Dense evergreen plantations in Canada's boreal forest absorb so much winter sunlight that the resulting surface warming can offset 6 to 20 percent of the climate benefit they are credited with. Canada's current carbon accounting frameworks measure the carbon stored but largely omit the heat absorbed by these forests, according to a new Policy Brief from the United Nations University Institute for Water, Environment and Health (UNU-INWEH). The result is inflated mitigation estimates and public investment in forests that may not deliver the cooling they promise.
The Policy Brief " From Carbon Accounting to Net Cooling: Securing the Albedo-Carbon Double Win in Canada's Boreal Forest" argues that Canada should judge reforestation by its net effect on temperature rather than by tonnes of carbon stored. "Canada has an opportunity here that few countries have," said Professor Kaveh Madani , Director of UNU-INWEH. "It can be the first to verify forests on what they actually do to the climate, not on what they store on paper. That protects public money, and it protects the credibility of every credit this country issues. Climate leadership isn't about planting more trees anymore. It's about being able to show, decades from now, that the forest we planted is still cooling the ground it stands on."
In snow-covered landscapes, the color of the land surface matters as much as what grows on it. Open snow reflects most of the sunlight that reaches it, but a dark spruce canopy absorbs it. A dense evergreen stand across a snowy landscape makes the ground measurably darker for months of the year, warming the surface even as the trees pull carbon from the air. Scientists call this reflectivity albedo, and most carbon accounting frameworks in use today do not subtract it.
The authors from UNU-INWEH , the University of Waterloo, and Polytechnique Montréal, find that offset frameworks counting stored carbon without deducting surface warming or adjusting for permanence risk systematically overstate reforestation's true climate value. Evidence from the Taiga Plains shows that heat absorbed by dark spruce forests can offset 6-20 percent of their reported carbon gain. Afforestation and reforestation sit at the center of Canada's climate commitments, which makes the gap expensive. The publication treats the exposure as fiscal as it is environmental. Public money may be flowing into forests that absorb more heat and carry elevated fire reversal risk. Without reform, the authors warn, Canada risks issuing low-integrity carbon credits. They call this a policy failure to measure net temperature impact, not a gap in the science.
"A forest can pass a carbon audit and still leave the surface warmer than it was. That's the part nobody is measuring," said Professor Pooneh Maghoul , Lead for Sustainable Infrastructure in Cold Regions at UNU-INWEH. "We're not questioning whether trees help. We're saying the ledger is incomplete, and in the North the missing entry is large enough to change the answer."
Long-term modeling studies in northern Canada show that forest design decides the outcome. Mixed stands with 25 to 40 percent deciduous trees, planted at moderate densities of 600 to 1,400 trees per hectare, hold substantial carbon while reflecting more winter sunlight. They also burn less intensely. Dense evergreen mono-plantations do the reverse, intensifying competition for soil moisture and building the continuous fuel that drives high-severity fire in dry years. Wildfire, the Policy Brief argues, has become the primary constraint on carbon durability in a warming boreal system. In drought-prone country, a dense plantation is a fire liability rather than a climate asset.
"The question isn't how many trees we plant. It's what we plant, how densely, and whether the site can still hold water in thirty years," said Professor Maghoul. "Get that wrong and you've spent public money on something that burns."
The authors urge Canada to establish a Net Cooling Standard that deducts the Albedo Penalty and screens for wildfire permanence across all publicly supported reforestation. They also recommend confining restoration to hydrologically viable under-stocked land, and building a satellite-supported national platform to monitor soil moisture, fuel accumulation and surface reflectivity as conditions change.
Key Findings at a Glance
Heat absorbed by dark spruce forests can offset 6 to 20 percent of their reported carbon gains, based on evidence from the Taiga Plains.
Mixed forests with 25 to 40 percent deciduous trees, planted at 600 to 1,400 trees per hectare, deliver stronger and more durable climate cooling than dense evergreen monocultures.
A mixed stand of approximately 25 percent aspen generates stronger and more durable cooling than conifer-only stands by combining rapid early growth with sustained carbon retention.
In a warming boreal system, wildfire is the primary constraint on carbon durability, not growth rate or planting volume.
Partial harvesting followed by prompt mixed-species replanting maintains stronger and more stable climate returns than full clearcut cycles.
Publication Details
Ofosu, E., Dsouza, K. B., Amaogu, D. C., Pigeon, J., Boudreault, R., Shokri, N., Moreno-Cruz, J., Matin, M., Madani, K., Maghoul, P., and Leonenko, Y. (2026). From Carbon Accounting to Net Cooling: Securing the Albedo-Carbon Double Win in Canada's Boreal Forest. United Nations University Institute for Water, Environment and Health (UNU-INWEH), Richmond Hill, Ontario, Canada. doi: 10.53328/INR26RPM001
