Orbiting Carbon Observatory 2, or OCO-2. Image created by John Howard/JPL.
Humans have long participated in the planet’s carbon cycle through respiration, but in recent centuries, our impact has grown significantly. Activities like fossil fuel combustion and deforestation have disrupted the cycle’s natural equilibrium, resulting in a steady increase in atmospheric carbon dioxide levels. While land and oceans will absorb most carbon over time, up to 20% may linger in the atmosphere for millennia. Excess atmospheric carbon warms the planet, while excess carbon in the ocean leads to acidification, threatening marine ecosystems. There remains significant uncertainty regarding the specifics of these processes, such as their location and how they may be influenced by warming temperatures. To effectively comprehend and adapt to the evolving carbon cycle, it is necessary that we prioritize research efforts to fill these knowledge gaps.
NASA plays a vital role in addressing these questions by leveraging global satellite observations and associated field research. The Orbiting Carbon Observatory (OCO) is a pioneering spacecraft dedicated to studying atmospheric carbon dioxide. Its mission aims to enhance our understanding of the carbon cycle and the mechanisms governing atmospheric CO₂ levels. Despite the setback of the original spacecraft’s loss in a launch failure in 2009, the subsequent launch of its replacement, Orbiting Carbon Observatory-2 (OCO-2), in 2014 marked a significant milestone. Additionally, Orbiting Carbon Observatory-3 (OCO-3), utilizing spare components from OCO-2, was deployed on the International Space Station in 2019, furthering NASA’s efforts in carbon observation and climate research.
OCO-2 and OCO-3 are equipped with advanced spectrometers capable of precisely measuring the concentration of carbon dioxide in Earth’s atmosphere. These spectrometers are specifically engineered to detect the distinct spectral “fingerprints” of various atmospheric gases. As sunlight traverses Earth’s atmosphere and reflects off its surface, molecules of atmospheric gases selectively absorb certain colors of light. When this light spectrum is dispersed into a rainbow of colors, each gas leaves behind dark absorption lines at specific wavelengths, creating a unique pattern for that molecule. The amount of light absorbed within each spectral line corresponds to the concentration of molecules along the optical path. OCO’s spectrometers are finely tuned to capture these molecular fingerprints, enabling precise measurements of carbon dioxide and molecular oxygen absorption in the near-infrared spectrum. By analyzing these absorption patterns, scientists can accurately quantify carbon dioxide concentrations in the atmosphere, providing invaluable data for understanding the carbon cycle and its role in climate change.
CO₂ concentrations in the atmosphere are typically measured in parts per million (ppm), indicating the number of carbon dioxide molecules present per million molecules of air. Currently, this concentration is around 400 ppm. The spectrometers aboard OCO-2 and OCO-3 can detect changes as small as one or two molecules within the 400-ppm range. OCO-2 gathers an impressive 24 measurements per second over the sunlit portion of Earth’s hemisphere, amounting to over a million measurements daily. These measurements serve as crucial input for global atmospheric models. When combined with data on atmospheric conditions like wind patterns, they enable modelers to pinpoint carbon sources and sinks at regional scales, down to areas comparable in size to France or Texas.
Atmospheric CO2 concentration observed by OCO-2 satellite.
OCO-3 continues the CO2 monitoring initiated by its predecessor, OCO-2. While OCO-2 operates in a near-polar orbit, ensuring it passes over the same point on Earth’s surface at the same time each day, OCO-3’s location on the space station presents a notable difference. The space station completes approximately 16 orbits of Earth daily, with each orbit shifting slightly to the west due to Earth’s rotation. Consequently, OCO-3 has the advantage of measuring CO2 levels over the same regions at varying times of day. This capability enhances our understanding of diurnal CO2 variations, offering valuable insights into the dynamics of the carbon cycle and its interaction with daily atmospheric processes.
In addition to the OCO missions, various worldwide projects, including ocean and land in-situ sensors, contribute to increasing spatial resolution. These measurements aid in tracking changes in the global carbon cycle over time, gauging human impact on carbon release and storage. They highlight how climate change affects the carbon cycle and vice versa.
