Tracking carbon sinks from space — the application of GIS in the voluntary offset market

BeZero Carbon
Aug 2 · 4 min read

Sujit Ghosh, BeZero’s Lead GIS Analyst, describes the role of GIS in monitoring the performance of nature-based carbon offset projects.

  • Nature-based projects made up almost 37% of total accredited issuance in the last 10 years.
  • The performance of these projects is often not adequately reviewed in situ.
  • The BeZero Carbon Rating incorporates Geographic Information Systems (GIS) to critically review project performance of nature-based offsets.

Seeing the carbon for the trees

Forests sink around 2.4 billion tonnes of carbon per year from atmosphere¹. However, due to deforestation and degradation, these natural reservoirs of carbon can also switch to sources of carbon². Therefore, the effective and continual management of forests plays a crucial role in climate change mitigation.

Currently, nature-based carbon offset projects dominate credit issuances in the voluntary offset market (Chart 1). Such carbon credits are an integral part of corporate and governmental plans to achieve net zero emissions goals, making the performance of the nature-based carbon offset projects vital to the success of these broader goals. However, poor project performance in terms of true emission reduction is increasingly being highlighted³.

Projects must be objectively and rigorously reviewed to ensure offsets are delivering on their carbon promises. Geographic Information System (GIS) combined with satellite remote sensing is a powerful tool for the accurate estimation of forest cover and forest carbon content, enabling the verification of data presented by the carbon offset projects.

Chart 1. Carbon credits issued (in millions) per sector to date from Berkeley Voluntary Registry Offsets Database⁴.

Reading between the baselines

The number of carbon credits issued to a project depends on the selection of a baseline scenario. Where for some projects, baselines may be set relatively easily, in others, baseline setting can be a source of contention.

For example, in REDD+ projects, baselines are set by identifying historical deforestation rates within the project boundary and the surrounding, or reference, area. However, by selecting reference areas that aren’t reflective of the same drivers of deforestation or with wider forest frontiers which are more prone to logging, baselines can be falsely inflated.

Adopting inflated baselines leads to over-crediting, a key risk identified in the BeZero Carbon Rating. We apply GIS to analyse this risk in nature-based projects. For example, for REDD+ projects we review the size and relevance of the reference area, the broader drivers of deforestation in the area and the pre-project baseline scenarios for land use. All of these can be used to assess the appropriateness of the baseline and subsequent carbon performance reported.

If a tree falls in the forest, it makes a sound in space

Carbon credits for most accredited nature-based projects are issued ex-post — that is following a monitoring and verification process to check the carbon has been avoided or sequestered. Despite these audit processes being in place, projects often exhibit discrepancies — in carbon calculations, in numbers of credits issued between reports, and reporting of unplanned forest loss activities within project and leakage areas. Applying an additional layer of scrutiny through our application of GIS in the BCR is crucial to assessing the effectiveness of those credits issued.

Quantification of the forest cover change in the project area is a straightforward measurement process. It can be easily done through analyses of annual land cover data prepared from satellite images. Following acquisition of annual forest cover data, changes can be detected and quantified by investigating the difference in forest cover between consecutive years.

Carbon stocks however, cannot be directly estimated from satellite data. This is done in two steps. First, a regression model must be built using biomass data on the ground and the satellite data parameters for related locations. Second, the model is extended to predict the biomass for the whole project area using satellite data parameters. Once the information about change in forest cover and biomass per unit area is known, the change in carbon stock can be easily measured.

The main challenge in biomass estimation for offset projects is that proper field biomass data with accurate locations is rarely available for accurate modelling. This creates obstacles in comparing the project reported data with independent biomass estimations.

Monitoring past and present

At BeZero, the GIS team is working on multiple aspects for the monitoring of nature-based offset projects. We have estimated the carbon stocks for various types of nature-based offset projects which can be directly compared with the reported project data. In addition to validating historical data and annual project performance, we are using GIS to alert us to significant changes on the ground in almost real time. These processes are already being established for lands unrelated to the offset market.

Independent ground-truthing of offset projects will enable accountability of risks such as additionality, leakage, over-crediting and permanence. These details are essential to evaluate the BCR’s core question of whether a credit is achieving a tonne of carbon removed or avoided.

Written by Sujit Ghosh, Lead GIS Analyst.


  1. Pan et al (2011)
  2. Houghton et al (2009)
  3. Clarke & Barrett (2021)
  4. Berkeley Voluntary Registry Offsets Database

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