February 24, 2020
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Behind carbon-neutral claims: No more carbon besides what’s already circulating

George Danby | BDN
George Danby | BDN

With the new Congress making a priority of advancing the Keystone XL pipeline, issues of the global carbon cycle play prominently in current national debates.

Despite the increased production from North Dakota and Alberta oil fields, the push for technologies to reduce CO2 emissions will undoubtedly continue to pick up steam, especially in the wake of the recent U.S.-China climate accord that long seemed out of reach.

Strong grass-roots efforts will be needed to continue to propel climate issues to prominence on the national and international stage. With that in mind, here’s a look at what some Maine organizations are doing to reduce their carbon footprint by moving toward alternative fuels, along with an explanation of the carbon counting calculus behind their processes.

Tracing a carbon footprint requires piecing together three topics central to the high school science curriculum: photosynthesis, respiration and combustion.

In April 2013, when Colby College became the fourth college or university to attain carbon neutrality, the college’s net CO2 emissions (combustion) did not exceed CO2 withdrawn from the atmosphere (photosynthesis), in large part due to a new heating plant that burns wood rather than oil.

To understand Colby’s claim of carbon neutrality, follow the life of a tree. As it grows to maturity, the tree pulls a certain amount of carbon (in the form of CO2) out of the atmosphere and incorporates it into woody, carbon-based structures (photosynthesis): CO2 plus energy are converted to carbon-based structures.

If that tree were to fall, it could slowly rot on the forest floor (respiration by microorganisms) or be burned (combustion) for heat. Either way the result is the same, releasing from those carbon-based structures stored energy and all the carbon back into the atmosphere as CO2. Respiration (in a living organism) and combustion (not a life function) represent essentially the same process: carbon-based structures are converted to energy and CO2.

The essence of a carbon neutral-claim is that there is no net increase in atmospheric CO2. In any biomass-fired heating system, whether at home in a woodstove or on an institutional scale as in Colby’s heating plant, the CO2 released into the atmosphere as a result of burning wood for heat is the same as the CO2 taken up by the growing tree, so there is no net increase in atmospheric CO2.

Heating by combustion of petroleum, on the other hand, releases carbon (in the form of CO2) into the atmosphere that had long been stored underground (in the form of oil). This carbon, had we not pumped it out of the ground, would not be a part of the contemporary carbon cycle, so it represents a net increase in atmospheric CO2.

Although burning of traditional petroleum heating oil involves an increase in atmospheric CO2, this is not the case for all liquid fuels. For years, the Chewonki Foundation in Wiscasset has been making biodiesel from waste vegetable oil. The carbon-counting calculus is the same as it was for burning wood. The growing vegetable pulls CO2 from the atmosphere and turns it into carbon-based materials, which folks at Chewonki, and many others around the state, convert into fuel. Unlike conventional diesel, when biodiesel burns, it simply returns to the atmosphere CO2 that had already been there recently.

It’s not that these processes don’t emit CO2, for they certainly do. The key is that the CO2 emitted into the atmosphere had already been a part of the contemporary carbon cycle.

Large-scale biodiesel and bioethanol (gasoline additive) production has raised concerns about food security over the use crops of fuel. Additionally, there’s more to the carbon counting calculus, since it requires energy (which usually equates to CO2 emissions) to harvest and process the crops to make biofuels. However, in small-scale facilities, such as Chewonki’s, where the vegetable oil is a waste product from local restaurants — and otherwise destined for disposal — these issues are less of a concern.

Similar to the concerns of large-scale biodiesel production, it is difficult to image how we could sustainably harvest enough wood to convert all current petroleum heating systems in Maine to biomass.

These two examples of biofuels, therefore, represent only a small part of the carbon-neutral solutions needed to fulfill our global energy demands in a sustainable fashion. Solar, wind, and tide will need to continue to grow their share of the energy market so we can wean ourselves from fossil fuels in an effort to reach carbon neutrality.

These examples of Maine organizations leading the charge with biorenewable alternatives to petroleum fuels are only a small part of the grass-roots movement thrusting climate issues into the national and international spotlight.

Reuben Hudson is a postdoctoral fellow in chemistry at Colby College.


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