Want to solve climate change? Let forests be forests.

Want to solve climate change?  Let forests be forests. That’s the message of a new study released last month by the Nicholas School of the Environment at Duke University and Oregon State University.  

The study comes at a time when biomass energy is in the news a lot. Power companies are facing increasing pressure to find alternatives to burning fossil fuels like coal and one of the easiest fuels for them to swap into their power plants is trees—or what’s known as “woody biomass”.  As a result, the EPA and states like Massachusetts are trying to figure out how to regulate biomass-burning facilities, what limits to place on its use, and how to account for biomass carbon emissions.

The industry promotes biomass power as a way to reduce carbon emissions in the power sector and mitigate climate change. Their argument is simple and hasn’t changed much since they started making it: It goes something like “Trees grow back. Therefore energy produced from burning trees is ‘carbon neutral’”.  

What they’re saying, in other words, is that the carbon emitted when we burn trees for energy is carbon those trees have sucked up out of the atmosphere and will suck up again when a new tree regrows. So carbon in equals carbon out.

But just because trees have the potential to grow back, does that mean it makes sense to burn them in our power plants as a climate mitigation strategy?

Trees are part of an ongoing carbon cycle between the biosphere and the atmosphere. Trees grow, absorbing carbon out of the atmosphere and accumulating it over many decades. Then at some point they die, decay, and release that carbon back to the atmosphere. 

In an ideal world, we could swoop into a forest and grab trees the day after they’ve died and use them to produce electricity. By doing so, we would leave the carbon cycle undisturbed and benefit from capturing that energy to power our homes and businesses. 

But of course it’s impossible to know exactly when a tree has died. So what the biopower industry is actually doing is going into forests and harvesting trees that are alive and well and would otherwise continue growing. By doing so, they arrest the natural carbon cycle and forego all the carbon absorption those trees would provide if left untouched—so the “carbon in” side of the equation takes a big hit.

What happens to carbon emissions going out into the atmosphere?

By substituting in trees, biomass-burning plants avoid fossil carbon emissions. But trees are half water by weight, which means there’s less potential energy per unit of carbon emissions in biomass energy than in fossil fuels like coal. In other words, to get the same amount of energy, you have to burn a lot more trees, emitting about 50% more carbon into the atmosphere per BTU of energy generated. So the “carbon out” side of the equation grows larger.

The result? It’s simple math. Less carbon in and more carbon out means a large “carbon debt” that takes many decades of additional carbon absorption to repay. 

Despite some regional variations in climate and forest type, study after study has confirmed this math for forests around the country. These studies have shown that burning trees in power plants increases emissions relative to fossil fuels for many decades—anywhere from 50 to 100 years or more. 

The findings are powerful. Not only do they discredit the industry’s argument, but they point to the risk of rewarding power companies for burning trees and undermining efforts to invest in truly low-carbon energy sources like wind, solar, and low-carbon biomass—the technologies we need to scale up quickly if we are to transform our energy sector and bring down carbon emissions to levels that avoid the worst consequences of climate change.

With the release of last month’s study, it seems that we are finally getting to the heart of the matter: if mitigating climate change is our goal and we’re looking for ways to use forests in that effort, then we need look no further. Forests are already doing the very best thing they can do to help us in that effort. They are being forests. Giant, super duper effective carbon sucking machines. And any alternative climate mitigation purpose we’d like to put them towards has to be compared to what would happen if we simply let them be. 

Through an incredibly comprehensive analysis across a whopping 1764 combinations of ecosystem properties, initial landscape conditions, harvest frequencies, and bioenergy conversion factors, the study’s authors do a great job of making this straightforward point:

“If a forest is managed for the production of bioenergy to substitute for traditional fossil fuel energy as part of an effort to ameliorate atmospheric CO2 concentrations, such a strategy should be gauged by the climate change mitigation benefits that would accrue by simply leaving the forest unharvested. Ascertaining the point at which a given strategy provides the maximal amount of climate change mitigation benefits requires accounting for the amount of biomass harvested from a forest under a given management regime, the amount of C stored under a given management regime, and the amount of C that would be stored if the forest were to remain unharvested.”

The authors find that regardless of land-use history and ecosystem characteristics, most scenarios required well over 100 years to reach “carbon neutrality”. That means that for at least 100 years, we are better off leaving our forests to grow and do their thing as carbon sinks.

Already in the U.S., we count on our forests to suck up more than 13% of our total, economy-wide greenhouse gas emissions each year. That’s like taking more than 180 million cars off the road. And not only are our forests working hard to pull carbon out of the atmosphere, they’re doing double duty filtering water, giving us open spaces to hunt, fish, and camp with our families, and providing habitat to loads of critters.

So let’s let forests do what they do best while we Americans do what we do best: innovate and deploy new clean energy technologies in energy efficiency, wind, solar, and low-carbon bioenergy that we need to create jobs, bring down our carbon emissions, and create healthier communities. Our forests aren't fuel.