1. Investigation of chemistry-climate interactions, with a closer look at the U.S. warming hole Loretta J. Mickley Eric Leibensperger, Xu Yue, Daniel Jacob, Jennifer Logan David Rind, GISS Jed Kaplan, U Geneva 2009 wildfire in Southern California

2. Millions of people in US live in areas with unhealthy levels of ozone or particulate matter (PM 2.5 ). Number of people living in areas that exceed the national ambient air quality standards (NAAQS) in 2010. Bars on barplot will change with changing emissions. Climate change could also change the size of these bars, by changing the day- to-day weather. Ozone daily maximum 8-hour average PM 2.5 24-hour average or annual average

3. Particles affect solar radiation directly … and also indirectly by modifying cloud properties. Pollution off U.S. east coast Black carbon California fire plumes Aircraft contrails and cirrus over Europe Light-colored particles reflect sunlight and cool the earth’s surface. cooler 3

4. 4 Life cycle of particulate matter (PM, aerosols) nucleation coagulation condensation wildfires combustion sea salt...... cycling ultra-fine (<0.01  m) fine (0.01-1  m) cloud (1-100  m) combustion volcanoes agriculture biosphere coarse (1-10  m) scavenging precursor gases SO 2 -- sulfur dioxide NOx -- nitrogen oxides Soup of chemical reactions NOx VOCs Organic carbon SO 2 NH 3 SO 2 VOCs -- volatile organic compounds NH 3 -- ammonia Black carbon dust

5. 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

6. Wildfire in the western United States in the mid-21st century Consequences for air quality. Rim fire, Yosemite Natl Park, 2013 Climate changeAir Quality

7.  Hayman fire, June 8-22, 2002  56,000 ha burned  30 miles from Denver and Colorado Springs Colorado Dept. of Public Health and Environment Vedal et al., 2006 June 8, 2002 June 9, 2002 PM 10 = 372 μg/m 3 PM 2.5 = 200 μg/m 3 Standard = 35 µg/m 3 PM 10 = 40 μg/m 3 PM 2.5 = 10 μg/m 3 Unhealthy air quality in Denver Effects of wildfires on air quality in cities in Western US can be very dramatic.

8. Fire activity had a big impact on California air quality in 2013. Unhealthy air Very unhealthy air Rim Fire Aug 28 Aug 30 Timeseries of 3-hour average PM 2.5 concentrations in Foothills Area August 20 August 31 PM2.5 (  g m -3 ) Hazardous levels > 250  g m -3 Will fire change in the future climate? Very unhealthy

9. Gillett et al., 2004 Area burned in Canada has increased since the 1960s, correlated with temperature increase. Westerling et al., 2007 Increased fire frequency over the western U.S. since 1970, related to warmer temperatures and earlier snow melt. Observations suggest that fires are increasing in North America. 1970 2000 5 yr means area burned obs temperature 19602000

10. IPCC AR4 models show increasing temperatures across North America by 2100 in A1B scenario. Models show increases of JJA temperatures of ~ 3K in Western US. Results for precipitation changes are not so clear.  Temperature JJA, o C  Precipitation JJA, % IPCC, 2007 most models few models Number of models showing increased precipitation.

11. How do we predict fires in a future climate? We don’t have a good mechanistic approach for modeling wildfires. JJA Temperature increase by 2100 Use ensemble of climate models to gain confidence in prediction. Relationship between observed meteorology + area burned + Future meteorology Future area burned Start with the past. 2 approaches

12. Regression approach. Regress meteorological variables and fire indexes onto annual mean area burned in each of six ecoregions with a stepwise approach. PNW ERM NMS RMF DSW CCS Ecoregions are aggregates of those in Bailey et al. (1994) Identify the meteorological variables and fire indexes that best predict area burned. Include lagged met variables. For example, Area burned in Nevada/ semi-desert = f ( + T summer max that year + RH and rainfall previous years) Best predictors: Temp, RH, precip, Build-up Index, Drought code, Duff moisture code.

13. Predicted fires match observed area burned reasonably well. Least best fit is in Southern California. ObsFit Area burned in many ecoregions depends on previous year’s relative humidity, rainfall, or temp. Yue et al., 2013 CCS PNW NMS DSW RMF ERM

14. Relationship between observed meteorology + area burned + Future meteorology Future area burned Start with the past.

15. Use of an ensemble of 15 climate models improves confidence in the results. Changes in 2050s climate in the West. Temperature increases 2-2.5 K. Changes in precip and relative humidity are small and not always robust. Next step: apply meteorology from climate models to the two fire prediction schemes. Yue et al., 2013

16. Wildfire area burned increases across the western United States by the 2050s timeframe. Relationship between observed meteorology + area burned + Future meteorology Future area burned Results from regressions approach. Shown are median results. Yue et al., 2013

17. Predicted area burned shows large increases in 2050s during peak months. future present-day X4 increase X2 increase Yue et al., 2013 Units = 10 4 hectares

18. GEOS-CHEM Global chemistry model Ensemble of climate models Median area burned Emissions = area burned x fuel consumption x emission factors How will changing area burned affect air quality? Future air quality Future meteorology

