Carbon Neutral means that producing and burning a carbon based fuel will not increase the carbon dioxide in the atmosphere. This can only be possible if the amount of carbon released into the atmosphere is extracted from the atmosphere.
CO2 in the atmosphere is plant food, and that is a good thing, but nature is very efficient and will often have multiple purposes for a natural process: CO2 in the atmosphere also helps keep the planet warm. Too much of a good thing can lead to a bad thing—Global Warming. Carbon neutral fuels help prevent too much CO2 from accumulating in the atmosphere.
Burning plant biomass, either directly for heat and electricity generation, or as biofuels for transportation, will release carbon into the atmosphere in the form of CO2 emissions, where the carbon can then be used again for new plant growth. When biofuels release carbon into the atmosphere the emissions are considered to be carbon neutral because the carbon is continuously recycled from the atmosphere as new energy crops are grown each season to make more biofuels.
When carbon based fuels are burned, oxygen molecules from the air combine with carbon atoms in the fuel, producing carbon dioxide (CO2) molecules. When the CO2 molecules enter the atmosphere they quickly disperse. In other words, CO2 naturally spreads through the atmosphere, equalizing CO2 concentrations around the globe, similar to how oxygen released by trees and plants in remote locations is shared by the entire planet. CO2 does not form “clouds” of carbon dioxide in the atmosphere hovering over its place of origin. CO2 will spread through the air quickly, so it really doesn’t matter where CO2 is released: Mexico, China, India, Los Angeles, London or Moscow — it doesn’t matter, CO2 produced anywhere, will soon be everywhere.
The carbon atoms released during the combustion of biomass or biofuels will not cause a net increase of carbon in the atmosphere because growing the crops takes carbon out of the atmosphere. In contrast, the carbon released by burning fossil fuels is not part of the natural carbon cycle—because the fossil carbon was taken out of the earth and added to the atmosphere, causing a net increase of atmospheric CO2.
In order for fossil fuel emissions to be carbon neutral, the carbon released from the fossil fuel combustion must either be prevented from entering the atmosphere, as with carbon capture and sequestration (CCS), or taken back out of the atmosphere (extracted). However, if the emissions are allowed to enter the atmosphere, it would not be necessary to extract the carbon out of the atmosphere immediately after it is released from a vehicle, or elsewhere, because achieving a carbon neutral balance averaged over one year would be all that is required. The CO2 emissions would need to be removed from the atmosphere within one year, mimicking nature’s cycle of new biomass growth each season.
And, it would not be necessary to extract the carbon from the same location where the combustion and emissions occurred, because, as described above, CO2 released anywhere on the planet is soon everywhere, therefore, the opposite is also true: removing CO2 from the atmosphere anywhere on the planet will soon reduce CO2 concentrations everywhere.
One ton of pure carbon when burned with pure oxygen will produce 3.67 tons of CO2—one CO2 molecule weighs about 3.67 times more than a single carbon atom. This means that dividing the weight of a given volume of CO2 by 3.67 will give the weight, or amount, of carbon within the given volume. For example, The 2009 U.S. Greenhouse Gas Inventory Report Executive Summary, published by the Federal EPA, says the U.S. Transportation sector releases about 2 billion tons of CO2 into the atmosphere annually: 2 billion tons divided by 3.67 gives 545 million tons of carbon that must be extracted from the atmosphere each year in order to maintain a carbon neutral balance. (The removal of 545 million tons of carbon will reduce atmospheric CO2 by two billion tons.)
Giving allowance for the increasing volume of carbon neutral biofuels, let’s say a rounded figure of 500 million tons of carbon (equal to 1.835 billion tons of CO2) would need to be extracted from the atmosphere over the period of one year by deliberate human (anthropogenic) design; in other words, by technology—in order to make the transportation sector carbon neutral.
500 million tons is a lot of carbon, equal to about half the amount of coal mined in the U.S. every year, but less than 1/10th of annual global anthropogenic carbon emissions* which is about 7 billion tons annually.
(* Carbon emissions and CO2 emissions are not the same thing. Remember, CO2 weighs 3.67 times more than pure carbon—7 billion tons of carbon emissions multiplied by 3.67 explains the 25 billion tons of CO2 emissions often cited by the media. Of course, extracting carbon from the atmosphere will remove the entire CO2 molecule from the atmosphere. The oxygen within the CO2 molecule will be separated and released back into the atmosphere. The pure carbon can then be isolated and buried for centuries; thereby keeping it out of the atmosphere.)
Fortunately, Nature has provided a biological Carbon Sponge capable of absorbing an additional 500 million tons of carbon (equal to 1.835 billion tons of CO2) from the atmosphere, and more, every year. But it isn’t going to happen without human effort—we are going to have to “farm” the carbon out of the atmosphere.
