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Investigation of the U.S. warming hole and other adventures in chemistry-climate interactions

Running head for JAL’s first atmos chem paper. Investigation of the U.S. warming hole and other adventures in chemistry-climate interactions. Loretta J. Mickley

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Investigation of the U.S. warming hole and other adventures in chemistry-climate interactions

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  1. Running head for JAL’s first atmoschem paper. Investigation of the U.S. warming hole and other adventures in chemistry-climate interactions Loretta J. Mickley PattanunAchakulwisut, Becky Alexander, Tom Breider, Bryan Duncan, RyndaHudman, Daniel Jacob, Jennifer Logan, Shannon Koplitz, Eric Leibensperger, Lee Murray, Justin Parrella, David Rind, Lulu Shen, DominickSpracklen, Amos Tai, ShiliangWu, XuYue, and Lei Zhu 2009 wildfire in Southern California

  2. 1977 1 in 50 2013 ~1:1 ratio

  3. What is climate penalty on air quality? How will size of bars change with changing climate? Ozone PM2.5 Millions of people in US living in areas in violation of the EPA standards. 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 -2 Wm-2 Observations in circles 1990 2001 Leibensperger et al., 2012

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

  5. Some methods to overcome uncertainties in model apparatus. 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. Area burned over Southwest R2 ~ 0.5 observed Area burned (105 ha) model Timeseries of area burned model • 3. Benchmark chemistry-climate interactions in the recent + distant past with observations. • Arctic 1980-2010 • Last Glacial Maximum • Equatorial Asia 2000s observed Area burned (105 ha) Area burned in Southwest US may double by 2050. Yue et al., in review

  6. Is the U.S. “warming hole” a signature of cooling due to anthropogenic aerosols? Observed US surface temperature trend 1 No trend between 1930 and 1980. Warming trend after 1980 0 -1 Contiguous US Observed spatial trend in temperatures, 1930-1990 o C GISTEMP 2010 -1 1

  7. 1950 1960 1970 1980 1990 2001 Clearing trend in particles over United States since 1980s suggests possible recent warming. Calculated trend in surface sulfate concentrations Increasing sulfate from 1950-1990s. Decreasing sulfate beginning in 1990s. We applied decadal trends in anthropogenic aerosol to the GISS climate model. Circles show observations. Leibensperger et al., 2012a

  8. Forcing from US anthropogenic aerosols peaks in 1980 -1990s. Direct radiative forcing 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. Indirect radiative forcing Leibensperger et al., 2012a.

  9. Cooling from U.S. anthropogenic aerosols during 1970-1990. Results are from two 5-member ensembles, with and without US anthropogenic aerosols. Cooling is greatest over the Eastern US and North Atlantic. 1 oC cooling at surface over East C Leibensperger et al., 2012b

  10. D Model Temperature 1970-1990 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. C D Cloud Cover D Soil moisture availability % %

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

  12. How have competing trends in BC and SO2 over 20th century affected regional climate across mid-latitudes? Timeseries of US emissions BC U.S. SO2 emissions (Tg S) U.S. BC emissions (Tg C) • Ongoing work. • BC aerosol • warms mid- to upper troposphere • cools surface • stabilizes atmosphere • SO2 cools surface, may augment stabilization. • We will compare model BC with lake core sediments from Adirondacks (Husain et al., 2008) SO2 1850 1950 2000 1900 Deposition in Adirondacks obst observations BC deposition (g m-2 a-1) model 1860 1940 Leibensperger

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