Contribution of Black Carbon Aerosol to Drying of the Mediterranean Tao Tang & Drew Shindell PDRMIP meeting 05-11-2017

MOTIVATIONS 1. Mediterranean has been drying since the mid-20th century 2. Previous studies included all the drivers at once. 3. Aerosol has been reported to affect Mediterranean temperature, but its role in precipitation has not been carefully examined.

DATA & METHODS Time period: 1951-2010 wet season (boreal winter) 9 Models: CanESM2, GISS-E2, HadGEM2, HadGEM3, NCAR-CAM4, NCAR-CAM5, NorESM, MIROC, IPSL-CM5A

DATA & METHODS BCX10 Observed Control run △P = 3 mm/d ERF = 2 W/m2 △Pscaled = △Pmodel × (ERFhist / ERFmodel) = 3 mm/d × = 1.5 mm/d 2 W/m2

DATA & METHODS Linearity

DATA & METHODS Climate forcing Forcing Agent ERFhist (W/m2) WMGHGs 1.89 BC 0.24 SO4 -0.22 Natural -0.13 Land use/cover change -0.05 Contrail 0.05 O3 0.2 Stratospheric H2O 0.03 0.1 (IPCC, 2013)

△Pscaled for (a) CO2, (b) BC, (c) SO4 and (d) combination, (e) GPCC, and (f) GHCN.

Domain-averaged △Pscaled (a) CO2, (b) BC, (c) SO4 and (d) combination

∆SLPscaled for (a) CO2, (b) BC, (c) SO4 and (d) combination

Domain-averaged vertical ∆Tscaled for (a) CO2, (b) BC, (c) SO4 and (d) combination

Scatter plot for domain-averaged ∆Pscaled (mm/decade) against the difference of ∆Tscaled between the upper atmosphere and the surface (K/decade)

Discussion & Limitations 1. Similar climate response to BC and WMGHGs 2. A drier Mediterranean in the future 3. No systematic studies on linearity 4. ERFhist of BC is direct effect only

Conclusions BC aerosol forcing contribute roughly 30% to the drying of Mediterranean. Due to further north displacement of storm tracks and jet streams. BC emissions have profound social-economic impacts.

Acknowledgements PDRMIP colleagues and their funding agency

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