When we think of farms, the first image that comes to mind may be wheat or corn, or perhaps soybeans, potatoes or sugar beets. But not all farms grow food. A Carbon farm would be dedicated to growing biomass for the production of biochar dedicated to the purpose of increasing Soil Carbon — a form of carbon sequestration that not only removes carbon from the atmosphere but also makes possible the conversion of marginal or desert waste land into productive agricultural land; a gift for future generations.
A Carbon farm would not need to use agricultural land or compete for scarce water and fertilizer required for growing food crops. A Carbon farm would do well on marginal land or useless land, requiring only waste water, or seawater.
Microalgae are prolific carbon sponges, an ideal crop for a Carbon farm. Microalgae (pond scum) are among the most prolific photosynthetic organisms on the planet, capable of doubling biomass every 24 hours if optimal growth conditions are maintained, resulting in exponential growth. One acre of shallow water properly maintained can produce 40 tons of microalgae per year (dry weight) having 30-50% carbon content. Ten tons of pure carbon in the form of biochar can be produced from 40 dry weight tons of microalgae.
A microalgae Carbon farm would be different from a microalgae biodiesel farm. There is already a growing international interest in microalgae to produce a bio-oil that can be used to make biodiesel—a substitute for petroleum diesel fuel. Production of bio-oil from algae has yet to fulfill its promise. The algae strains that produce high concentrations of lipids (oil) do not produce well in open ponds or open raceways, because the open ponds are invaded by local species, which are often low-lipid algae strains that dominate the weaker high-lipid algae; causing poor lipid production. High production rates of algae oil are confined to closed systems, which are very expensive.
Carbon farms would not be concerned with the oil content of the biomass. Cheap prolific pond scum, low in lipids and low in proteins will do just fine. A Carbon farm would only be interested in the carbon locked within the biomass molecules. It is the photosynthesis that matters; and pond scum—local species low-lipid algae—are just what is needed, and happen to be the least expensive biomass to produce, in fact, it is very expensive to try to stop an algal bloom. In June of 2008, a giant algal bloom covering 5000 square miles of Chinese coastal waters threatened the Summer Olympic Sailing competition. The official Chinese news agency, Xinhua, reported that the algae bloom covered a third of the coastal waters designated for the Olympic races. It required 1,000 boats and 20,000 people scooping algae out of the Yellow Sea to keep the Olympic Games open.
Biochar can be produced through a process called pyrolysis, which is also used to make charcoal. Any biomass can be prepared for pyrolysis, and microalgae would require special preparation. After removal from the pond, the algae would be air dried or put through a centrifuge designed to reduce the moisture, and then the dry bulk biomass would be sent through a machine to pelletize the biomass before “cooking” the pellets at 500-800 degrees F. without oxygen. The hydrogen and synthesis gas expelled from the cooking chamber are then burned, externally, to provide heat energy for the process, with plenty of gas left over to produce electricity or methanol for resale (in addition to the biochar produced inside the cooking chamber).
A one acre pond can produce 40 tons of algal biomass per year, which can yield a carbon “harvest” of ten tons. The extraction of 500 million tons of carbon per year from the atmosphere would require 50 million acres of algae ponds: 500 million tons divided by 10 tons of biochar per acre, per year = 50 million acres.
Fifty million acres of algae ponds could make all U.S. transportation — cars, trucks, airplanes, etc. — carbon neutral while still using fossil fuels.
After the carbon is extracted from the atmosphere via photosynthesis and reduced to biochar, it must then be buried in the earth in the form of Soil Carbon in order to keep the carbon out of the atmosphere.
The above example shows the potential of algae biochar, but algae is only one possibility for the commercial production of biochar; many other sources of biomass are available for producing biochar, including agricultural waste, as well as forest residue left-behind by the lumber industry after clearing or after forest pruning to prevent fires. Public landfills are another resource; the enormous amount of yard clippings and other organic material sent to landfills could be “harvested” for carbon, rather than allowed to decay and emit methane into the atmosphere.
Duckweed is another fast-growing aquatic plant currently being researched for its biomass potential. Research has demonstrated the potential of duckweed for bioremediation and environmental carbon capture. The US Department of Energy (DOE) has announced that the Joint Genome Institute, through DOE’s national laboratories, will support the genomic sequencing of duckweed as one of its priority projects directed toward new biomass and bioenergy programs.
Switchgrass is not an aquatic plant, but it would be a good candidate for a Carbon crop; it will grow on marginal lands with little fertilizer and is capable of high biomass yields per acre. A carbon farm could specialize in switchgrass biomass, and in a few years, when cellulosic ethanol technology matures, the farm could switch from carbon production to ethanol production, or a combination of both. Designating switchgrass as a carbon crop would encourage farmers to begin large scale switchgrass farming on marginal lands, and not wait for cellulosic ethanol technology to be proven.