Last summer, Science published a controversial study on the potential of planting trees to combat the effects of climate change. The report found that we could increase existing forests—without impacting existing cities or agriculture—by more than 25 percent around the world. The resulting 0.9 billion hectares of new trees could absorb 25 percent of our current carbon dioxide emissions, returning us to levels from nearly a century ago.

These staggering numbers proved to be a bit of an overpromise, as the team later published a correction, acknowledging that forest management is not a silver bullet solution, and noting that suitable land for planting trees will shrink as global temperatures continue to rise.

While the climate crisis undoubtedly requires a more multifaceted approach, scientists agree planting trees remains an affordable and promising strategy for mitigating climate change. However, not every tree planting project is intended to offset carbon. For organizations interested in reducing their carbon footprint through tree planting, it’s helpful to understand the difference between investing in planting trees and investing in verified forestry projects.

How does planting trees remove carbon dioxide?

Carbon dioxide accounts for the largest percentage of greenhouse gases, which contribute to climate change by trapping heat and warming the planet. During photosynthesis, a tree absorbs carbon dioxide from the air, using it to produce carbohydrates as food.‍

All plants remove carbon to some degree. But woody perennials, such as trees, are particularly effective as they can store carbon long-term in the form of cellulose (wood) for hundreds of years. As trees grow, their roots also help store carbon in the soil. According to the USDA Forest Service, American forests and harvested wood currently absorb more than 14 percent of the United States’ carbon emissions every year.

While trees mainly pull carbon from the atmosphere, forests also release carbon dioxide as trees die and decompose. Responsible forest management includes monitoring this natural cycle to enhance carbon capture. 

The difference between tree planting projects and verified forestry carbon offsets 

While all trees absorb carbon, not every tree planting initiative offers carbon offsets, which are credits that companies or individuals can receive to compensate their carbon footprint. Planting trees for carbon sequestration requires an in-depth verification process to ensure the project is contributing to the health of the planet.

Verified forestry projects

Third-party verification services use a standard methodology to evaluate the emissions impact of planting trees, considering aspects such as:

• Additionality. Does the project create a positive impact that wouldn’t occur otherwise? You can’t simply monetize existing forests via carbon offsets.
• Permanence. How long does the impact last? Will the trees be protected from deforestation?
• Leakage. Are there unintended consequences caused by the project, reducing the impact? A project may pay farmers to avoid cutting down a forest for grazing, but if the farmers use the money to cut down another plot of trees, the impact is net zero.
  

Verified tree planting projects typically fall into two major categories: reforestation and afforestation. Reforestation projects restore trees and promote regrowth in existing forests; while afforestation projects plant trees where little to no forest previously existed.

Benefits of Verification

• Measurable impact. Carbon offsets are calculated in metric tons, with each carbon credit equivalent to reducing or removing one ton of carbon emissions. Verification allows companies and individuals to quantify their climate impact, which in turn informs internal sustainability goals, compliance reporting, and more. 
  

• Co-benefits. Responsible forest management comes with co-benefits such as promoting biodiversity by protecting endangered species’ natural habitats, preventing droughts and floods, and creating thousands of jobs. 

Concerns about Verification

• Cost is the main barrier to investing in verified carbon offset tree planting. The verification process can cost over $100,000 and take years, which translates to higher costs for organizations purchasing carbon credits.
  

• Reliability. While verification is currently the most common way to quantify carbon sequestration, it’s not always reliable. Some carbon offset verifiers have recently received criticism for over crediting or mis-crediting projects.    

Non-verified tree planting projects

Non-verified tree planting projects may help mitigate the effects of climate change, but unlike verified reforestation or afforestation projects, they are not designed for carbon sequestration.

For example, Eden Reforestation Projects has planted more than 583 million trees around the world since 2005, employing people to restore and protect forests on a massive scale. Communities suffering from deforestation are often living in extreme poverty, and Eden aims to lift those communities out of poverty through reforestation. Carbon reduction is a potential co-benefit, but it is not the mission.

Benefits of non-verification

• Affordability. A project may decide against pursuing verification for planting trees due to the cost and time barriers, even if they are focused on carbon sequestration. In the absence of verification fees, more of the project’s revenue may be going directly toward tree planting efforts—making non-verified tree planting projects more affordable than verified forestry projects. (Eden, for example, can plant a tree for just 10 cents.) 
  

• Integrated mission. Tree planting projects with a different mission than carbon reduction—such as animal conservation or economic development—often integrate sustainability into their goals. If a company has a lean budget or no need to quantify their carbon footprint within a cap-and-trade system, then a non-verified project may make sense.

Concerns with non-verification

• Unknown impact. Typically, non-verified tree planting projects aren’t able to measure the amount of carbon they remove from the atmosphere. 
  

• Improper management. Without the rigor of verification, improper forest management is possible. While planting a tree seems simple, our ecosystems are delicate. For example, monocultures of fast-growing species popular for tree planting projects, like acacia and eucalyptus, offer few biodiversity benefits and may even harm species-rich forests. 

How many trees have to be planted to impact climate change?

While it’s clear that planting trees does offset carbon dioxide emissions, the potential impact has as much to do with quality as quantity. With a problem as complex as climate change, we need robust solutions—verified or not. No matter which type of tree planting project fits an organization’s needs and interests, it’s important to investigate how it goes beyond “just planting trees” and demonstrates meaningful ecological, economic, and social impact.