19. Yue et al., 2013 Organic particles increase in future atmosphere over the western U.S. in summer, especially during extreme events. Change in summertime mean organic PM 2.5 in ~2050s, relative to present-day. Wildfires may swamp efforts to regulate air quality in future.  Organic Carbon, OC Ma 2050s Present- day doubling May-Oct JJA Cumulative probability of daily mean concentrations of OC, Rocky Mountains

20. What do these increases in wildfire aerosol mean for human health? Ongoing project with Yale will look at health impacts of these increases. Yue et al., 2013 % area burned % OC particles

21. Ratio of 2050s area burned to present-day Ecoregions West to East Alaska Boreal Cordillera How will wildfire change in a changing climate in Canada? Ratio of 2050s area burned to present-day Area burned increases in the West due to: Higher temperatures More frequent blocking high pressure systems. Increased rainfall in Central and eastern Canada blunt these effects. Yue, in progress

22. Pittsburgh, 1973 Regional climate effects of 1950-2050 trends in US anthropogenic aerosols. AerosolsClimate change

23. Observed US surface temperature trend GISTEMP 2010 What caused the U.S. warming hole of the 20th century? Observed spatial trend in temperatures, 1930-1990 No trend between 1930 and 1980. Warming trend after 1980 Contiguous US 1 0 o C 1

24. Increasing sulfate from 1950-1990s. 19501960 19701980 19902001 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. Decreasing sulfate by 2001.

25. Spin-up Constant aerosols everywhere Zeroed US aerosols, constant elsewhere 20102050 We first perform a pilot study: Constant aerosols vs. zeroed US aerosols A1B scenario of greenhouse gases Forcing due to aerosol removal over US Model setup causes large warming over East. By comparison, global  F from CO 2 is +1.8 Wm -2. GISS climate model

26. Results from pilot study: Removal of aerosol sources over US increases annual mean surface temperatures by 0.5 o C. Warming due to 2010-2050 trend in greenhouse gases. Additional warming due to zeroing of US aerosols Mickley et al., 2012 white areas = insignificant differences Summertime temperatures increase as much as 1.5 o C. Only direct aerosol effect included.

27. Warming begins immediately and persists through the decades. Mickley et al., 2012 Warming due to aerosol removal is strongest in late summer / early fall Heatwaves show 1-2 K increase.  Temperature, 2050s Daily max T Daily mean T A1B Change in surface temperatures due to aerosol removal, Northeast US

28. Climate response of Northeast to aerosol removal 28 Shift from increased latent flux to increased sensible and LW flux in late summer. Increased diurnal temperature range, higher Tmax Increased solar flux in July-October Warming, especially in late summer, early fall. Increased sunlight depletes soil moisture by late summer. Reduced cloud cover and relative humidity Daily max T Daily mean T LW Latent heat Sensible heat Low cloud cover Rel humidity    

29. LW Latent heat Sensible heat  Soil moisture depletes through summer. Cloud cover diminishes in response. Shift from increased latent flux to increased sensible and LW flux in late summer. Feedbacks involving soil moisture and low cloud cover amplify local temperature response in Aug-Oct period. Diffuse warming Local warming

30. We applied decadal trends in anthropogenic aerosol to the GISS climate model. Increasing sulfate from 1950-1990s. Decreasing sulfate beginning in 1990s. 19501960 19701980 19902001 Leibensperger et al., 2012a Calculated trend in surface sulfate concentrations Next, we perform a more realistic set of simulations, with changing emissions, 1950-2050. Circles show observations.

31. Leibensperger et al., 2012a. Direct radiative forcing Indirect radiative forcing Forcing from US anthropogenic aerosols peaks in 1980 -1990s. 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 from clouds is about the same magnitude as direct effect. Net  F

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

33.  Model Temperature 1970-1990 C  Soil moisture availability  Cloud Cover % Cooling over U.S. is not co-located with aerosol burden. Local changes in cloud cover and soil moisture amplify the cooling effect. Cooling over North Atlantic strengthens Bermuda High, increasing onshore flow of moisture from Gulf of Mexico. Results are controversial.

34. Westward extent of Bermuda High 2000 1980 1950 NCEP ERA Reference longitude East West Li et al., 2011 Observations show intensification of the Bermuda High during the 1980s and early 1990s, apparently consistent with aerosol loading. Variation of western edge of Bermuda High during JJA, 1948-2007. Edge = 1560-gpm contour line at 850 hPa. Period of greatest aerosol loading 1948-19771978-2007 Shift westward What about effect of Pacific Decadal Oscillation?

35. 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

36. U.S. BC emissions (Tg C) 1850 U.S. SO 2 emissions (Tg S) 1900 1950 2000 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 Sulfate cools surface, may augment stabilization. We will compare model BC with lake core sediments from Adirondacks (Husain et al., 2008) and with ice cores from J. McConnell. BC deposition (g m-2 a-1) 1860 1940 obst observations model Deposition in Adirondacks Leibensperger, Cusworth, and Mickley

37. Take home messages. Area burned by wildfires may increase significantly across western North America by 2050s, depending on the ecosystem. Increased smoke from wildfires may thwart efforts to regulate air quality in coming decades. This is a climate penalty. Decreases in aerosol loading may have unintended consequences for regional climate, leading to warming. Wildfires in Quebec the same day. Haze over Boston on May 31, 2010