Ask TreeHugger: What Does "Carbon Neutral" Mean Anyway?

A fire pit burning wood in a setting with bushes and grass.

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Question: I fail to understand how these logs could be considered carbon neutral. Are you saying that the material they are made of has absorbed carbon over its growth life and is now releasing it, so that carbon is neutral? What about the extra carbon that those plants and trees contain, that are not absorbed, but rather created by their growth. When burned, I think they put out more carbon than they absorbed during their life.

Response: For this case, "carbon neutral" simply means that no extra carbon dioxide is released into the atmosphere when the plant waxes in the logs are burned. [Note that a different definition of "carbon neutral" describes carbon off-setting and means that any carbon emitted into the air is offset by tree planting or new conservation measures to lower the amount of emitted carbon dioxide. The term "carbon neutral" has come to prominence because of concerns about carbon dioxide's role in global warming. Carbon dioxide is a greenhouse gas, meaning that it can absorb infrared light, which allows it to trap energy from the sun and warm the earth. Although it is currently seen by the public as a "bad" actor, it is important to remember that carbon dioxide is also essential to life. Plants take in carbon dioxide and convert this carbon dioxide into energy in the form of a variety of carbon-based substances, including glucose, proteins, starches, and oils that the plant needs to survive. People, on the other hand, exhale carbon dioxide, as a natural byproduct of breathing.

The problems posed by carbon dioxide do not reflect these natural processes, but rather human activities, of which the most notable are fossil fuel burning and deforestation. These and other human activities add over 30 billion tons of carbon dioxide each year into the atmosphere, with the greatest contribution from fossil fuel burning. Fossil fuel burning is "carbon positive", in that it moves carbon stored deep in the earth (in the form of coal, natural gas, or petroleum) into the air, where it contributes to global warming.

Unlike fossil fuels, when biofuels and other plant-based substances are burned, no extra carbon is added to the air, even though this process also releases carbon dioxide into the air. Why is this? In brief, it is because the plants store carbon only for short periods of time (meaning for months and years, rather than millions of years as with fossil fuels). As a result, when plant-based substances are burned, the carbon dioxide is essentially recycled, moving from air to the plant back to the air. Although this recycling takes some time, the amount of time it takes is much shorter than the amount of time global warming effects take. In other words, the basic idea is that the carbon removed from the air by the plants cancels out the carbon emitted by the plant when it is burned.

Of course, all of this ignores the fact that fossil fuels were burned to make and transport the burning logs, thus adding extra carbon dioxide into the air. For example, electricity was used to make the logs, while gasoline or diesel fuels were burned to transport the logs from the plant to stores. As a result, burning these plant-based manufactured logs cannot truly be "carbon neutral".

Helen Suh MacIntosh is a professor in environmental health at Harvard University and studies how pollution behaves in the environment and how it affects people's health. Please keep in mind that her answers are just her interpretation of available information and should not be taken as the only viewpoint or solution to a problem. Use this column at your own risk. Having said this, please feel free to post any of your environmental health questions to (Please use a descriptive email subject line and mention if you want to remain anonymous or not).