Observing carbon cycle–climate feedbacks from space

Abstract

The impact of human emissions of carbon dioxide and methane on climate is an accepted central concern for current society. It is increasingly evident that atmospheric concentrations of carbon dioxide and methane are not simply a function of emissions but that there are myriad feedbacks forced by changes in climate that affect atmospheric concentrations. If these feedbacks change with changing climate, which is likely, then the effect of the human enterprise on climate will change. Quantifying, understanding, and articulating the feedbacks within the carbon-climate system at the process level are crucial if we are to employ Earth system models to inform effective mitigation regimes that would lead to a stable climate. Recent advances using space-based, more highly resolved measurements of carbon exchange and its component processes-photosynthesis, respiration, and biomass burning-suggest that remote sensing can add key spatial and process resolution to the existing in situ systems needed to provide enhanced understanding and advancements in Earth system models. Information about emissions and feedbacks from a long-term carbon-climate observing system is essential to better stewardship of the planet.

Flux towers in the sky: global ecology from space

“…Quantifying the direct release of carbon from land use change and deforestation has been a long‐term goal of global ecologists (Houghton et al ., ), but precise estimates have long remained elusive, and trends (decreases or increases) have been difficult to determine with confidence. Combining the top‐down measurement of carbon budgets from space (Liu et al ., ; Sellers et al ., ) with biomass estimates constrained by LiDAR and radar holds great promise for determining the impacts of deforestation and degradation on continental or subcontinental scales (Bustamante et al ., ). But besides the direct human impact on the carbon budget, such as through deforestation and biomass burning, there are also indirect effects, for example through forest fragmentation (Brinck et al ., ) and biodiversity loss (Isbell et al ., ).…”

“…Using space‐based observations, we can close the carbon budget but quite differently than with eddy covariance, estimating R eco as the residual of NECB from , GPP from SIF and including an additional disturbance component, fire emissions estimated from atmospheric CO (Liu et al ., ; Sellers et al ., ): …”

“…GPP is estimated from SIF using the Berry equation (Sellers et al ., ): where this ε is the amount of photosynthesis per unit SIF emitted, or the SIF efficiency (Sellers et al ., ). While ε is a variable at the molecule and leaf level, it appears surprisingly invariant globally when SIF is measured vs GPP at flux sites, combining the surface network with remote sensing (Sun et al ., ), except perhaps under extreme stress (Verma et al ., ).…”

“…Global gross and net primary productivity (GPP and NPP) and how these are changing with climate and human land use are critical for understanding the Earth as a biogeophysical system, for understanding carbon cycleÀclimate feedback, and for defining limits to sustainability (Vitousek et al, 1986;Running, 2012;Sellers et al, 2018). New remote sensing methodologies provide new constraints on GPP (Frankenberg et al, 2011) and biomass observations over time from radar and LiDAR provide a direct measure of aboveground biomass accumulation and loss (Fatoyinbo et al, 2017).…”

“…Satellite measurements are increasingly central to understanding trends in the biosphere as a whole, and as described above, now characterise a far wider range of ecosystem properties than just greenness. Today, researchers can begin to see patterns of actual carbon exchange, storage and key controls emerging on seasonal to short interannual times scales , setting the stage for quantification and explanations of change (Sellers et al, 2018).…”