Net Ecosystem Exchange of Carbon Dioxide

Each year, ecosystems absorb about 25% of human carbon dioxide emissions, providing an invaluable mitigation that has substantially slowed the rate of climate change. Carbon dioxide is absorbed by plants during photosynthesis and released during respiration, a process with occurs in both plants and soils. The balance of this absorption and release, called net ecosystem exchange, serves to reduce atmospheric carbon dioxide concentrations. However, understanding how much carbon is absorbed by ecosystems and how this may change in a future faced with increases in extreme weather associated with climate change is a major challenge for scientists. Despite the critical importance of ecosystem-atmosphere carbon dioxide exchange, which scientists call flux, directly measuring the global exchange of carbon dioxide molecules is not possible. Satellite observations of vegetation, from satellite instruments like the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), provide valuable information that can be combined with computer models to provide realistic, observationally based estimates of carbon flux and track how underlying processes change over time.



This visualization shows net ecosystem exchange calculated by the Carnegie-Ames-Stanford-Approach – Global Fire Emissions Database version 3 (CASA-GFED3), a simple model that combines AVHRR and MODIS data with estimates of temperature and precipitation from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Global patterns of net ecosystem exchange reflect seasonal changes in vegetation with plants absorbing more carbon during spring and summer growing seasons and releasing much of this carbon back to the atmosphere during fall and winter months. The nearly 20-year record of CASA-GFED3 data also reflects interannual variability in carbon flux that can result from unusual climate patterns like droughts. Scientists across the world use the CASA-GFED3 data as input to atmospheric models, which then use satellite observations to evaluate and further refine the flux estimates. This understanding, supported by NASA’s Carbon Monitoring System, helps scientists improve the representation of vegetation in climate model predictions and provides actionable information about the processes controlling greenhouse gas concentrations to policymakers.