There’s good news and bad news. Biomass can pollute the air when it is burned, though it will not pollute the atmosphere as much as fossil fuels will. The good news: we can plant trees to absorb the carbon dioxide (CO2) released into the atmosphere by the burning process. Carbon dioxide is an atmospheric gas present in many aspects of the environment: in photosynthesis, combustion, fermentation, volcanic outgassing, and respiration. But because CO2 is part of the carbon cycle, it recycles through many natural processes. So let’s look at the carbon cycle….

The Carbon Cycle
All living things contain the chemical element carbon (C). Carbon is the basis on which living organisms survive. To create the energy necessary for life, living organisms extract carbon from various sources on Earth. For example, plants get carbon from the sun through photosynthesis; animals get carbon by eating plants or other animals. Other forms of energy transfer, like fire, also pass carbon from one place to another. For life to continue in relative balance on Earth, carbon must be recycled constantly between the various carbon stores—or “sinks” —that exist in the environment. This recycling of carbon is the carbon cycle.

Because the carbon cycle is a closed system, a fixed amount of carbon exists on Earth, never decreasing or increasing. But it’s important to remember that even though the total quantity of carbon cannot change over time, the amounts stored in various carbon sinks can indeed change, potentially resulting in imbalances with serious consequences for the planet and its inhabitants. The major carbon sinks include the atmosphere, vegetation, soil, oceans, marine life, and geological reservoirs like fossil fuels. How is carbon exchanged between the carbon sinks? Through cyclical activities: the circulating and roiling of the ocean surface, photosynthesis, plant respiration and decay, and fossil fuel burning.

Balance and Imbalance
Scientists believe that prior to the industrial revolution, the natural transfers of carbon between carbon sinks were generally in balance; that is, the carbon sinks did not significantly increase or decrease the amount of carbon they were holding over time. However, that situation has changed with the burning of fossil fuels. How? By burning fossil fuels and emitting carbon to the atmosphere (in the form of CO2), more carbon is now present in the atmosphere than otherwise would be transferred there by non-manmade activities. Most scientists agree that this atmospheric imbalance in the carbon cycle can change life on Earth as we know it.

Greenhouse Gases
Why should we care that burning fossil fuels increases the carbon in the atmosphere? Because carbon dioxide (CO2), methane (CH4), and chlorofluorocarbons (CFCs) in the atmosphere reduce the amount of heat radiated from the Earth’s atmosphere into space; that heat instead stays in Earth’s atmosphere, warming it more and more. These gases or pollutants are called “greenhouse gases” because they make the Earth function like a greenhouse does. Sunlight heats the land and air as if they were inside a greenhouse, and the gases form a reflective barrier like the glass of a greenhouse, preventing built-up heat from escaping and thereby warming the air in the greenhouse—or the atmosphere—to higher temperatures. Are all greenhouse gases the same? No. In fact, methane is considered 30 times more harmful than carbon dioxide within the scope of the greenhouse gas problem.

BIOMASS: Carbon Neutral
All living things are a form of biomass. When plants grow, they absorb carbon from the atmosphere as part of photosynthesis. Because photosynthesis removes carbon from the atmosphere, it’s a form of carbon sequestration. Carbon sinks sequester—or hold—carbon, removing it from another stage in the carbon cycle. So photosynthesis can really help us deal with the greenhouse gas effect by removing CO2 from the atmosphere. However, when a plant dies and decays, it releases its carbon back to the atmosphere in the form of carbon dioxide and methane. It’s all part of the carbon cycle.

The burning of biomass is a sped-up form of decay. So, when biomass is burned as a fuel, whether it’s wood in a power plant or ethanol in cars, it returns carbon to the atmosphere that was previously absorbed via photosynthesis. Otherwise, this same carbon would have been returned to the atmosphere when the plant decayed as part of its natural life cycle. Therefore, when biomass is burned as a fuel, scientists consider it to be a “carbon neutral” event because the same amount of carbon is released to the atmosphere as would have been released via natural decay. What about methane? When biomass is burned efficiently, no methane is released into the atmosphere. When biomass is allowed to decay naturally, methane is released into the atmosphere. Therefore, the complete combustion of biomass for fuel can benefit the environment. As for the timing of carbon dioxide’s release into the environment, it’s released by combustion somewhat sooner into the atmosphere than it would be through the natural decay process. However, the impact of this acceleration of a few years on the environment is not significant in the context of the entire carbon cycle, in which hundreds of years is a more appropriate unit of measurement.

Many companies and individuals are adopting strategies to become “carbon neutral” in their day to day activities. Strategies include buying electricity from renewable sources, using ethanol to fuel cars, purchasing green energy credits, and planting trees.

FOSSIL FUELS: Carbon Positive
Because fossil fuels exist beneath the Earth’s surface, these carbon reservoirs would not otherwise release carbon to the atmosphere naturally as part of the carbon cycle. Therefore, the process of mining these fuels and burning them actually adds carbon to the atmosphere. For this reason, scientists consider the burning of fossil fuels to be a “carbon positive” event because additional greenhouse gases, which contain carbon, are added to the atmosphere.

Becoming Carbon Negative
So, if biomass-fueled power plants are carbon neutral, how can we be carbon negative, to actually benefit the environment? By planting trees! Since trees sequester carbon as part of photosynthesis, planting more trees actually reduces greenhouse gases present in the atmosphere. And another thing—by efficiently burning biomass in the Zilkha Biomass Unit, we eliminate methane emissions from this biomass that otherwise would have hurt the environment.

Each of our power plants burns the equivalent of approximately 8,000 trees per year as fuel. So we are going to plant 8,000 trees annually in North America for each power plant we install…and that is good for the environment!