Causes of Decelerating Seasonal CO2 Amplitude at Mauna Loa
Abstract
The changing amplitude of the seasonal cycle of atmospheric CO2 (SCA) in the northern hemisphere is an emerging property of the carbon cycle and there is a general consensus that, since the 1980s, SCA has significantly increased at high latitude stations, but not at lower latitude stations (e.g. Mauna Loa (MLO))1,2. However, the MLO station, which has the longest continuous northern hemisphere CO2 record, and integrates CO2 mostly from the temperate northern hemisphere, shows an increasing amplitude before the 1980s (P < 0.01), followed by no significant change thereafter. This intriguing deceleration in the CO2 amplitude change after the 1980s has attracted less attention than the persistent increase at higher latitudes sites such as Point Barrow (BRW). We analyzed the potential driving factors (terrestrial and ocean carbon fluxes, land use emissions, fossil fuel emissions and atmospheric circulation) of the change in the SCA trend, with an ensemble of dynamic global vegetation models (DGVMs) coupled with an atmospheric transport model. As only a subset of the DGVMs reproduced the observed SCA changes, we used Bayesian model averaging (BMA) to construct a skill-based weighted ensemble to estimate the contribution from each factor. We found that the slow-down of SCA trend at MLO is primarily explained by the response of net biome productivity (NBP) to climate change, and by changes in atmospheric circulation. Through NBP, climate change increases SCA at MLO before the 1980s and decreases it afterwards probably due to intensified drought stress, with the latter acting to offset the acceleration driven by CO2 fertilization. This result challenges the view that the effect of CO2 fertilization in northern ecosystems is the dominant cause of emergent trends in SCA, at least for the temperate northern hemisphere influencing the MLO record.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B13H2591W
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0480 Remote sensing;
- BIOGEOSCIENCES