Science

CO₂ is an efficient greenhouse gas. Increases in the concentration of atmospheric CO₂ may adversely alter the global climate. Although a good deal 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. Natural sources of CO₂ emit approximately 300 Gigatons of CO₂ each year. Human activities are responsible for about 6 Gigatons, or a mere 2% of that total. Measurements from a global network of surface stations over the past 40 years indicate an average annual increase of CO₂ in the atmosphere of about 1%. A 1% annual increase in CO₂ concentration seems small. Over a sufficient period of time, however, this rate of increase may generate an imbalance in the global carbon cycle. Such an imbalance could seriously exacerbate climate change. Using these measurements, researchers conclude that the biosphere and oceans are absorbing almost half of the carbon that has been emitted into the atmosphere. The nature and the geographic distribution of the sinks that absorb half of the human generated CO₂ present important, yet unanswered questions. If the efficiency of these sinks decreases in the future, the buildup of atmospheric CO₂ could accelerate. The ability to predict the location and the efficiency of CO₂ sinks depends upon an enhanced understanding of the processes that govern the abundance of CO₂ in the atmosphere.

The global coverage, spatial resolution, and accuracy of OCO 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 and continental scales. Further improvements in the understanding of these processes will enable more reliable forecasts in the measure of atmospheric CO₂ column abundance and the impact of these changes on the Earth's climate.

The OCO mission will contribute to a large number of additional scientific investigations that are related to the global carbon cycle. Among these studies are:

• the dynamics of ocean carbon exchange
• the seasonal dynamics of northern hemisphere terrestrial ecosystems in Eurasia and North America
• the exchange of carbon between the atmosphere and tropical ecosystems due to plant growth, respiration, and fires
• the movement of fossil fuel plumes across North America, Europe, and Asia
• the effect of weather fronts, storms, and hurricanes on the exchange of CO₂ between different geographic and ecological regions
• the mixing of atmospheric gases across hemispheres