Researchers from more than 60 countries have used measurements from NASA’s Orbiting Carbon Observatory-2 (OCO-2) mission and a network of surface-based observations to estimate carbon dioxide emissions and removals in more than 100 countries. The study, published in Earth System Science Data, offers a top-down approach to quantify increases and decreases in atmospheric carbon dioxide concentrations from 2015 to 2020, providing valuable insights into the carbon dioxide being emitted and absorbed by forests and other carbon sinks in these countries.
“NASA is focused on delivering Earth science data that addresses real-world climate challenges—like helping governments around the world measure the impact of their carbon mitigation efforts,” said Karen St. Germain, director of NASA’s Earth Science Division at NASA Headquarters in Washington. “This is one example of how NASA is developing and enhancing efforts to measure carbon emissions in a way that meets user needs.”
Benefits of Space-Based Tools
This pilot project demonstrates how space-based tools can support insights on Earth as nations work to achieve their climate goals. Although the OCO-2 mission was not designed to estimate emissions from individual nations, the findings come at an opportune time as the first Global Stocktake to assess the world’s collective progress toward limiting global warming, as specified in the 2015 Paris Agreement, is scheduled for 2023.
Top-Down vs. Bottom-Up Approaches
Traditionally, carbon measurements have relied on bottom-up approaches that tally and estimate the amount of carbon dioxide being emitted across all sectors of an economy, such as transportation and agriculture. While bottom-up carbon inventories are critical for assessing progress toward emission-reduction efforts, they require significant resources, expertise, and knowledge of the extent of the relevant activities.
In contrast, the top-down approach developed by this study provides a new perspective by tracking both fossil fuel emissions and the total carbon “stock” changes in ecosystems, including trees, shrubs, and soils. This method could be especially helpful for nations that lack traditional resources for inventory development. The researchers’ findings include data from more than 50 countries that have not reported emissions for at least the past 10 years.
“Our top-down estimates provide an independent estimate of these emissions and removals, so although they cannot replace the detailed process understanding of traditional bottom-up methods, we can check both approaches for consistency,” said Philippe Ciais, a study author and research director at the Laboratoire des Sciences du Climat et de l’Environnement in France.
Understanding Carbon Fluctuations
The study provides valuable data for tracking carbon dioxide fluctuations related to land cover change, with emissions from deforestation making up a disproportionate amount of total carbon output in the Global South. In other parts of the world, the findings indicate some reductions in atmospheric carbon concentrations via improved land stewardship and reforestation.
Challenges of Bottom-Up Approaches
While bottom-up methods for estimating carbon dioxide emissions and removals from ecosystems are essential, they are vulnerable to uncertainty when data is lacking or the net effects of specific activities, such as logging, aren’t fully known. The top-down estimates in this study provide an independent estimate of these emissions and removals, which can be used to check the consistency of both approaches.
Lead author Brendan Byrne, a scientist at NASA’s Jet Propulsion Laboratory in Southern California, said continued observations from OCO-2 and surface sites will allow researchers to track how these emissions and removals change as the Paris Agreement is implemented. Future international missions that provide an expanded mapping of CO2 concentrations across the globe will allow for more precise estimates of countries’ emissions and removals.