Launched in 2014, the Orbiting Carbon Observatory-2 (OCO-2) has been collecting NASA’s first detailed, global measurements of carbon dioxide in the atmosphere. The OCO-2 team recently released its first full year of data, which is critical to analyzing and understanding Earth’s carbon cycle.
The animated map above shows global average carbon dioxide concentrations as measured by OCO-2 from September 6, 2014, to September 6, 2015. The satellite measures carbon dioxide from the top of Earth’s atmosphere to its surface. Higher concentrations appear dark orange, while lower concentrations appear yellow. The scale is relatively narrow, from 390 to 405 parts per million, the high and low measurements by OCO-2 in its first year. Since the beginning of the industrial age, the global concentration of CO2 has increased from roughly an average of 280 parts per million to an average of 400 parts per million.
One recognizable pattern over the year is the annual uptake and release of carbon as each hemisphere passes through the seasons. In the winter, carbon dioxide levels are at their peak in the northern hemisphere, when there is little plant or phytoplankton growth to offset emissions from human activities and natural sources. At the same time, CO2 concentrations drop in the southern hemisphere, which is bathed in summer sunlight and heat. The pattern reverses as the hemispheres change seasons. According to the new measurements, atmospheric CO2 changes by 8 to 12 parts per million (2 to 3 percent) from winter through the “spring drawdown” in the northern hemisphere. This is visible in the maps below from March-April and August 2015.
Over the course of a year, it is also clear that CO2 levels are generally higher over the northern hemisphere—where there are more people and more emissions—than in the southern hemisphere. Both phenomena are well known to scientists, but OCO-2 now lets us see those patterns more clearly. Scientists expect that more patterns will emerge on finer scales as the OCO-2 data set grows with time.
Though atmospheric carbon has been measured from stations on the ground—most famously at Mauna Loa in Hawaii—the value of OCO-2 is that it makes consistent measurements with the same instrument over all land and sea surfaces. This was previously done, though at lower resolution and less frequency, by the Japanese GOSAT satellite. NASA’s Atmospheric Infrared Sounder on the Aqua satellite also senses carbon dioxide, though higher in the atmosphere.
OCO-2 is NASA’s first spacecraft dedicated to studying the manmade and natural sources and sinks of carbon dioxide from the top of the atmosphere to the surface. It uses high-resolution spectrometers that measure the intensity of sunlight at different wavelengths after it has passed down through the atmosphere, reflected off the land surface, and passed back up through the atmosphere. Every day, OCO-2 orbits Earth 14.5 times and returns about a million measurements. After eliminating data contaminated by clouds, aerosols, and steep terrain, between 10 to 13 percent of the measurements are of sufficient quality to derive accurate estimates of average carbon dioxide concentrations. That's at least 100 times more carbon dioxide measurements than from all other sources combined.
“The new, exciting thing from my perspective is that we have more than 100,000 measurements each day of carbon dioxide in the atmosphere,” said Annmarie Eldering, OCO-2 deputy project scientist, based at NASA’s Jet Propulsion Laboratory. “Armed with this pile of data, we can start to investigate more fully this question of sources and sinks and how different parts of the world contribute to these processes.”
Carbon naturally cycles through earthly environments. Ocean water naturally absorbs carbon dioxide from the atmosphere, and floating, microscopic phytoplankton soak it up as well. Trees, crops, and other plants on land take up carbon dioxide and turn it into the building blocks of roots, stems, branches, and leaves. Some of that carbon stays in the soil as vegetation dies and gets buried, and some is released back into the atmosphere through plant respiration. Both carbon dioxide and methane also are released through the decomposition of vegetation, land clearing, and fire. Over many millennia, the pace of carbon cycling is even influenced by volcanic emissions and the weathering of rocks.
For most of human history, this rhythmic exchange of carbon has been more-or-less steady. But the cycle has been thrown off in the past few centuries as ever-growing human populations have burned fossil fuels, cleared forests, and tilled soils for agriculture.
Today, about half of the carbon dioxide released by human activities stays in the atmosphere, warming and altering Earth’s climate. The other half is removed from the air by the plants, plankton, and oceans. “The huge question is: in the future, as the carbon dioxide builds up, will the land and the ocean continue to take up that 50 percent?” said Eldering. “Do they get saturated or full, and they quit at some point, or do they always just take up more and more and more?”
NASA Earth Observatory maps by Joshua Stevens, using data from the OCO-2 science team at NASA-JPL and Caltech. Caption by Mike Carlowicz, based on reporting by Alan Buis (JPL) and Kate Ramsayer and Carol Rasmussen (NASA Earth Science News Team). .