Tropical forests play a crucial role in Earth’s climate system by absorbing atmospheric carbon dioxide. However, accurately measuring the amount of carbon they absorb, store, and release is a complex task due to variations in measurement and reporting methods. This is particularly important as nations assess their efforts to combat the climate crisis. Fortunately, a recent study published in Carbon Balance and Management sheds light on how differences in carbon flux estimates associated with human activity can be reconciled.

Carbon flux refers to the net carbon exchange between forests and the atmosphere over a period. It is calculated by balancing the carbon emitted and the carbon sequestered by forests per hectare. Earth-observing satellites provide valuable independent information on how forests change over time, allowing scientists to estimate carbon flux rates. These estimates can then be compared to the results reported in National Greenhouse Gas Inventories (NGHGIs).

However, the study highlights discrepancies between satellite-based estimates and NGHGI data. For example, in Brazil, satellite data indicated the country had a net carbon sink between 2001 and 2020. In contrast, the NGHGI reported that human activity resulted in Brazilian forests being a net carbon source. A carbon source releases more carbon than it absorbs, while a carbon sink absorbs more carbon.

The discrepancies arise because satellites cannot distinguish between managed and natural forests, whereas national reports can define certain forest areas as managed. The research team focused on three case studies to address this issue: Brazil, Indonesia, and Malaysia. By adjusting the satellite estimates to align with the definition of managed forests in the Brazilian NGHGI, the study found that the net carbon flux estimates became comparable to those reported in the inventory.

In Indonesia, the satellite and inventory estimates of net carbon flux were similar, indicating that the forests were a carbon source. However, in Malaysia, there was a significant difference. The inventory reported that the forests were a carbon sink, while the satellite data indicated they were a carbon source.

The study emphasizes the importance of enhanced transparency and alignment between different approaches for independent measuring and verification, as outlined in the Paris Agreement. By addressing uncertainties and inaccuracies, researchers can reconcile diverging estimates and provide more accurate assessments of carbon flux from tropical forests.

This research has significant implications for understanding regional carbon budgets and supporting efforts to combat climate change. By improving the comparability between satellite-based estimates and NGHGIs, scientists can better assess the effectiveness of carbon mitigation strategies and inform policy decisions.

References

• European Space Agency. (2023, December 7). Minding the gap on tropical forest carbon: Reconciling data from Earth-observing satellites with national reporting. Phys.Org; European Space Agency. https://phys.org/news/2023-12-minding-gap-tropical-forest-carbon.html
• Heinrich, V., House, J., Gibbs, D. A., Harris, N., Herold, M., Grassi, G., Cantinho, R., Rosan, T. M., Zimbres, B., Shimbo, J. Z., Melo, J., Hales, T., Sitch, S., & Aragão, L. E. O. C. (2023). Mind the gap: Reconciling tropical forest carbon flux estimates from earth observation and national reporting requires transparency. Carbon Balance and Management, 18(1), 22. https://doi.org/10.1186/s13021-023-00240-2