The OCO-2 Project science objectives are to collect the space-based measurements needed to quantify variations in the column averaged atmospheric carbon dioxide (CO2) dry air mole fraction, XCO2, with the precision, resolution, and coverage needed to improve our understanding of surface CO2 sources and sinks (fluxes) on regional scales (≥1000km) and the processes controlling their variability over the seasonal cycle. This mission validates a space-based measurement approach and analysis concept that could be used for future systematic CO2 monitoring missions.
What does this all mean? Carbon Dioxide or CO2 is one of the primary greenhouse gases on Earth. Greenhouse gases are those which can trap thermal radiation or heat that the Earth would otherwise emit to space.
CO2 is an important gas for life on the planet and integral to maintaining the protective blanket that is our atmosphere. However, sharp increases or decreases may affect the delicate atmospheric balance, and increases in atmospheric CO2 concentration may adversely alter the global climate. Although we know and understand the human activity impacts on CO2 concentrations in the atmosphere, several questions remain unanswered. Our ability to answer those questions will provide a more complete understanding that those impacts have and will have on the global climate.
The Earth system maintains a check and balance on CO2 through the carbon cycle and what we call sources and sinks. A source is any process where CO2 is released into the atmosphere such as plant and animal decay, deforestation, when we breathe out, or the burning of fossil fuels such as coal or gas. A sink is a reservoir that removes some of the CO2 from the atmosphere, such as when vegetation and trees take up CO2 for photosynthesis. The oceans remove some of the CO2 from the atmosphere as well.
The nature and the locations of the sinks that absorb about half of the human produced CO2 are currently not well known and present important, yet unanswered questions. For example, if the efficiency of these sinks decreases in the future, will the rate of buildup of atmospheric CO2 increase? If so, how much? Can some of these natural sinks be exploited to further reduce the rate of CO2 buildup? By better understanding the nature, locations, and processes that make these natural sinks, we can better predict the rate of buildup of CO2 in the atmosphere and its impact on our climate.
Today, fossil fuel combustion and other human activities are currently contributing about 39 billion tons or 39 Gigatons of CO2 into the atmosphere each year. So for each ton of carbon that is put in, we get 3.7 tons of CO2. This is only a small fraction (4%) of the 770 Gigatons of CO2 emitted into the atmosphere each year by natural processes in the ocean and on land. However, unlike the human activities, which only emit CO2 into the atmosphere, these same natural processes absorb as well as emit CO2. In fact, atmospheric CO2 measurements collected by a global network of surface stations indicate that these natural CO22 "sinks” not only absorb almost all of the CO2 emitted by natural processes, they also absorb almost half of the CO2 that is being emitted by human activities as well.
The concentration of CO2 in the atmosphere is measured in “parts per million by volume” (ppmv). For example, in 1970, atmospheric measurements indicated that about 330 out of every million air molecules was a CO2 molecule, yielding a concentration of 330 ppmv. Over the past 40 years, human emissions have increased the CO2 concentration by 1 to 2 ppmv per year, such that by 2013, the atmospheric CO2 concentration had increased by over 25% to values at or near 400 ppmv. At this rate and over a sufficient period of time, this efficient greenhouse gas will impact the Earth's climate.
OCO-2 measurements provides the global coverage, spatial resolution, and accuracy to provide a basis to characterize and monitor the geographic distribution of CO2 sources and sinks and quantify their variability. Based on these measurements, scientists map the natural and man-made processes that regulate the exchange of CO2 between the Earth's surface and the atmosphere on both regional to continental scales. These measurements allow more reliable forecasts of the atmospheric CO2 abundance and its impact on the Earth's climate.
The OCO-2 mission contributes to a large number of additional scientific investigations that are related to the global carbon cycle. Among these studies are: