NASA researchers have added an important piece to our understanding of how carbon dioxide circulates through Earth’s atmosphere and how this cycle changes throughout the year.
Carbon dioxide levels in the atmosphere are not constant. Instead, they fluctuate with the seasons as the planet’s ecosystems absorb and release CO₂. In effect, the Earth “breathes” carbon dioxide over the course of the year.
A team of NASA scientists has now analyzed two years of data from the agency’s Orbiting Carbon Observatory-2 (OCO-2) satellite. Launched on July 2, 2014, the satellite measures carbon dioxide in the atmosphere by observing how sunlight reflects off CO₂ molecules in the air column, using three different spectral bands.
The findings, published in Science, reveal detailed patterns of carbon dioxide movement across the Northern Hemisphere. The data shows when and where photosynthesis occurs, as plants absorb carbon dioxide from the atmosphere.
To visualize these changes, researchers used a computer model known as GEOS-5, developed by scientists at NASA’s Goddard Space Flight Center in the Global Modeling and Assimilation Office.
When combined with ground-based observations, satellite measurements provide a much clearer picture of the global carbon cycle. The data reveals where atmospheric carbon dioxide concentrations rise and fall during different seasons.
For example, carbon dioxide builds up in the Northern Hemisphere during winter, when plant activity is low. As spring arrives and vegetation begins to grow, photosynthesis rapidly absorbs CO₂, causing atmospheric levels to decline. The satellite captured these seasonal changes in unprecedented detail.
The highest concentrations of carbon dioxide are found over cities, which account for more than 70 percent of human CO₂ emissions. OCO-2 is sensitive enough to detect differences not only between urban and rural areas, but even within cities themselves.
This carbon dioxide visualization was produced by a computer model called GEOS-5, created by scientists at NASA Goddard Space Flight Center’s Global Modeling and Assimilation Office.
The satellite can also observe regional events such as biomass burning in Africa, which produces clear increases in atmospheric carbon dioxide.
The goal of the research is to better understand how human activity is altering Earth’s climate system. In the future, this data may help scientists improve regional agricultural practices and detect early signs of drought.
The OCO-2 dataset now allows researchers to analyze regional sources and sinks of carbon dioxide across the globe.
A follow-up mission, OCO-3, was planned for launch in 2018 to be installed on the International Space Station. The instrument was designed to further study how carbon dioxide is distributed across the planet, particularly in relation to growing urban populations and changing patterns of fossil-fuel use.
Reference:
Eldering, A. et al. “The Orbiting Carbon Observatory-2 early science investigations of regional carbon dioxide fluxes.” Science, October 13. DOI: 10.1126/science.aam5745.