INTERACTIONS OF AIR POLLUTION AND CLIMATE CHANGE Daniel J. Jacob How do air pollutants contribute to climate change? How will climate change affect air quality? with funding from NASA, EPA, NSF, EPRI, NOAA

MILLENIAL NORTHERN HEMISPHERE TEMPERATURE TREND [IPCC, 2001; after Mann, 1999] Global mean surface air temperature T o has increased by 0.6 ± 0.2 K over the past century; ocean temperatures, sea level, cloudiness, precipitation also have increased. Gray shading: two standard errors

RADIATIVE FORCING OF CLIMATE CHANGE Incoming solar radiation Reflected solar radiation (surface, air, aerosols, clouds) F out F in IR terrestrial radiation ~ T 4 ; absorbed/reemitted by greenhouse gases, clouds, absorbing aerosols EARTH SURFACE Stable climate is defined by radiative equilibrium: F in = F out Instantaneous perturbation  Radiative forcing  F = F in – F out ; Greenhouse gases   F > 0 (warming) Absorbing aerosols   F > 0 (warming) Scattering aerosols   F < 0 (cooling) General circulation models (GCMs) give  =  T o  F = K m 2 W -1 ;  is relatively insensitive to nature of forcing

GLOBAL RADIATIVE FORCING OF CLIMATE, 1750-present [IPCC, 2001] AIR QUALITY RELATED AQ-related greenhouse forcing: 0.48 (CH 4 ) (O 3 ) (BC) = 1.03 W m -2 …compare to 1.46 W m -2 for radiative forcing by CO 2 Also note –0.50 W m -2 forcing from sulfate and OC aerosols; SO 2 emission reductions result in positive radiative forcing

HANSEN BEST ESTIMATES OF GLOBAL RADIATIVE FORCINGS …including indirect effects [Hansen and Sato, PNAS 2001] AQ-related greenhouse forcing: 0.7 (CH 4 ) (O 3 ) (BC) = 2.0 W m -2 …larger than CO 2 ! Cooling from reflective anthropogenic aerosols: -1.3 (dir.) – 1.0 (indir.) = -2.3 W m -2 …very large!

TROPOSPHERIC OZONE FORCING COULD BE LARGER THAN CURRENT ESTIMATES Standard model: F = 0.44 W m -2 “Adjusted” model (lightning and soil NOx decreased, biogenic hydrocarbons increased): F = 0.80 W m -2 [Mickley et al., JGR 2001] Global simulation of late 19 th century ozone observations in France with the GISS GCM … because of uncertainty on preindustrial ozone (models overestimate 19 th century observations) 3 km altitude

REGIONAL CLIMATE RESPONSE FROM INHOMOGENEOUS RADIATIVE FORCING BY AEROSOLS AND OZONE Assessing the regional climate response to such regional forcings is a very difficult problem; requires observation-based analyses, GCM studies Aerosol radiative forcing over Indian subcontinent during winter monsoon

CLIMATE RESPONSE FROM TROPOSPHERIC OZONE Jun-Aug surface warming (K) in GISS GCM when tropospheric ozone increases from preindustrial to present Difference Tropospheric ozone (0.46 W m -2 )Equivalent CO 2 (0.46 W m -2 ) (white = insignificant or high altitude) Complicated patterns! Largest warmings tend to be downwind of ozone source regions Mickley et al., JGR 2003

DOUBLE DIVIDEND OF METHANE EMISSION CONTROLS FOR AIR QUALITY AND CLIMATE 50% NMVOC 1995 (base ) 50% CH 4 50% NO x 2030 A B1 50% NMVOC 50% CH 4 50% NO x 2030 A B1 IPCC scenario 2030 vs Fossil fuel NO x emissions Global U.S. Methane concentration A1 (pessimistic)+80%-30%+35% B1 (optimistic)+10%-60%+20% # pollution events (O 3 > 80 ppb) Sensitivity simulations with GEOS-CHEM global CTM [Fiore et al., GRL 2002]

EFFECT OF CLIMATE CHANGE ON AIR QUALITY Effect of climate change on air pollution meteorology has so far received no attention in GCMs Well-documented O 3 vs. T relationship warns that effect could be large! Probability of max 8-h O 3 > 84 ppbv vs. daily max. T # summer days with 8-hour O 3 > 84 ppbv, average for northeast U.S. sites Lin et al. [Atm. Env. 2001] analysis of AIRS data 1988, hottest on record!

EFFECT OF FUTURE CLIMATE CHANGE ON U.S. AIR QUALITY: WHAT CAN WE EXPECT? Temperature  Precipitation  Cloudiness  Relative humidity  ? Wind speed  ? Mixing depths?? Frontal passages, circulation?? OzonePM + ++ ? -- likely increaseunclear

EFFECT OF CLIMATE CHANGE ON POLLUTANT VENTILATION GISS GCM simulation of CO and black carbon for transient climate IPCC A1 scenario,  T o = 2 K from 1990 to More frequent pollution episodes in eastern U.S. in 2050 climate; opposite in western U.S. What are the driving meteorological factors? We are investigating. L.J. Mickley, work in progress Summertime frequency distributions of 24-h average CO and BC over northeast U.S.

CLIMATE CHANGE AND INTERCONTINENTAL TRANSPORT OF POLLUTION Surface ozone and sulfate enhancements from present-day Asian anthropogenic emissions GEOS-CHEM simulations for 1997, 2001 What will be the combined effects of rising Asian emissions and climate change?  ozone [Li et al., JGR 2002]  sulfate  Park et al., in prep.]

EPA STAR PROGRAM Assessing the Consequences of Global Change for Air Quality: Sensitivity of U.S. air quality to climate change and future global impacts Six 3-year projects funded in 2003, including GCM studies and model sensitivity analyses GCIAQ project: Harvard (Jacob), Caltech (Seinfeld), NASA/GISS (Rind), DOE/ANL (Streets), U. Tennessee (Fu), EPA/ORD (Gilliland), EPA/OAQPS (Jang) GISS GCM transient climate simulation GEOS-CHEM CTM global O 3 -PM simulation MM5 mesoscale dynamics simulation CMAQ regional O 3 -PM simulation Archive results boundary conditions met. input boundary conditions Compare 2000 and 2050 climates 2050 vs climate

SOME RESEARCH NEEDS FALLING THROUGH THE CRACKS Climate response to regional radiative forcing by aerosols and ozone –Need GCM, observational studies Radiative properties of U.S. aerosols –Need to combine satellite measurements of aerosol optical depth (MODIS, MISR) with in situ observations, models MODIS optical depths (Aug. 2001) Analysis of observed ozone and PM relationships with meteorological variables in present-day climate -- Need to test model simulations of these relationships and develop observation-based diagnostics for predicting effects of climate change Effect of climate change on mercury, POPs -- Need multimedia global models to describe changes in partitioning between reservoirs, atmospheric transport