EFFECT OF CLIMATE CHANGE ON U.S. AIR QUALITY Daniel J. Jacob, Harvard University Global change in emissions Change in U.S. air quality Change in climate NO x emissions, 2020

GLOBAL CLIMATE CHANGE SINCE 1850 IPCC [2007]

IPCC PROJECTIONS OF FUTURE WARMING… AND EVALUATION OF PREVIOUS PROJECTIONS IPCC 1995 IPCC 1990 IPCC 2007: IPCC [2007] Mean results from an ensemble of GCMs using the same greenhouse scenarios

PROJECTED WARMING OVER 21 st CENTURY CO 2 trend Global temperature trend CO 2 = 500 ppm

The Eocene climate was warm, even at high latitudes: -palm trees flourished in Wyoming -crocodiles lived in the Arctic -Antarctica was a pine forest -deep ocean temperature was 12°C (today it is ~2°C) -sea level was at least 100 meters higher than today EOCENE (55 to 36 million years ago): The last time in Earth history when atmospheric CO 2 was above 500 ppm. Present models cannot reproduce this warm climate – missing processes? Positive feedbacks could cause abrupt climate change but this is not well understood

OBSERVED DEPENDENCE OF AIR QUALITY ON WEATHER WARNS OF POTENTIALLY LARGE EFFECT OF CLIMATE CHANGE Interannual variability of exceedances of ozone NAAQS # summer days with 8-hour O 3 > 84 ppbv, average for 257 northeast U.S. AIRS sites 1988, hottest on record Ozone is strongly correlated with temperature in observations (R 2 ~ 0.5); reflects (1) chemistry, (2) biogenic VOC emissions, (3) association with stagnation Lin et al. [2001]

USE OZONE-TEMPERATURE CORRELATION TO ESTIMATE EFFECT OF CLIMATE CHANGE ON AIR QUALITY Probability of max 8-h O 3 > 84 ppbv vs. daily max. temperature Projected T change for northeast U.S. in simulated with ensemble of GCMs for different scenarios [IPCC, 2007]  T = 3K Probability Temperature, K Probability of exceedance doubles By 2025,  T = 1-3 K depending on model and scenario; use statistical approach at right to infer increased probability of ozone exceedance for a given region or city assume nothing else changes. Effect is large! Loretta Mickley (Harvard) and Cynthia Lin (UC Davis) Lin et al. [2001] Northeast Los Angeles Southeast

STATISTICAL METHOD TO PROJECT NAAQS EXCEEDANCES FOR A GIVEN LOCATION OR REGION IN A FUTURE CLIMATE Apply ensemble of GCMs to simulate future climate Apply subgrid variability to T from present-day climatology Apply local or regional probability of NAAQS exceedance = f(T) Obtain probability of NAAQS exceedance in future climate assuming constant emissions Obtain daily max T for individual grid squares Obtain daily max T for individual locations

APPLICATION TO PROJECT FUTURE EXCEEDANCES OF OZONE NAAQS IN THE NORTHEAST UNITED STATES Statistical method allows quick local assessment of the effect of climate change, but it has limitations: gives no insight into the coupled effect of changing emissions some fraction of variance unresolved by statistical model no good statistical relationships for PM developed so far Loretta Mickley (Harvard) and Cynthia Lin (UC Davis) Three IPCC(2007) GCMs, downscaled to capture local variability Northeast U.S YEAR Number of exceedance days Average for the 257 AIRS sites of Lin et al. [2001]

EFFECT ON CLIMATE CHANGE ON BOUNDARY LAYER DEPTH Projected A changes in surface T and mixing depth, GISS GCM 3 Change in surface temperature (K) Change in afternoon mixing depth (ratio) Loretta J. Mickley and Shiliang Wu, Harvard Response of boundary layer mixing to climate change is largely driven by local soil moisture; drying of Texas due to NE shift of Bermuda High

EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION Pollution episodes double in duration in 2050 climate due to decreasing frequency of cyclones ventilating the eastern U.S; this decrease is an expected consequence of greenhouse warming. GISS GCM 2’ simulations for 2050 vs. present-day climate using pollution tracers with constant emissions Mickley et al. [2004] summer Mid-latitudes cyclones tracking across southern Canada are the main drivers of northern U.S. ventilation Northeast U.S. CO pollution tracer Clean air sweeps behind cold front Sunday night’s weather map

CLIMATOLOGICAL DATA CONFIRM DECREASE IN FREQUENCY OF MID-LATITUDE CYCLONES OVER PAST 50 YEARS Annual number of surface cyclones and anticylones over North America Cyclone frequency at 30 o -60 o N cyclones anticyclones Agee [1991] McCabe et al. [2001]

COMPREHENSIVE APPROACH FOR INVESTIGATING EFFECT OF CLIMATE CHANGE ON AIR QUALITY Global climate model (GCM) Global chemical transport model (CTM) for ozone-PM Regional climate model (RCM) Regional CTM for ozone-PM boundary conditions input meteorology input meteorology boundary conditions IPCC future emission scenario greenhouse gases ozone-PM precursors Need to run many years to obtain sufficient statistics  expensive! internal EPA project (CIRAQ) and several STAR projects

GLOBAL CHANGE AND AIR POLLUTION (GCAP) GISS GCM GEOS-Chem global CTM MM-5 RCM CMAQ regional CTM boundary conditions input meteorology input meteorology boundary conditions IPCC emission scenario greenhouse gases ozone-PM precursors Applied to global change simulations with IPCC SRES A1 scenario EPA-STAR project : D.J. Jacob and L.J. Mickley (Harvard), J.H. Seinfeld (Caltech), D. Rind (NASA/GISS), D.G. Streets (ANL), J. Fu (U. Tenn.), D. Byun (U. Houston)

EMISSIONS OF OZONE PRECURSORS (A1) GlobalUnited States 2000 emissions % change, emissions% change, NO x, Tg N y -1 Anthropogenic Lightning Soils (natural) % +18% +8% % +21% +11% NMVOCs, Tg C y -1 Anthropogenic Biogenic % +23% % +23% CO, Tg y %87-47% Methane, ppbv (+37%) Shiliang Wu, Harvard Global increase in anthropogenic emissions but 40-50% decreases in U.S.! Climate-driven increases in natural NO x, NMVOC emissions

CHANGES IN SUMMER MEAN 8-h AVG. DAILY MAXMUM OZONE FROM CHANGES IN CLIMATE AND GLOBAL EMISSIONS  2050 emissions & 2000 climate)  2050 emissions & climate) 2000 conditions ( ppb)  2000 emissions & 2050 climate) Shiliang Wu, Harvard

SENSITIVITY OF POLLUTION EPISODES TO GLOBAL CHANGE In northeast and midwest, climate change effect reaches 10 ppbv for high-O 3 events; longer and more frequent stagnation episodes near-zero effect of climate change in southeast Shiliang Wu, Harvard Summer probability distribution of daily 8-h max ozone median 90 th 99 th

CLIMATE CHANGE PENALTY AS ADDED REQUIREMENTS ON EMISSION REDUCTIONS climate change means that we will need to reduce NO x emissions by 50% instead of 40% to achieve the same ozone air quality goals in the northeast Shiliang Wu, Harvard 2000 climate - 40% U.S.NO x emissions 2050 climate -50% NO x emissions 2050 climate -60% NO x emissions

OZONE CLIMATE CHANGE PENALTY WILL BE HIGHER IF WE DON’T REDUCE EMISSIONS Change in mean 8-h daily max ozone (ppb) from climate change with 2000 emissions with 2050 emissions Reducing U.S. anthropogenic emissions significantly mitigates the climate change penalty Shiliang Wu, Harvard

EFFECT OF CLIMATE CHANGE ON POLICY-RELEVANT BACKGROUND (PRB) OZONE 2000 conditions: PRB ozone, ppb   2000 emissions & 2050 climate)  (2050 emissions & 2000 climate)  (2050 emissions & climate) 2050 climate decreases PRB in subsiding regions, increases in upwelling regions 2050 emissions increase PRB due to rising methane, Asian emissions Shiliang Wu, Harvard

