2011 AMS Summer Community Meeting
National Center for Atmospheric Research
Center Green Conference Center · Boulder, Colorado
8–11 August 2011
Measuring Atmospheric Carbon Dioxide from Space
Chip Miller for the OCO-2 Team
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
Fossil fuel combustion, deforestation, and other human activities are currently emitting more than 30
billion tons of carbon dioxide (CO2) into the atmosphere each year. Precise measurements of
atmospheric CO2 from a global network of surface stations show that these emissions are superimposed
on an active carbon cycle, driven by natural processes in the land biosphere and oceans. These
processes emit more than 20 times as much CO2 into the atmosphere each year as human activities, and
then reabsorb a comparable amount, along with about half of the human contributions. While existing
ground-based measurements provide a strong integral constraint on both human and natural CO2 fluxes
into the atmosphere, a far more comprehensive measurement network is needed to clearly discriminate
the human CO2 emissions from the natural background. Such measurements are essential to monitor
compliance with CO2 emissions regulations and to assess the efficacy of CO2 emission reduction
strategies.
Recent advances in space based remote sensing observations of CO2 and other greenhouse gases hold
substantial promise for future global monitoring efforts. The space based observations are expected to
complement, rather than replace surface greenhouse gas measurements by providing improved spatial
coverage and sampling densities. At least initially, their greatest benefits are expected over ocean
basins and over tropical continents, where the ground based network is still quite sparse.
Measurements of the absorption of reflected sunlight by CO2 are ideal for this application because they
can be analyzed to yield estimates of the column averaged CO2 dry air mole fraction that are most
sensitive to CO2 variations near the surface, where most CO2 sources and sinks are located. The
Japanese Greenhouse Gases Observing Satellite, GOSAT, is the first satellite designed specifically for this
application. GOSAT has been collecting CO2 and methane (CH4) observations over the sunlit hemisphere
since April 2009. These data are beginning to yield new insights into the carbon cycle. The NASA
Orbiting Carbon Observatory – 2 (OCO-2), is the next dedicated CO2 monitoring satellite. OCO-2 is
currently under development in preparation for a launch as early as 2013. Other CO2 monitoring
satellites, including the CNES MicroCarb, the European Space Agency’s CarbonSat, and GOSAT-2 are in
the planning stages. If all goes as planned, by the end of this decade, we will have a coordinated global
network of surface and space-based CO2 monitoring systems, whose data can be assimilated
sophisticated models to provide a far more complete description of the processes controlling the
buildup of atmospheric CO2.