CO2 is an efficient greenhouse gas, which can trap thermal (heat) radiation that the Earth would otherwise emit to space. Increases in atmospheric CO2 concentration may adversely alter the global climate. Although much is known about the impact of human activity on the concentration of CO2 in the atmosphere, several questions remain unanswered. Our ability to answer those questions may very well provide a more complete understanding of the impact that human activity currently has and will have on the global climate.
Fossil fuel combustion and other human activities are currently emitting about 30 billion tons or 30 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 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 CO2 “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 2011, the atmospheric CO2 concentration had increased by over 18% to values over 390 ppmv. If these CO2 increases continue over a sufficient period of time, this efficient greenhouse gas could reduce the Earth’s ability to thermal radiation to space, altering its climate.
Larger View of Carbon Cycle (JPG, 175 KB)
The nature and the geographic distribution of the sinks that absorb about half of the human generated 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? An improved understanding of nature, location, and processes governing the efficiency of these natural sinks is therefore essential to predict the rate of buildup of CO2 in the atmosphere, and its impact on our climate.
The global coverage, spatial resolution, and accuracy of OCO-2 measurements will provide a basis to characterize and monitor the geographic distribution of CO2 sources and sinks and quantify their variability. Based on these measurements, scientists will 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 will enable more reliable forecasts of the atmospheric CO2 abundance and its impact on the Earth's climate.
The OCO-2 mission will contribute to a large number of additional scientific investigations that are related to the global carbon cycle. Among these studies are: