Increased Global Land Carbon Sink Due to Aerosol‐Induced Cooling

Abstract

Anthropogenic aerosols have contributed to historical climate change through their interactions with radiation and clouds. In turn, climate change due to aerosols has impacted the C cycle. Here we use a set of offline simulations made with the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model driven by bias‐corrected climate fields from simulations of three Coupled Model Intercomparison Project Phase 5 (CMIP5) Earth system models (ESMs; IPSL‐CM5A‐LR, CSIRO‐Mk3.6.0, and GISS‐E2‐R) to quantify the climate‐related impacts of aerosols on land carbon fluxes during 1860–2005. We found that climate change from anthropogenic aerosols (CCAA) globally cooled the climate, and increased land carbon storage, or cumulative net biome production (NBP), by 11.6–41.8 PgC between 1860 and 2005. The increase in NBP from CCAA mainly occurs in the tropics and northern midlatitudes, primarily due to aerosol‐induced cooling. At high latitudes, cooling caused stronger decrease in gross primary production (GPP) than in total ecosystem respiration (TER), leading to lower NBP. At midlatitudes, cooling‐induced decrease in TER is stronger than that of GPP, resulting in NBP increase. At low latitudes, NBP was also enhanced due to the cooling‐induced GPP increase, but precipitation decline from CCAA may negate the effect of temperature. The three ESMs show large divergence in low‐latitude CCAA precipitation response to aerosols, which results in considerable uncertainties in regional estimations of CCAA effects on carbon fluxes. Our results suggest that better understanding and simulation of how anthropogenic aerosols affect precipitation in ESMs is required for a more accurate attribution of aerosol effects on the terrestrial carbon cycle.

The DOE E3SM v1.1 Biogeochemistry Configuration: Description and Simulated Ecosystem‐Climate Responses to Historical Changes in Forcing

“…The slightly positive average values of NEE until the midtwentieth century reflect the net effects of a carbon source associated with LULCC, which exceeded the magnitude of the net carbon sink associated with CO 2 and nitrogen deposition fertilization of plant growth, consistent with observational estimates (Le Quéré et al, 2018). Aerosol‐induced cooling may also act to reduce the land carbon sink during the historical period (Zhang et al, 2019), but we are unable to disentangle this effect from CO 2 effects in the simulations. In the late twentieth century, NEE becomes negative in BD simulations, as the land responds to increasing atmospheric CO 2 concentrations by increasing its uptake of CO 2 .…”

The response of terrestrial ecosystem carbon cycling under different aerosol-based radiation management geoengineering

“…Due to the long thermal inertia in the climate system and limitations on the maximum removal rate of CO 2 , CDR would likely require more time to lower global temperatures (Zickfeld et al, 2017) compared to RM methods. On the other hand, several proposed RM methods could stabilize or even reduce global temperature within a few years (Lawrence et al, 2018).…”

Modeling the impacts of diffuse light fraction on photosynthesis in ORCHIDEE (v5453) land surface model

“…These parameterizations calculate photosynthesis per unit LAI considering the stress from temperature, VPD and soil water, and then integrate it over the entire canopy volume. Therefore, the effects of temperature and VPD change under cloudier conditions have usually been implicitly considered in current LSMs (e.g., Zhang et al, 2019). However, for the sake of simplicity and computational efficiency and due to the lack of diffuse light fraction data, most global LSMs have assumed a single extinction coefficient for both direct and diffuse light (Sellers et al, 1997;Sitch et al, 2008).…”