Large-scale observational and modelling-based constraints of the CO2 fertilization effect
Abstract
Increasing atmospheric CO2 concentration is expected to enhance photosynthesis and water-use efficiency and enhance the global land CO2 uptake in the absence of limitations or disturbances. The existence of a persistent and increasing sink in the terrestrial biosphere since the beginning of the observational record is supported by several lines of evidence. Most of this sink is located in the northern hemisphere, since in the tropics the increase in CO2 uptake is offset by strong emissions from land-use change. Quantifying to which extent the enhancement of the land sink is controlled by the CO2 fertilization effect or by other factors, such as temperature, however, remains a challenge.
The attribution of the land-sink enhancement to the CO2 fertilization effect requires accurate partitioning of the net land-atmosphere CO2 fluxes into natural and anthropogenic sinks and sources, as well as the quantification of the impacts of nutrient limitations and climate-change on those fluxes. In spite of good agreement at the global scale, top-down estimates (atmospheric inversions) of the net land sink still show large uncertainties in the sink partitioning between the northern hemisphere and the tropics. In this presentation, we revisit the recent progress on large-scale constraints of the global land sink and of the CO2 fertilization effect. We evaluate to which extent we can constrain the global and regional CO2 fluxes and the sensitivity of the terrestrial sink to atmospheric CO2 from top-down and bottom-up estimates. Compared to atmospheric inversions, process-based models underestimate the increase in the land global land sink, but in the northern high latitudes process-based models estimate an increasing trend within the uncertainty of inversions. We further analyze sources of uncertainty in these estimates and discuss potential reasons for disagreement between observation-based and process-based modelling estimates.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B11B..01B
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 1630 Impacts of global change;
- GLOBAL CHANGE