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Abstract The ocean’s major circulation system, the Atlantic Meridional Overturning Circulation (AMOC), is slowing down. Such weakening is consistent with warming associated with increasing greenhouse gases, as well as with recent decreases in industrial aerosol pollution. The impact of biomass burning aerosols on the AMOC, however, remains unexplored. Here, we use the Community Earth System Model version 1 Large Ensemble to quantify the impact of both aerosol types on the AMOC. Despite relatively small changes in North Atlantic biomass burning aerosols, significant AMOC evolution occurs, including weakening from 1920 to ~1970 followed by AMOC strengthening. These changes are largely out of phase relative to the corresponding AMOC evolution under industrial aerosols. AMOC responses are initiated by thermal changes in sea surface density flux due to altered shortwave radiation. An additional dynamical mechanism involving the North Atlantic sea-level pressure gradient is important under biomass-burning aerosols. AMOC-induced ocean salinity flux convergence acts as a positive feedback. Our results show that biomass-burning aerosols reinforce early 20th-century AMOC weakening associated with greenhouse gases and also partially mute industrial aerosol impacts on the AMOC. Recent increases in wildfires suggest biomass-burning aerosols may be an important driver of future AMOC variability.
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This content will become publicly available on December 1, 2026
Distinct impacts of diverse forcing agents on Arctic sea ice since the mid-twentieth century
Abstract Arctic sea ice has undergone non-monotonic changes since the middle of the last century. Here, we investigate the cause of this behavior by isolating and quantifying the effects of anthropogenic aerosols, well-mixed greenhouse gases, and biomass burning on sea ice dynamics through climate model simulations. We find minimal changes in Arctic sea ice from 1956 to 1980, which largely reflect a balance between the warming effect of greenhouse gases and the cooling effect of aerosols. This balance, however, is disrupted in subsequent decades. Both sea ice area and volume exhibit marked declines between 1981 and 2005, owing primarily to intensified warming by greenhouse gases and a shift in aerosols’ role from mitigating to exacerbating sea ice loss. Our sea ice volume budget analysis demonstrates that sea ice changes since 1956 are mostly driven by thermodynamic processes: greenhouse gases significantly promote surface melting, whereas aerosols and biomass burning diminish surface melting by reducing surface shortwave radiation during boreal summer. From 1956–1980 to 1981–2005, the transitional effects of aerosols are associated with increased bottom ice melting and decreased bottom ice formation, which are primarily driven by changes in the Atlantic meridional overturning circulation.
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- PAR ID:
- 10677632
- Publisher / Repository:
- Springer Nature
- Date Published:
- Journal Name:
- npj Climate and Atmospheric Science
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2397-3722
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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