NASA Carbon Monitoring Systems estimation of the net ecosystem exchange of carbon dioxide in 2003. Ecosystems absorb about 25 percent of human carbon dioxide emissions each year. During photosynthesis, plants absorb carbon dioxide and release it during respiration. This process, known as net ecosystem exchange, helps reduce atmospheric carbon dioxide concentrations. Global patterns of net ecosystem exchange show seasonal variations in vegetation, with plants absorbing more carbon during the spring and summer growing seasons, and releasing much of this carbon back into the atmosphere during the autumn and winter months. Understanding the amount of carbon absorbed by ecosystems and how this may change in the face of increasing extreme weather associated with climate change is a significant goal for scientists. The scale represents kilograms of carbon dioxide per 100 square metres per month and ranges from -10 to 10. Data obtained by the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) satellites.