Understanding the importance of monitoring carbon levels in tropical forests

Tropical forests play an important role in Earth’s climate system by absorbing carbon from the atmosphere. However, accurately measuring and reporting the amount of carbon they absorb, store, and release is a complex task due to variations in measurement methods. This information is vital for nations to assess their efforts in combating the climate crisis. Fortunately, new research has shed light on how differences in estimates of carbon flux associated with human activity can be reconciled.

Published in the Carbon Balance and Management journal, the research explains why there can be a discrepancy between carbon flux estimates based on data from Earth observing satellites and country estimates provided in National Greenhouse Gas Inventories. Net forest carbon flux refers to the net exchange of carbon between forests and the atmosphere, calculated as the balance between carbon emitted and carbon sequestered by forests per hectare over a specific period. Satellites offer independent information on how forests change over time, allowing for the estimation of carbon flux rates. These measurements can then be compared to the results reported in National Greenhouse Gas Inventories. However, this approach sometimes leads to discrepancies.

The study highlights the case of Brazil, where Earth observation data indicated that the country was a net carbon sink between 2001 and 2020. This contrasts with the country’s inventory, which showed that human activity resulted in forests being a net carbon source. A carbon source releases more carbon than it absorbs, often due to activities such as deforestation, logging, and fires. On the other hand, a carbon sink absorbs more carbon from the atmosphere than it releases, primarily through the growth of standing forests and the restoration of new forests.

Viola Heinrich, the lead author of the paper from the University of Bristol and the German Research Centre for Geoscience, explains that discrepancies between satellite data and inventories can arise from whether a piece of land is considered managed by humans or natural. Satellites cannot distinguish this distinction, while national reports can define an area of forest as managed. By adjusting the satellite estimates to align with the definition of managed forests in the Brazilian National Greenhouse Gas Inventory, the net flux of carbon dioxide per year became a source of +0.6 Gt, aligning with the inventory’s estimate.

The research team also examined Indonesia and Malaysia as case studies. In Indonesia, the satellite data and inventory net flux estimates were similar, both indicating a source of +0.6 Gt of carbon dioxide per year. However, in Malaysia, there was a significant difference. The inventory stated that their forests were a sink at -0.2 Gt carbon dioxide per year, while the satellite data suggested they were a source of +0.2 Gt carbon dioxide per year. Dr. Heinrich suggests that uncertainties and inaccuracies, along with different approaches, may explain these divergences.

The study emphasizes the need for enhanced transparency to align different approaches for independent measuring and verification, as outlined in the Paris Agreement. This finding has significant implications for projects like ESA’s Climate Change Initiative Regional Carbon Cycle Assessment and Processes Phase-2 (RECCAP-2). The project aims to analyze regional carbon budgets using top-down atmospheric inversion and bottom-up data-driven models. By implementing a similar approach to the one outlined in the research, better reconciliation between top-down inversions and National Greenhouse Gas Inventories can be achieved.

In conclusion, this research highlights the challenges in accurately estimating carbon flux associated with human activity in tropical forests. By reconciling discrepancies between satellite data and inventories, nations can have a more accurate understanding of their carbon sequestration efforts. Enhanced transparency and alignment of different measurement approaches are crucial for effective climate action. Ultimately, this knowledge will contribute to better decision-making and policy development in combating the climate crisis.