An analysis of forest-based projects funded through the sale of carbon credits shows that 10% of them may have a net warming effect on the climate because of the way they alter the Earth's albedo, or how much sunlight is reflected back into space.
The study led by scientists in the Oregon State University College of Forestry also offers recommendations for how to avoid this unintended climate warming by incorporating albedo accounting into carbon crediting protocols. Additionally, the research indicates most projects come with comparatively minimal albedo consequences.
The collaboration, which included scientists at Clark University and The Nature Conservancy, used new, publicly available data to factor in albedo changes when determining the climate impact of afforestation, revegetation and reforestation projects, commonly abbreviated as ARR. Afforestation refers to establishing a forest where there previously wasn't one.
Led by OSU graduate student Lynn Riley and assistant professor Jacob Bukoski, researchers analyzed 172 projects across five continents supported by the Voluntary Carbon Market, a decentralized marketplace through which individuals, businesses and other organizations can purchase carbon credits from forestation projects. Many of these entities, but not all, then use these carbon credits to offset their greenhouse gas emissions.
One carbon credit equals 1 tonne (1,000 kilograms) of carbon dioxide removed from the atmosphere and sequestered in vegetation or soils. The projects in the study are rated to provide nearly 800 million tonnes of carbon dioxide emission reduction over the next century.
"Carbon credits are created via established protocols that aim to ensure each credit corresponds to an actual climate benefit," said Riley, a scientist with the American Forest Foundation. "But so far, those protocols have only accounted for greenhouse gases while largely omitting the non-greenhouse gas factors that also can have a big impact on climate."
One of those is factors is albedo. Forestation sequesters atmospheric carbon dioxide through forest growth, but it also tends to decrease surface albedo, which means more solar energy is retained in the climate system (though when when darker shrubs are reforested to woody savannas, albedo increases and additional solar energy is reflected away).
The bottom line is that if a carbon mitigation project causes changes in albedo, those changes need to be accounted for alongside the carbon mitigation to determine the project's overall climate impact.
"I was encouraged to find that a majority of forest restoration projects have small albedo deductions, indicating that albedo changes are likely negating only a small fraction of the carbon-related climate-cooling benefits," Riley said. "And another portion of projects, most of them in tropical and subtropical regions, have albedo benefits that are unaccounted for, indicating they may be providing even greater climate cooling than they're credited for."
But the scientists also found evidence suggesting 10% of the projects are actually making the climate warmer once albedo changes are taken into account. Despite that, the authors are heartened by what the future holds.
"What's really exciting is that we have independent, accessible data with global coverage to start preventing this today," she said. "It's something that actors across the market - project developers, buyers, ratings agencies, policymakers, etc. - could begin to relatively simply and transparently incorporate into their workflows. That will help climate financing flow to the most impactful projects."
For all 172 projects, the median albedo deduction was 18%; that means that when albedo was factored in, the projects lost a median of 18% of their climate benefit. A quarter of the projects had albedo deductions of 50% or greater, including 12% of the projects for which the entire carbon benefit was negated by changes in albedo. Conversely, the analysis showed 9% of the projects resulted in an albedo benefit, meaning they both scrubbed carbon and made their surroundings more reflective.
"Carbon crediting projects have taken lots of criticism in recent years, but one thing they have done well is evolved with the best available science," Bukoski said. "It's encouraging to see opportunities for more holistic accounting of the climate impacts from forestry projects."
"Albedo and other non-carbon climate benefits like evapotranspiration and snow cover duration could be credited in the carbon market once additional science and accounting have been developed to do so credibly," Riley added. "That could mean more accurate accounting and more funding and resources for the people, projects, and places providing the greatest climate impact."
College of Forestry faculty members Loren Albert and Chris Still also contributed to the study, which was published Oct. 6 in Nature Communications.
"When they are designed with integrity and informed by the best available science, carbon market projects are a powerful and necessary tool for mitigating climate change," said Susan Cook-Patton, lead forest restoration reforestation scientist at The Nature Conservancy. "This study adds to the growing body of science that is helping ensure the voluntary carbon market meets rigorous standards and nature-based solutions to climate change are implemented with precision."
