labs_title

Characterizing biospheric carbon balance using CO2 observations from the OCO-2 satellite

S.M. Miller, A.M. Michalak, V. Yadav and J.M. Tadić

The Orbiting Carbon Observatory 2 (OCO-2) is NASA’s first satellite dedicated to monitoring carbon dioxide (CO2) from space. Space-based CO2 measurements are a relatively new but rapidly growing field, and both NASA and foreign space agencies are planning several new instruments to launch in coming years. This study explores a first step toward the goal of observing the biospheric carbon balance from space; we evaluate the extent to which current OCO-2 observations can be used to robustly estimate this carbon balance around the global. We find that current observations are best able to constrain the carbon balance across large continents or hemispheres and that current observations have limited ability to inform CO2 estimates across smaller regions. In spite of these current limitations, OCO-2 observations show great potential. Specifically, our results indicate that errors in current observations have a salient effect on the results, and ongoing efforts to improve data processing could dramatically improve the capabilities of OCO-2 data.


Figure: We divide the world into different regions and explore whether current OCO-2 observations can detect patterns in CO2 sources and sinks within each region. Detection is a pre-requisite for estimating the carbon balance using OCO-2 observations. Dark blue colors indicate that the observations do an excellent job of detecting CO2 sources and sinks while light colors indicate poor ability. We run three different experiments. In the first experiment, we divide the world into two regions and explore whether we can detect patterns in CO2 sources and sinks from those regions. In subsequent experiments (panels b and c), we divide the globe into smaller regions, a more stringent test of the OCO-2 data. Overall, we often able to detect CO2 sources in sinks across large hemispheres but are rarely able to detect patterns in CO2 sources in sinks within smaller biome-based regions.

Abstract

NASA's Orbiting Carbon Observatory 2 (OCO-2) satellite launched in summer of 2014. Its observations could allow scientists to constrain CO2 fluxes across regions or continents that were previously difficult to monitor. This study explores an initial step toward that goal; we evaluate the extent to which current OCO-2 observations can detect patterns in biospheric CO2 fluxes and constrain monthly CO2 budgets. Our goal is to guide top-down, inverse modeling studies and identify areas for future improvement. We find that uncertainties and biases in the individual OCO-2 observations are comparable to the atmospheric signal from biospheric fluxes, particularly during northern hemisphere winter when biospheric fluxes are small. A series of top-down experiments indicate how these errors affect our ability to constrain monthly biospheric CO2 budgets. We are able to constrain budgets for between two and four global regions using OCO-2 observations, depending on the month, and we can constrain CO2 budgets at the regional level (i.e., smaller than seven global biomes) in only a handful of cases (16% of all regions and months). The potential of the OCO-2 observations, however, is greater than these results might imply. A set of synthetic data experiments suggests that retrieval errors have a salient effect. Advances in retrieval algorithms and to a lesser extent atmospheric transport modeling will improve the results. In the interim, top-down studies that use current satellite observations are best-equipped to constrain the biospheric carbon balance across only continental or hemispheric regions.

Miller, S.M., A.M. Michalak , V. Yadav, J.M. Tadić (2018) "Characterizing biospheric carbon balance using CO2 observations from the OCO-2 satellite," Atmospheric Chemistry and Physics, 18 (9), 6785-6799, doi:10.5194/acp-18-6785-2018.