Not All Bioenergy is Carbon Neutral
Earlier this month the EPA released a policy paper that declared forest biomass a carbon neutral source of energy. Under the right circumstance, that can be true. The trouble is, a blanket policy that treats every burned limb and leaf as carbon neutral — without regard to science — won’t suffice.
Biomass for Energy
Biomass — trees, woody shrubs and annual crops — can be used to produce fuels for many different purposes, including pellets for home heating, liquid transportation biofuels and electric power generation. Converting biomass to energy can be good for the environment but conversion strategies that are too aggressive can also do great damage to our climate and to nature.
A forest land owner who sells the residue from his sawtimber harvests can gain additional revenue that helps pay his property taxes so he can keep his lands in forests. A conservation organization like The Nature Conservancy that markets the small trees it thins from forests to reduce hazardous fuel loads can afford to do even more projects in forests at risk of catastrophic wildfires. Farmers managing lands in developing countries who plant and harvest perennial crops for energy help restore lands that are underutilized or have been degraded by overuse. Higher prices for pulp wood and forest residues may even increase the land area dedicated to forests. Properly managed, these actions can be good for our climate system and other environmental values.
Aggressive Conversion Strategies Pose Risk
But not all uses of biomass to produce energy are beneficial; not all bioenergy is carbon neutral. If a large forest area is clear-cut in the United States and converted to second home development, the result is not carbon neutral. If large areas of the Amazon forest in Brazil are cleared and converted to soybean production or cattle grazing, the result is not carbon neutral. If the tropical forests of South Asia growing on peatlands are burned away to make room for palm oil plantations to supply biofuels markets, the result is a climate catastrophe. Contrary to a new policy announced by the Administrator of EPA this week, no use of biomass to make energy should be assumed carbon neutral; every use must be carefully assessed.
We have made the bioenergy mistake before. In the late 19thcentury, large areas of land in Europe and the United States were cleared for energy use — firewood and crops that provided fodder for draft animals. We understand that our use of fossil fuels today is not sustainable because it adds 5 billion tons of carbon dioxide to the atmosphere each year. Surprisingly, carbon dioxide emissions in the United States from biomass combustion and land clearing were almost 4 billion tons per year in 1900.
We are still recovering from those harvests. Each year, American forests naturally get bigger, taking 800 million tons of carbon dioxide out of the atmosphere and storing it in trees. That offsets more than 10 percent of our fossil fuel emissions. This has been going on year after year since the 1930s. The eastern U.S. forest is now 60 percent restored. Bioenergy policies should not interrupt this restoration.
The U.S. is home to many different types of forests each supporting unique communities of wildlife. Some original forest stands — such as long-leaf pine — have been greatly depleted. When Europeans came to America, the long-leaf pine forest covered 90 million acres; it is down to less than 7 million acres today. Although the remaining long-leaf pines could be replaced with some fast-growing plantation tree to support bioenergy markets, no person who loves our natural heritage would salute that outcome — even if it is carbon neutral.
Biomass Is a Goldilocks Fuel
Bioenergy requires tremendous land areas for the energy it provides. It is not an efficient way to convert sunlight into power. Producing biofuels from soybeans may require a land area 1000 times greater than the land needed to produce the same amount of energy in diesel fuels from wells that yield petroleum. Producing power from solar or wind energy sources need one hundredth of the land area to produce the same kWh of power from burning forest materials. On the other hand, using certain biomass resources such as mill residues, harvest slash and small trees from ecosystem restoration projects may support environmental benefits that wind and solar energy cannot provide.
So, biomass is a Goldilocks fuel. You can try to do too much with biomass and harm our climate system. But you can also do too little and lose forests and grasslands to urban and second home development, cattle grazing and palm oil plantations. Defining a thoughtful middle ground that uses bioenergy markets to support the nature benefits of forests and grasslands, provides revenues to landowners and secures climate benefits requires needle threading that has so far eluded our federal environment, agriculture and land management agencies. The EPA’s new policy recognizes the value of avoiding the conversion of forested lands to non-forest use, but achieving real carbon benefit requires that science be applied to measure carbon emissions from planting to harvest to conversion at each bioenergy facility. A blanket policy that all bioenergy is carbon neutral won’t suffice.
Beyond the environmental considerations, many types of bioenergy face cost challenges. Today, biomass energy is generally more expensive than other types of primary energy that we rely upon to produce electric power, home heating and transportation fuels. There would be no significant market for bioenergy without it being advantaged through government policy — subsidies or mandates — to put it ahead of natural gas, wind and solar power in the marketplace. If we are concerned about the potential negative impacts of bioenergy systems on climate or wildlife habitat, we must keep a close watch on government policy.
One day soon, government policy will put a price on the carbon emissions from the fuels we use providing incentives for energy efficiency and low carbon sources of power. Some pathways to bioenergy based on residuals from harvests or mills, very high-yielding energy crops on previously cleared lands, or material from forest thinning to reduce risks of catastrophic fires will be able to compete in a market with a carbon price because they are truly low carbon — and can be proved to be so with good science. What we should fear is a policy that treats every limb and leaf that is burned as carbon neutral without regard to science. The force of such a declaration, embedded in a carbon tax, would return us to the devastation of the late 19thcentury when our forests were depleted more rapidly than they could regrow.
Bioenergy is not carbon neutral. But it is an opportunity to make modest gains for our climate and for our forest and grassland ecosystems, if we have the wisdom to be modest in the expectations that we claim for it.
Originally published at blog.nature.org on April 30, 2018.