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Global Radiative Impacts of Black Carbon Acting as Ice Nucleating Particles
Zachary McGraw1, Trude Storelvmo1, Bjørn Hallvard Samset2
1Department of Geosciences University of Oslo Oslo Norway.
Geophysical Research Letters
|December 31, 2020
Summary
Black carbon (BC) aerosols act as ice nucleating particles (INPs), causing a cooling effect by thinning clouds. This finding partially offsets BC
Area of Science:
- Atmospheric Science
- Climate Science
- Aerosol Science
Background:
- Black carbon (BC) aerosols from incomplete combustion are known climate warmers.
- The role of BC as ice nucleating particles (INPs) in cloud formation remains a significant knowledge gap.
- Understanding BC's interactions with clouds is crucial for accurate climate modeling.
Purpose of the Study:
- To assess the global radiative impacts of black carbon acting as INPs.
- To quantify the net radiative effect of BC-mediated ice nucleation in clouds.
- To investigate the influence of BC INPs on cloud properties and radiative balance.
Main Methods:
- Utilized the Community Earth System Model 2 (CESM2) for climate simulations.
- Incorporated new laboratory-based ice nucleation parameterizations for BC.
- Performed sensitivity tests on BC concentrations and ice nucleating efficiencies.
Main Results:
- BC acting as INPs induces a moderate cooling effect, primarily through thinning of stratiform cirrus clouds.
- This cooling effect (-0.13 ± 0.07 W/m²) partially counteracts the warming from BC's direct radiative effects.
- BC INPs were found to inhibit the freezing of solution aerosols, leading to cirrus cloud thinning.
Conclusions:
- Black carbon's role as INPs introduces a cooling influence on the climate, contrary to its direct warming effect.
- The net radiative impact of BC INPs is estimated to be between -0.30 and +0.02 W/m².
- Accurate representation of BC as INPs is essential for refining climate projections.
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