NASA Missions to Study the Global Carbon Cycle and Climate
Over the years, several NASA missions have studied various aspects of biology and climate. These studies have been augmented by data from operational weather satellites of the National Oceanic and Atmospheric Administration (NOAA).

The Landsat series of satellites, beginning in 1972, is the United States’ oldest land-surface observation system. Landsat images have been used to study a wide range of processes, such as urban sprawl, deforestation, agricultural land-use trends, glaciation, and volcanic activity. The latest in the series, Landsat 7, launched in April 1999, is continuing to provide essential land-surface data to the scientific community. The Landsat 7 system is collecting and archiving an unprecedented quantity of high-quality multispectral data each day. These new data are providing a high-resolution view of both seasonal and interannual changes in the terrestrial environment.

Instrumetns aboard the Landsat satellites measure vegetation at high resolution. The Multi-Spectral Scanner acquired this image of eastern Australia on December 9, 1982. Green indicates increasing density of vegetation. [Image courtesy Commonwealth Scientific & Industrial Research Organization (Australia)]

The launch of the Advanced Very High Resolution Radiometer (AVHRR) on TIROS-N in 1978, and on subsequent NOAA operational satellites, permitted the global mapping of sea surface temperature and vegetation. The launch of the Coastal Zone Color Scanner (CZCS) on Nimbus-7, also in 1978, made mapping oceanic chlorophyll and phytoplankton possible. The first step of photosynthesis both on land and in the oceans is the absorption of the sun’s energy by the chlorophyll in leaves and phytoplankton. Scientist can measure the absorption of the sun’s energy from space with satellites and consequently estimate the rates of carbon dioxide uptake by photosynthesis. Scientists at NASA’s Goddard Space Flight Center produced the “First Picture of the Global Biosphere” using images from 15,000 orbits of the NOAA-7/AVHRR (for estimating land chlorophyll) and 66,000 images from the Nimbus-7/CZCS (for estimating oceanic phytoplankton chlorophyll referred to as “ocean color”).

The fist global image of the Earth’s biosphere was created by NASA scientists using ocean data from the Coastal Zone Color Scanner (CZCS) and land data from the Advanced Very High Resolution Radiometer (AVHRR). Altogether, the data took almost 8 years to compile. Current satellite instruments like the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) and can produce images like this roughly once a week. (Image courtesy NASA GSFC)

Launched in August 1997 as a successor to the CZCS, the SeaWiFS instrument onboard the OrbView-2 satellite acquires ocean color data to study the role of the oceans in the global carbon cycle, fluxes of trace gases at the air-sea interface, and ocean primary productivity (rate of carbon fixation from the atmosphere). As was learned from CZCS, subtle changes in ocean color signify various types and quantities of marine phytoplankton. Ocean color data from SeaWiFS are helping scientists identify ocean “hot spots” of biological activity, measure global phytoplankton biomass, and estimate the rate of oceanic carbon uptake. This information will yield a better understanding of the sources and sinks of the carbon cycle and the processes that shape global climate and environmental change.

Synthetic aperture radars on European, Japanese, and Canadian satellites, as well as NASA’s Space Shuttle monitor deforestation and surface hydrological states and processes. The ability of synthetic aperture radars to penetrate cloud cover and dense plant canopies make them particularly valuable in rainforest and high-latitude boreal forest studies.

With the launch of the flagship EOS satellite in 1999—Terra—NASA is extending the measurements of ocean color and land vegetation with advanced spaceborne instruments. EOS instruments such as the Multi-Angle Imaging SpectroRadiometer (MISR) and the Moderate-Resolution Imaging SpectroRadiometer (MODIS) are providing global maps of surface vegetation so that scientists can model the exchange of trace gases, water, and energy between vegetation and the atmosphere. The Enhanced Thematic Mapper Plus (ETM+) onboard Landsat 7 and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard EOS Terra are providing simultaneous multispectral, high-resolution observations of surface composition and natural hazards (volcanoes, floods, drought, etc.). In addition, MISR’s ability to correct land-surface images for atmospheric scattering and absorption and sun-sensor geometry will allow better calculation of vegetation properties. The MOPITT (Measurements of Pollution in the Troposphere) instrument on Terra is providing global measurements of tropospheric methane and carbon monoxide.

New satellite sensors provide new ways of looking at Earth. In addition to measuring vegetation density, MODIS can also measure photosynthetic activity. This provides a more accurate estimate of the amount of carbon absorbed by plants. The image above shows photosynthetic activity during December 2000. Increasingly dark green indicates higher carbon consumption. (Image courtesy Peter Votava, University of Montana)

In addition to satellite and airborne missions, NASA, along with its international partners, conducts large-scale experiments in different types of vegetation (forests, grasslands, etc.) to build a better understanding of the carbon cycle.

The Boreal Ecosystem-Atmosphere Study (BOREAS) was a major international research program sponsored by NASA’s Goddard Space Flight Center and carried out in the Canadian boreal forest. Its primary goals were to determine how the boreal forest interacts with the atmosphere (via the transfer of gases and energy), how much carbon is stored in the forest ecosystem, how climate change will affect the forest, and how changes in the forest affect weather and climate. Primarily conducted from 1994-1996 (with some experiments still continuing), BOREAS integrated ground, tower, airborne, and satellite measurements of the interactions between the forest ecosystem and the lower atmosphere. The findings from BOREAS are now being released.

The Large-Scale Biosphere-Atmosphere Experiment (LBA) is an international research initiative led by Brazil. It is designed to create new knowledge needed to understand the climatological, ecological, biogeochemical, and hydrological functioning of Amazonia, the impact of land-use change on these functions, and the interactions between Amazonia and the Earth system. The Amazon basin contains a large store of carbon, which may be exchanged with the atmosphere through (i) changes in land use brought about by fire, clearing, logging, planting and re-growth and (ii) changes in the balance between photosynthesis and respiration occurring as a result of variations in climate and atmospheric chemistry. Both types of change introduce uncertainties in the global carbon balance.

A major challenge for research within LBA is to determine both the human management-induced components and the climate-induced components of the net flux of carbon in the Amazon Basin. Of the 100 projects within LBA, 25 of them focus on understanding carbon exchange and storage throughout the Amazon. A new campaign will be launched in 2002 to complement in situ field and space-based system observations with airborne measurements of atmospheric gases and vegetation imaging.

Collectively, the resulting accurate, self-consistent, and long-term data sets from these NASA missions and campaigns are expected to lead to major advances in our understanding of the role of the global biosphere in climate change.

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The Carbon Cycle

Introduction
Biological/Physical Carbon Cycle: Photosynthesis and Respiration
Carbon on the Land and in the Oceans: The modern carbon cycle
The Human Role
NASA Missions to Study the Global Carbon Cycle and Climate
References