Exploring the environmental drivers of global terrestrial CO2 fluxes
inferred from OCO-2 and a geostatistical inverse model
Abstract
The carbon cycle displays strong sensitivity to short term variations in
environmental conditions, and it is key to understand how these
variations are linked with variations in CO2 fluxes. Previously,
atmospheric observations of CO2 have been sparse in many regions of the
globe, making it challenging to evaluate these relationships. However,
the OCO-2 satellite, launched in July 2014, provides new insight into
global CO2 fluxes, particularly in regions that were previously
difficult to monitor. In this study, we combine OCO-2 observations with
a geostatistical inverse model to explore data-driven relationships
between inferred CO2 flux patterns and environmental drivers. We further
use year 2016 as an initial case study to explore the applicability of
the geostatistical approach to large satellite-based inverse problems.
We estimate daily, global CO2 fluxes at the model grid scale and find
that a combination of air temperature, daily precipitation, and
photosynthetically active radiation (PAR) best describe patterns in CO2
fluxes in most biomes across the globe. PAR is an adept predictor of
fluxes across mid-to-high latitudes, whereas a combined set of daily air
temperature and precipitation shows strong explanatory power across
tropical biomes. However, we are unable to quantify a larger number of
relationships between environmental drivers and CO2 fluxes using OCO-2
due to the limited sensitivity of total column satellite observations to
detailed surface processes. Overall, we estimate a global net biospheric
flux of -1.73 ± 0.53 GtC in year 2016, in close agreement with recent
inverse modeling studies using OCO-2 retrievals as observational
constraints.