. Capping methane leaks is relatively low effort and will have a big impact in reducing global warming!
Want to learn more?
The United Nations published this piece on methane emissions ahead of the announcement of the Global Methane Pledge at last fall’s global climate summit, COP26
The EPA has a detailed breakdown of the sources and abatement tactics for different GHGs (though it is US-centric, so bear in mind)
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