Published papers and research outputs from the Canopy PACT research group and their collaborators.
Unobserved confounders cannot explain over-crediting in avoided deforestation carbon projects
Nature Ecology & Evolution
Alejandro Guizar-Coutiño, George Nicholson, David Coomes, Paul J. Ferraro, Tom Swinfield, Julia P. G. Jones
May 2026
In ecology and conservation, a growing number of studies seek to draw causal inference using quasi-experimental designs. Despite the risk of omitted variable bias from such designs, the degree to which results are sensitive to unobserved confounders is seldom assessed. Here, to demonstrate the value of such sensitivity analyses, we use the controversy surrounding whether projects aimed at reducing emissions from deforestation and forest degradation (REDD+) overestimated their effectiveness (resulting in too many credits being sold). Verifiers of REDD+ credits have argued that independent quasi-experimental analyses of REDD+ projects are flawed because they omit site-specific drivers of deforestation. If these drivers also affect where REDD+ projects are established (that is, projects target areas facing threat), omitting them will tend to underestimate the deforestation that projects avoided. We revisit a global sample of 44 REDD+ projects and show that while some projects reduced deforestation, over-crediting was rife. Crucially, we explore the sensitivity of these results to unobserved confounders and demonstrate that unobserved local drivers of both deforestation and REDD+ locations are unlikely to fully account for reported over-crediting. Assessing sensitivity to unobserved confounders remains uncommon in ecology and conservation but should become standard practice where causal conclusions are based on controlling for confounders.
Permanence Risks to Biodiversity and Nature-Based Carbon Offsets
Conservation Letters
Alexander Dhond, Sophus O.S.E. zu Ermgassen, Thomas Swinfield, Morgan Robertson, Andreas Heinemeyer, Stewart Owen, Joseph William Bull
April 2026
Biodiversity and nature-based carbon offsets are central to strategies addressing biodiversity loss and climate change. Their credibility depends on permanence—the expectation that biodiversity gains or sequestered carbon persist at least as long as the impacts they compensate for, or in perpetuity. Yet ecosystems are dynamic and increasingly exposed to disturbance, making perpetual outcomes difficult to guarantee. Many offset programs rely on fixed durations and static assumptions ill-suited to managing long-term risks, creating a structural misalignment between ecological permanence and the safeguards intended to secure it. We review risks to long-term durability across three domains (non-physical, physical, methodological) and provide a typology to assess permanence risks and strengthen offset governance. Credible, enduring offsets are achievable with robust risk management and adaptive governance aligned with ecological realities.
Learning lessons from over-crediting to ensure additionality in forest carbon credits
Nature Communications
Tom Swinfield, Abby Williams, David Coomes, Michael Dales, Patrick Ferris, Alejandro Guizar-Coutiño, James Hartup, Jody Holland, Sadiq Jaffer, Julia P. G. Jones, Miranda O. K. Lam, Srinivasan Keshav, Anil Madhavapeddy, Eleanor Toye-Scott, Thales A. P. West, Andrew Balmford
April 2026
Independent evaluations have shown substantial over-issuance of REDD+ (Reducing Emissions from Deforestation and Degradation) credits traded on the voluntary carbon market. We synthesise these evaluations to estimate the additional forest conservation achieved by first-generation REDD+ projects and to identify mechanisms underlying over-crediting. We combine six independent ex post evaluations of avoided deforestation covering 44 REDD+ projects. These evaluations show that most projects reduced deforestation, but that they claimed an aggregate of 10.7 times more avoided deforestation than is justified by independent estimates. This discrepancy is not driven by the choice of forest cover data, but by selection bias in projects’ control areas and modelling approaches. Although recent initiatives that transfer assessment to unconflicted parties and restrict methodological flexibility are critical, they are insufficient. Ex post certification against credible counterfactuals is necessary if carbon markets are to represent causal reductions in deforestation.
