Tree Planting Efforts Could Actually Worsen Climate Change

Scientific American

06-06-2025

CLIMATEWIRE | Carbon markets that fund forest preservation and tree-planting might actually be worsening climate change by increasing risks for wildfires that emit massive levels of greenhouse gases, a new United Nations-affiliated report says.
Forests have been seen as one of the most effective places to counter climate change by absorbing carbon emissions. But that's changed, says a May paper from the United Nations University Institute for Water, Environment and Health (UNU-INWEH), an academic arm of the international U.N.
In the past decade, wildfires of record-breaking size have erupted in places such as Canada, Australia, Siberia and the Amazon rainforest. This week, forest wildfires forced evacuations of thousands of Canadians in Manitoba and Alberta provinces.
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'Forests and peatlands have increasingly transitioned into massive carbon emitters in many parts of the world due to increasing wildfires,' the report says. Climate policies and carbon-mitigation activities 'fail to account for these substantial emissions.'
The report highlights weaknesses in a central global strategy for addressing climate change — planting and protecting trees — which has attracted billions of dollars from polluters that fund the projects to offset their own carbon emissions. A large share of the money is paid through the voluntary carbon market, a largely unregulated system that has come under increasing scrutiny over its integrity.
Recent major wildfires have been particularly harmful. The 2023 forest wildfires in Canada emitted more greenhouse gases than the total industrial emissions of any country in the world except for China and India, Ju Hyoung Lee, a research fellow at UNU and lead author of the report, said in an interview from Seoul, South Korea.
In California, wildfires in 2024 destroyed parts of forests that were supposed to be storing carbon through an offset program under the state's cap-and-trade carbon market.
Without systematic monitoring of forest conditions, the paper says, the voluntary carbon market and other policies that promote forests 'may unintentionally exacerbate wildfire hazards.'
Planting new trees to absorb carbon could have the opposite effect, the report says, as more heat and increased carbon dioxide emissions from climate change accelerate forest growth while also depleting soil moisture.
'Planting more and more trees in such an environment with the purpose of carbon mitigation will likely increase carbon emissions due to future fires,' the report warns.
When the businesses certifying forest projects in the voluntary carbon market consider wildfire risk, they normally look at historical incidents of fires, Lee said. But, she added, 'Forests are changing, and our forests [won't] be like what it was like for the last 20 years."
Historical data often leaves out the past five years, which includes some of the worst fires on record, Lee said.
As a result, fire risk is typically underestimated by nonprofits such as Verra, which sets standards for and certifies climate projects to be listed on the voluntary market, Lee said. Representatives for Verra did not respond to a request for comment.
Concerns about forests and their changing dynamics have existed for more than a decade, Kaveh Madani, director of the UNU-INWEH, said in an interview from Toronto.
The report hopes to get the message out, Madani said, that existing forest programs and certification standards were developed using science that's now outdated — and the projects 'can increase the risk of increased emissions, in some cases.'
Madani emphasized that not all forest programs in the voluntary carbon market and elsewhere create a wildfire threat.
The paper advocates reforming the voluntary carbon market and similar systems to better account for forest conditions and to prevent unintended consequences, including more wildfires.
Rainfall, soil health, and expected future droughts and heat waves should be considered before approving forest projects 'as a carbon emissions reduction solution,' the paper says.
Satellite observations could identify areas where forests are growing and fuels are accumulating, leading them to be excluded from carbon markets 'due to the potential high emissions in case of future fires,' the paper says.
The risk of wildfire and other environmental conditions that could damage forests 'must be included in our planning for the future and the schemes that we have in place,' Madani said.