Investigation of the U.S. warming hole and other adventures in chemistry-climate interactions Loretta J. Mickley Pattanun Achakulwisut, Becky Alexander, Tom Breider, Bryan Duncan, Rynda Hudman, Daniel Jacob, Jennifer Logan, Shannon Koplitz, Eric Leibensperger, Lee Murray, Justin Parrella, David Rind, Lulu Shen, Dominick Spracklen, Amos Tai, Shiliang Wu, Xu Yue, and Lei Zhu Running head for JAL’s first atmos chem paper wildfire in Southern California

2013 ~1:1 ratio in 50

Ozone PM 2.5 Millions of people in US living in areas in violation of the EPA standards. What is climate penalty on air quality? How will size of bars change with changing climate? How do trends in short-lived species affect global and regional climate? Regional forcings are as large as global forcings from well-mixed GHGs. Short-lived species can affect methane lifetime Calculated trend in surface sulfate concentrations Observations in circles -2 Wm -2 Leibensperger et al., 2012

Atmospheric Chemistry Assimilated meteorology GEOS-4 GEOS-5 GEOS-Chem Atmospheric Chemistry Land cover model GEOS-Chem Meteorology from freely running climate model Fire prediction model Chemical feedbacks Model frameworks 1. Standard 2. Chemistry-climate

1. Examine observed sensitivities of short-lived species or other variables to meteorology. E.g. Area burned = f(meteorology) 2. Apply sensitivities to archived meteorology from an ensemble of models. Some methods to overcome uncertainties in model apparatus. Yue et al., in review Area burned (10 5 ha) R 2 ~ 0.5 Area burned over Southwest model observed Area burned (10 5 ha) Timeseries of area burned observed model 3. Benchmark chemistry- climate interactions in the recent + distant past with observations. Arctic Last Glacial Maximum Equatorial Asia 2000s Area burned in Southwest US may double by 2050.

Observed US surface temperature trend GISTEMP 2010 Is the U.S. “warming hole” a signature of cooling due to anthropogenic aerosols? Observed spatial trend in temperatures, No trend between 1930 and Warming trend after 1980 Contiguous US 1 0 o C 1

We applied decadal trends in anthropogenic aerosol to the GISS climate model. Increasing sulfate from s. Decreasing sulfate beginning in 1990s Leibensperger et al., 2012a Calculated trend in surface sulfate concentrations Clearing trend in particles over United States since 1980s suggests possible recent warming. Circles show observations.

Leibensperger et al., 2012a. Direct radiative forcing Indirect radiative forcing Forcing from US anthropogenic aerosols peaks in s. Forcings over Eastern US Peak forcings -2 W m -2, mainly from sulfate. Warming from black carbon offsets the cooling early in the record. Results suggest little climate benefit to reducing black carbon sources in US.

C Leibensperger et al., 2012b Cooling from U.S. anthropogenic aerosols during Results are from two 5-member ensembles, with and without US anthropogenic aerosols. Cooling is greatest over the Eastern US and North Atlantic. 1 o C cooling at surface over East

 Model Temperature C  Soil moisture availability  Cloud Cover % Cooling over U.S. is not co-located with aerosol burden. Cooling over North Atlantic strengthens Bermuda High, increasing onshore flow of moisture from Gulf of Mexico. Local changes in cloud cover and soil moisture amplify the cooling effect. Results are controversial.

Inclusion of US anthropogenic aerosols improves match with observed trends in surface temperatures over the East. Most of the warming from reducing aerosol sources has already been realized. Results suggest that US anthropogenic aerosols can explain the “warming hole.” Warming since 1990s can be attributed to reductions in aerosol sources. Leibensperger et al., 2012b Observations Model without US aerosols Standard model Eastern US

U.S. BC emissions (Tg C) 1850 U.S. SO 2 emissions (Tg S) BC SO 2 Timeseries of US emissions How have competing trends in BC and SO 2 over 20th century affected regional climate across mid-latitudes? Ongoing work. BC aerosol warms mid- to upper troposphere cools surface stabilizes atmosphere SO 2 cools surface, may augment stabilization. We will compare model BC with lake core sediments from Adirondacks (Husain et al., 2008) BC deposition (g m-2 a-1) obst observations model Deposition in Adirondacks Leibensperger