Five rules for scientifically credible nature markets
Nature Ecology & Evolution
Sophus O.S.E. zu Ermgassen, Tom Swinfield, Joseph W. Bull, Natalie E. Duffus, Andrew Macintosh, Martine Maron, Sebastian Theis, Thomas White, Megan C. Evans
January 2026
Nature markets are proliferating rapidly around the world, yet it is underacknowledged that they have been practised in various forms for decades. A large body of scientific research has shown that nature markets regularly do not achieve their environmental objectives and provides generalizable lessons to support their ongoing improvement. The scale of the biodiversity crisis and the enduring popularity of nature markets mean it is now critical to stop reproducing the same mistakes. Here we synthesize international research from the history of nature markets and summarize five rules that are necessary precursors for achieving their environmental aims. We propose a checklist for investors, policymakers and civil society to assess whether nature markets are likely to be delivering scientifically credible outcomes. We score the world’s largest nature markets against these rules and show that all face integrity risks. Lastly, we outline critical evidence-based actions that can be taken to push nature markets towards greater integrity.
Strengthening the integrity of REDD+ credits: objectively assessing counterfactual methods using placebos
Environmental Research Letters
E-Ping Rau, Jody Holland, Thomas Swinfield, Abby Williams, Srinivasan Keshav, David A. Coomes
October 2025
The financing of tropical forest conservation projects through the sale of carbon credits remains a key opportunity to curb forest loss. REDD+ projects generate credits by reducing forest loss within project areas compared with counterfactual areas that face similar pressures (known as 'additionality'). We present an evaluation approach based on placebo projects, where no REDD+ activities occur and project and counterfactual outcomes should not diverge. Comparing four pixel-matching methods across 27 placebo projects across the tropics, we find pixel-matching is reliable for estimating counterfactual deforestation when based on ex-post data, but forecasting ex-ante is much less reliable. Systematic placebo evaluation can accelerate development of more credible counterfactual methods, strengthening the integrity of nature-based carbon credits.
Time to fix the biodiversity leak
Science
Andrew Balmford, Thomas S. Ball, Ben Balmford, Ian J. Bateman, Graeme Buchanan, Gianluca Cerullo, Francisco d’Albertas, Alison Eyres, Ben Filewod, Brendan Fisher, Jonathan M. H. Green, Kyle S. Hemes, Jody Holland, Miranda S. Lam, Robin Naidoo, Alexander Pfaff, Taylor H. Ricketts, Fiona Sanderson, Timothy D. Searchinger, Bernardo B. N. Strassburg, Thomas Swinfield, David R. Williams
February 2025
As momentum builds behind hugely ambitious initiatives like the Global Biodiversity Framework (GBF) 30 x 30 target and the European Union’s (EU’s) Biodiversity and Forestry Strategies, there is a danger that hard-won local conservation gains will be dissipated through leakage, the displacement of human activities that harm biodiversity away from the site of an intervention to other places (1). These off-site damages may be less than on-site gains—in which case the action is still beneficial but less so than it superficially seems. However, if activities are displaced to more biodiverse (or less productive) places, leakage impacts may exceed local benefits, so that well-intentioned efforts cause net harm. There is a pressing need for leakage effects like this to be acknowledged and as far as possible avoided or mitigated—through demand reduction, careful selection of conservation or restoration sites, or compensatory increases in production in lower-impact areas.
Mitigating risk of credit reversal in nature-based climate solutions by optimally anticipating carbon release
Carbon Management
E-Ping Rau, James Gross, David Anthony Coomes, Thomas Swinfield, Anil Madhavapeddy, Andrew Balmford, Srinivasan Keshav
August 2024
Nature-based climate solutions supply carbon credits generated from net carbon drawdown in exchange for project funding, but their credibility is challenged by the inherent variability and impermanence of drawdown. By evaluating drawdown benefits from a social cost of carbon perspective, project developers can enhance credibility and estimate impermanence by conservatively anticipating drawdowns to be eventually released following a release schedule, issuing additional credits when actual release is less severe than anticipated. We demonstrate how we can use ex post observations of drawdowns to construct optimal release schedules that limit the risk of credit reversals (when net drawdown is negative). We simulate both theoretical and real-life projects to examine how this approach balances the trade-off between generating credits evaluated as more permanent and limiting reversal risk. We discuss how this approach incentivizes project performance and provides a pragmatic solution to challenges facing larger-scale implementation of nature-based climate solutions.