EMISSIONS OF PM 2.5 PRECURSORS (A1) GlobalUnited States 2000 emissions % change, emissions% change, SO x, Tg S y -1 Anthropogenic Natural % 0% % NO x, Tg N y -1 Combustion Lightning Soils (natural) % + 18% + 8% % +21% +11% NH 3, Tg N y -1 Anthropogenic Natural % + 0% % + 0% BC, Tg C y % % OC, Tg C y -1 Combustion Biogenic (SOA) % % David Streets, ANL and Shiliang Wu, Harvard

EFFECT OF GLOBAL CHANGE ON ANNUAL MEAN SULFATE CONCENTRATIONS (  g m -3 ) 2000 conditions: sulfate,  g m -3  2000 emissions & 2050 climate)  (2050 emissions & 2000 climate)  2050 emissions & 2050 climate) Shiliang Wu, Harvard Climate change increases sulfate by up to 0.5  g m -3 in midwest (more stagnation), decreases sulfate in southeast (more precipitation)

EFFECT OF GLOBAL CHANGE ON ANNUAL MEAN ORGANIC CARBON (OC) AEROSOL CONCENTRATIONS (  g m -3 ) Shiliang Wu, Harvard Climate change effect is mainly through biogenic SOA and is small because of compensating factors (higher biogenic VOCs, higher volatility) 2000 conditions: OC,  g m -3  2000 emissions & 2050 climate)  (2050 emissions & 2000 climate)  2050 emissions & 2050 climate)

EFFECT OF GLOBAL CHANGE ON ANNUAL MEAN PM 2.5 CONCENTRATIONS (  g m -3 ) Shiliang Wu, Harvard 2000 conditions: PM 2.5,  g m -3  2000 emissions & 2050 climate)  (2050 emissions & 2000 climate)  2050 emissions & 2050 climate) Effect of climate change is small (at most 0.3  g m -3 ) – but this doesn’t account for change in wildfires…

WILDFIRES: A SIGNIFICANT PM 2.5 SOURCE S. California fire plumes, Oct Total carbonaceous (TC) aerosol averaged over all contiguous U.S. IMPROVE sites ~100 IMPROVE sites nationwide Interannual variability in annual mean carbonaceous PM 2.5. is largely determined by wildfires Open fires contribute about 25% of annual mean PM 2.5 in the western U.S., 10% in the east Dominant contributions from western U.S. fires (in the west), Canadian fires (in the northeast), prescribed fires (in the southeast) Park et al. [2007]

INCREASING WILDFIRE FREQUENCY IN PAST DECADES Westerling et al. [2006] Canadian fires [Gillet et al., 2004] Temperature and drought index can explain 50-60% of interannual variability in fires Dominick Spracklen, Harvard

EFFECT OF CLIMATE CHANGE ON WESTERN U.S. WILDFIRES GISS GCM, IPCC A1 scenario, using fire frequency regression on T and drought observed Mean biomass burned per year is projected to increase by 50% in 2050, resulting in 10% increase in annual mean PM 2.5 Dominick Spracklen, Harvard

CONCLUSIONS Climate change over the next decades is likely to have a negative effect on ozone and PM U.S. air quality –effect is most pronounced during pollution episodes –probability of ozone NAAQS exceedances might double in some regions by 2025 if emissions stay constant Climate change for is projected to increase mean summertime ozone by 1-5 ppb (mean 8-h daily max) and up to 10 ppb (pollution episodes) –effect is largest in central and northeast, much weaker in southeast –Model results suggest that this will require an additional 10% decrease in NO x emissions to meet ozone air quality goals in the northeast – the ‘climate change penalty’. Policy-relevant background (PRB) ozone is expected to increase by 1-5 ppb by 2050 (highest in the west) due to rising methane and non-U.S. emissions –climate change partly offsets this effect Effect of climate change on PM 2.5 air quality may be relatively small because of canceling factors –but climate-driven increases in wildfires may be an important issue