Enhanced land–sea warming contrast elevates aerosol pollution in a warmer world

Abstract

Many climate models simulate an increase in anthropogenic aerosol species in response to warming1, particularly over the Northern Hemisphere mid-latitudes during June, July and August. Recently, it has been argued that this increase in anthropogenic aerosols can be linked to a decrease in wet removal associated with reduced precipitation2, but the mechanisms remain uncertain. Here, using a state-of-the-art climate model (the Community Atmosphere Model version 5), we expand on this notion to demonstrate that the enhanced aerosol burden and hydrological changes are related to a robust climate change phenomenon—the land–sea warming contrast3,4. Enhanced land warming is associated with continental reductions in lower-tropospheric humidity that drive decreases in low clouds—particularly large scale (stratus) clouds—which, in turn, lead to reduced large-scale precipitation and aerosol wet removal. Idealized model simulations further show that muting the land–sea warming contrast weakens these hydrological changes, thereby suppressing the aerosol increase. Moreover, idealized simulations that only feature land warming yield enhanced continental aridity and an increase in aerosol burden. Thus, unless anthropogenic emission reductions occur, our results add confidence that a warmer world will be associated with enhanced aerosol pollution.

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Fig. 1: CAM5 seasonal and annual mean aerosol burden and wet deposition response to climate change.
Fig. 2: CAM5 seasonal mean hydrology response for default warming and muted land warming simulations.
Fig. 3: CAM5 seasonal mean response of aerosol burden and wet deposition due to LSP for default warming and muted land warming simulations.
Fig. 4: CAM5 seasonal mean response of aerosol burden and wet deposition due to LSP for enhanced land warming simulations.

Code availability

The codes used to process the CAM5 simulations are available from R.J.A.

Data availability

CAM5 data and simulations are available from R.J.A.

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Acknowledgements

T.H. is supported in part by the Fellowships and Internships in Extremely Large Data Sets programme, which is funded by the NASA MUREP Institutional Research Opportunity and developed by the University of California, Riverside and NASA’s Jet Propulsion Laboratory. R.J.A., T.H. and C.A.R. also acknowledge support from the ExxonMobil Research and Engineering Company. H.S. is supported by the NASA ACMAP programme, and conducted the work at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

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R.J.A. conceived the project, designed the study and performed the CAM5 simulations. R.J.A. and T.H. led the writing of the paper. T.H. carried out the data analysis and figure construction. C.A.R. and H.S. advised on interpretation of the results. All authors discussed the results and commented on the manuscript.

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Correspondence to Robert J. Allen.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Discussion, Supplementary Table 1, Supplementary Figures 1–11

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Allen, R.J., Hassan, T., Randles, C.A. et al. Enhanced land–sea warming contrast elevates aerosol pollution in a warmer world. Nat. Clim. Chang. 9, 300–305 (2019). https://doi.org/10.1038/s41558-019-0401-4

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