Nature-based credit markets at a crossroads
Nature Sustainability
Tom Swinfield, Siddarth Shrikanth, Joseph W. Bull, Anil Madhavapeddy, Sophus O.S.E. zu Ermgassen
August 2024
Continuing to produce nature-based credits using dubious accounting methodologies will yield limited carbon and biodiversity gains. Establishing scientific credibility unlocks the potential of credits to meaningfully contribute to targets of the Paris and Kunming-Montreal agreements.
A call to develop carbon credits for second-growth forests
Nature Ecology & Evolution
Pedro H. S. Brancalion, Andrew Balmford, Charlotte E. Wheeler, Ricardo R. Rodrigues, Bernardo B. N. Strassburg, Tom Swinfield
January 2024
Natural climate solutions have gained momentum as being central to mitigating climate change while generating co-benefits for nature and people1. Among the solutions that are available, tropical reforestation is second only to avoided forest conversion in terms of cost-effectiveness2. Initiatives such as the Bonn Challenge, the Trillion Tree Campaign and the United Nations’ Decade on Ecosystem Restoration have established ambitious commitments for forest landscape restoration, mostly for tropical regions. Although different approaches can be used to increase tree cover in deforested landscapes, there is a large body of evidence that natural forest regrowth is the most viable option3. But in spite of the enormous potential, the fact that many second-growth forests in human-modified landscapes are extremely short-lived has undermined their contribution to mitigating climate change and biodiversity loss.
Realizing the social value of impermanent carbon credits
Nature Climate Change
Andrew Balmford, Srinivasan Keshav, Frank Venmans, David Coomes, Ben Groom, Anil Madhavapeddy, Tom Swinfield
October 2023
Efforts to avert dangerous climate change by conserving and restoring natural habitats are hampered by concerns over the credibility of methods used to quantify their long-term impacts. Here we develop a flexible framework for estimating the net social benefit of impermanent nature-based interventions that integrates three substantial advances: (1) conceptualizing the permanence of a project’s impact as its additionality over time; (2) risk-averse estimation of the social cost of future reversals of carbon gains; and (3) post-credit monitoring to correct errors in deliberately pessimistic release forecasts. Our framework generates incentives for safeguarding already credited carbon while enabling would-be investors to make like-for-like comparisons of diverse carbon projects. Preliminary analyses suggest nature-derived credits may be competitively priced even after adjusting for impermanence.
Credit credibility threatens forests
Science
Andrew Balmford, Pedro H. S. Brancalion, David Coomes, Ben Filewod, Ben Groom, Alejandro Guizar-Coutiño, Julia P. G. Jones, Srinivasan Keshav, Andreas Kontoleon, Anil Madhavapeddy
May 2023
Perspective noting that failures in credit credibility for forest carbon projects threaten their conservation benefits.
A global evaluation of the effectiveness of voluntary REDD+ projects at reducing deforestation and degradation in the moist tropics
Conservation Biology
Alejandro Guizar-Coutiño, Julia P. G. Jones, Andrew Balmford, Rachel Carmenta, David A. Coomes
September 2022
Reducing emissions from deforestation and forest degradation (REDD+) projects aim to contribute to climate change mitigation by protecting and enhancing carbon stocks in tropical forests, but there have been no systematic global evaluations of their impact. We used a new data set for tropical humid forests and a standardized evaluation approach (based on pixel matching) to quantify the performance of a representative sample of 40 voluntary REDD+ projects in 9 countries certified under the Verified Carbon Standard (VCS). In the first 5 years of implementation, deforestation within project areas was reduced by 47% (95% confidence interval [CI]: 24–68) compared with matched counterfactual pixels, and degradation rates were 58% lower (95% CI: 49–63). Reductions were small in absolute terms but greater in sites located in high-deforestation settings and did not appear to be substantially undermined by leakage activities in forested areas within 10 km of project boundaries. At the 26th Conference of the Parties of the United Nations Framework Convention on Climate Change, the international community renewed its commitment to tackling tropical deforestation as a nature-based solution to climate change. Our results indicate that incentivizing forest conservation through voluntary site-based projects can slow tropical deforestation and highlight the particular importance of prioritizing financing for areas at greater risk of deforestation.