Nature-based carbon accounting: How “integrity” has evolved, and what still matters

Nature-based carbon projects have operated for more than 25 years. Early assumptions that greenhouse gas accounting would be simple have proven wrong. What has occurred instead is a steady evolution of integrity, as accounting weaknesses have been identified and progressively addressed.

The problem is not measuring carbon stocks…

There is a persistent misconception that integrity failures in nature-based carbon stem primarily from poor measurement: “All we need is to measure the trees better.” In reality, the science of carbon measurement in trees, soils, and other pools is well established with high accuracy and quantifiable uncertainty. In addition, tools such as LiDAR and other remote sensing are increasingly emerging, which overcome issues with the cost and complexity of extensive sampling. 

In other words,  the real integrity problems are not related to the physical measurement of carbon. Rather, they are in regard to baseline, additionality, leakage, and permanence, each of which has no “direct tape-measure related” solution.

…but rather carbon baselines, due to their counterfactual nature

Would trees have been planted or grown anyway? Would timber have really been harvested as claimed? How many hectares would really have been deforested?

Baselines are inherently counterfactual. Once a project begins, the “without project” scenario can never be observed directly.  This challenge applies for all project types, not just nature-based. The Clean Development Mechanism (CDM) when it launched nearly two decades ago initiated solutions through a set of tests on regulatory requirements, barriers, economics and common practice to show the most likely “without project” baseline. But these approaches proved too subjective and sensitive to creative selection of data, and often inadequate to reliably distinguish genuinely additional projects – e.g., projects for which the project scenario represents a true gain from the most plausible baseline. 

Several recent developments have materially strengthened baseline integrity, including:

• Linking project baselines to jurisdictional trends, so that total deforestation, harvesting or planting across an area cannot exceed what is observed historically, reducing the risk of over-crediting at scale. 
• Dynamic baselines, wherein additionality is assessed over time based on what is actually happening on comparable surrounding land, rather than being fixed at the start of a project.  These approaches strengthen integrity, but they also shift more risk and uncertainty onto projects and their investors.

Leakage and permanence also remain thorny issues

Leakage refers to emissions being displaced outside a project’s boundary, rather than avoided altogether. This remains difficult to address because the effects can be indirect, spread over large areas, or driven by wider market dynamics rather than local actions alone. Early approaches relied heavily on generic discount factors that were often poorly suited to specific geographies or activities, and difficult to defend in practice. Over time, more credible approaches have focused less on accounting assumptions and more on real-world mitigation — for example, maintaining commodity production so that pressure is not simply shifted elsewhere.

Permanence has been the most persistent concern associated with nature-based carbon projects. Because carbon stored in ecosystems can be reversed by fire, disease, or land-use change, critics have questioned whether these projects can deliver climate value over meaningful timeframes.

One solution is to create credits with an expiration date. The CDM tried this with little success: few wanted to buy. Others have required long-term legal protections attached to deeds that landowners naturally objected to.

Over time, the market has shifted away from rigid notions of permanence toward managing the durability of carbon storage through explicit risk management. The dominant approach has been pooled buffer reserves managed by crediting programmes. While these mechanisms have improved confidence, they are not universally accepted as sufficient on their own.

New models are now emerging, including commercial insurance, replacement units, and financial structures that manage long-term liability while allowing projects to sell credits at market value. Together, these approaches reflect a broader shift from attempting to eliminate reversal risk to recognising, managing, and compensating for it transparently.

Integrity is built over time, not achieved all at once 

Integrity in nature-based carbon is a continual process rather than a fixed end point. Early approaches were often untested, and it has only been through years of application, scrutiny, and advancing science that weaknesses have been identified and addressed. Today’s credits will not be the final word, nor should they be. Progress depends on recognising imperfection, responding quickly to emerging risks, and continuing to strengthen approaches as evidence and experience evolve.

The Conversations on Integrity in Nature-Based Carbon series will return to many of these topics covered here for more in depth exploration of strengths, weaknesses and future directions.