Detecting Carbon-Climate Feedbacks from Leaf to Globe
Abstract:The Grand Challenge of Carbon Cycle Science is to understand how carbon exchange between the land and atmosphere will evolve under future climate change and how this will impact atmospheric CO2 concentrations. In particular, large pools of carbon stored in soils and in biomass have potential to be released to the atmosphere and accelerate climate feedbacks. Reducing uncertainties in carbon cycle projections requires methods to constrain overall rates of photosynthetic C uptake at planetary scale and detect feedback processes, especially in tropical and Arctic regions where feedbacks are likely to be largest but where observations are the fewest. Measurements of solar induced chlorophyll fluorescence (SIF) from plants, representing a direct outcome of foliar light absorption by chlorophyll modified by biochemical feedbacks, provide an important new proxy for photosynthesis. The combination of recently available satellite-derived SIF and atmospheric CO2 has provided key insight on carbon cycle dynamics and have improved quantification of CO2 balance at planetary, regional, and grid scale. However, many factors affecting leaf-to-canopy extrapolation remain poorly constrained, and therefore limit the power of joint spaceborne SIF and CO2 systems to develop mechanistic and quantitative understanding of photosynthetic carbon uptake. Airborne and field-deployable SIF spectrometers can help refine our understanding of SIF-photosynthesis relationships at leaf, canopy, and ecosystem scales, thereby maximizing the quantitative and predictive power of the growing number of existing (GOSAT, GOME-2, OCO-2) and planned (OCO-3, TROPOMI, GeoCARB) satellite SIF observing systems for broader integrated analysis. Here, I will summarize current progress in SIF remote sensing in tropical and Arctic regions, and discuss plans moving forward for more sophisticated synthesis of satellite, airborne, and tower data.