Monitoring Carbon Dioxide and Photosynthesis from Space
The OCO constellation provides spaceborne measurements of atmospheric carbon dioxide (CO2) and solar-induced chlorophyll fluorescence (SIF), a proxy for plant photosynthetic activity. Together, the SIF and CO2 data illustrate the key role that the terrestrial biosphere plays in controlling the variation of atmospheric CO2. The growing length of the OCO record enables study of how temperature, draught, and events such as El Niño change the biosphere and its impact on CO2. OCO-2 began operations in 2014 and was joined by OCO-3 in 2019 (observing from the International Space Station)
Data from the 12 year record of OCO are shown in this visualization:
Upper left: The mixing ratio of carbon dioxide averaged between the surface and space (XCO2). A linear increase in XCO2 has been subtracted so the visualization highlights the variation of CO2 in each year. There is no data at high latitude during winter because OCO uses measurements of reflected sunlight to quantify CO2. In the tropics, it is rarely possible to measure XCO2 during the rainy season because the presence of clouds obscures the ability to quantify the small variations in XCO2 (~1-2% globally).
Upper right: The signal from the fluorescence of plants (Solar Induced chlorophyll Fluorescence (SIF)). In forested and agricultural regions, SIF 'lights up' as sunlight returns and temperatures warm in spring. In the tropics, the SIF varies with sunlight and the amount of rainfall.
Bottom: The green line shows global SIF - peaking in northern hemisphere summer. In yellow the time rate of change of global XCO2 is shown. In the Northern Hemisphere, CO2 declines dramatically following the beginning of spring as plants inhale carbon dioxide to build biomass. During fall, respiration from metabolism in plants and soils exceeds photosynthesis returning CO2 back to the atmosphere which, together with fossil CO2 emissions, leads to the substantial increase in XCO2 over the winter months until spring returns again. Since the launch of OCO-2, atmospheric CO2 has increased by 25 ppm (blue line) as a result of the burning of fossil fuels. The increase would have been twice as large if the oceans and the terrestrial biosphere hadn't sequestered half of these emissions.
