TROPOSPHERIC OZONE AS A CLIMATE GAS AND AIR POLLUTANT: THE CASE FOR CONTROLLING METHANE Daniel J. Jacob with Loretta J. Mickley, Arlene M. Fiore, Yaping Xiao

MILLENIAL TEMPERATURE TREND [Mann et al., 1999; adopted by IPCC 2001]

RADIATIVE FORCING AS INDEX OF CLIMATE FORCING Climate models (GCMs) indicate  T surface =  F where  (climate sensitivity parameter) ranges from 0.3 to 1.4 K m 2 W -1 depending on the GCM

RADIATIVE FORCING OF CLIMATE, 1750-PRESENT “Kyoto also failed to address two major pollutants that have an impact on warming: black soot and tropospheric ozone. Both are proven health hazards. Reducing both would not only address climate change, but also dramatically improve people's health.” (George W. Bush, June Rose Garden speech) IPCC [2001]

TROPOSPHERIC vs. STRATOSPHERIC OZONE NO x = NO + NO 2 : nitrogen oxide radicals VOC (volatile organic compounds) = light hydrocarbons and substituted organic compounds

TERRESTRIAL RADIATION OBSERVED FROM SPACE Ozone absorption feature at 9.6  m; pressure-broadened in troposphere Scene over Niger Valley, northern Africa Ozone also has “shortwave forcing” by absorption of solar UV radiation

GLOBAL BUDGET OF TROPOSPHERIC OZONE O3O3 O2O2 h O3O3 OHHO 2 h, H 2 O Deposition NO H2O2H2O2 CO, CH 4, VOC NO 2 h STRATOSPHERE TROPOSPHERE 8-18 km Chem prod in troposphere 4900 Chem loss in troposphere 4200 Transport from stratosphere 500 Deposition 1200 Global sources and sinks, Tg O 3 yr -1 (GEOS-CHEM model) Tropospheric ozone is the primary source of OH, the main atmospheric oxidant Pacman of the atmosphere! Main sink for CH 4

NO x EMISSIONS (Tg N yr -1 ) TO THE TROPOSPHERE FOSSIL FUEL 23.1 AIRCRAFT 0.5 BIOFUEL 2.2 BIOMASS BURNING 5.2 SOILS 5.1 LIGHTNING 5.8 STRATOSPHERE 0.2 NO x is the limiting precursor for tropospheric ozone formation

Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS- CHEM model results for 1997 (contours). GEOS-CHEM tropospheric ozone columns for July 1997 GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE Li et al. [2001] Lifetime is < 1 wk in surface air, several wks in free troposphere

CURRENT GENERATION OF OZONE MODELS (IPCC) UNDERESTIMATES OZONE RISE IN 20 th CENTURY Preindustrial ozone models } Observations at mountain sites in Europe [Marenco et al., 1994]

RADIATIVE FORCING BY TROPOSPHERIC OZONE COULD THUS BE MUCH LARGER THAN IPCC VALUE 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., 2001] Global simulation of late 19 th century ozone observations with the GISS GCM

RADIATIVE FORCING FROM TROPOSPHERIC OZONE Mickley et al. [1999]  F = 0.46 W m -2 How good is radiative forcing as an indicator of climate change, when forcing is so heterogeneous? Annual mean values: note heterogeneity

GISS GCM ANALYSIS OF CLIMATIC RESPONSE TO TROPOSPHERIC OZONE CHANGE OVER 20 th CENTURY GCM equilibrium simulation for present-day climate with present vs. preindustrial tropospheric ozone; sea surface temperatures allowed to respond equilibrium climate  T = 0.3 o C  F = 0.46 W m -2 L.J. Mickley, Harvard present-day ozone Preindustrial ozone

INHOMOGENEITY OF CLIMATE RESPONSE TO OZONE CHANGE OVER 20 th CENTURY Greater warming in northern hemisphere (due to more ozone and albedo feedback in Arctic) Strong cooling in stratosphere: Surface Tropospheric ozone 9.6  m Stratospheric ozone L.J. Mickley, Harvard

CLIMATE RESPONSE EXPERIMENTS WITH IDENTICAL GLOBAL RADIATIVE FORCINGS (0.46 W m -2 ) FROM: 1.Tropospheric ozone 2.Uniform tropospheric ozone (18 ppv) 3.Carbon dioxide (25 ppmv) CO 2 is a more effective warming agent at surface In lower stratosphere, CO 2 causes warming while tropospheric ozone causes cooling L.J. Mickley, Harvard

LOWER STRATOSPHERIC COOLING FROM TROPOSPHERIC OZONE IS STRONGEST IN ARCTIC WINTER GCM temperature change in lower stratosphere in DJF ( o C) from increasing tropospheric ozone over 20 th century particularly sensitive region for recovery of ozone layer! L.J. Mickley, Harvard

WHY IS CO 2 MORE EFFECTIVE THAN OZONE FOR SURFACE WARMING AT SAME RADIATIVE FORCING? Correlation of forcing with 500 hPa humidity in tropics (25N-25S) Overlap of CO 2 and H 2 O bands causes CO 2 forcing to shift poleward where ice feedback enhances warming  F CO2 –  F O3 L.J. Mickley, Harvard Ozone CO 2

GCM SURFACE WARMING PATTERNS ( o C) FROM INCREASING TROPOSPHERIC OZONE OVER 20 th CENTURY – JJA SURFACE Difference Tropospheric ozone Equivalent uniform CO 2 (white = insignificant or high altitude) Largest warmings downwind of ozone source regions L.J. Mickley, Harvard

SURFACE OZONE IS THE #1 AIR POLLUTANT IN U.S. EPA/AIRS data [Lin et al., 2001] Mean # summer days ( ) exceeding U.S. ozone air quality standard (84 ppbv, 8-hour average)

ANTHROPOGENIC ENHANCEMENT OF TROPOSPHERIC OZONE BACKGROUND IS A SIZABLE INCREMENT TOWARDS VIOLATION OF U.S. AIR QUALITY STANDARDS (even more so for European standards!) ppbv Europe (seasonal) U.S. (8-h avg.) U.S. (1-h avg.) preindustrial present background Europe (8-h avg.)

SUMMER 1995 MEAN AFTERNOON OZONE IN SURFACE AIR AIRS observations GEOS-CHEM model (r 2 = 0.4, bias=3 ppbv) Fiore et al. [2002] “Background ozone” produced outside the North American boundary layer contributes ppbv to mean surface air concentrations in the model

Combined effects of future anthropogenic emission trends on U.S. ozone air quality and on global 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 Fossil fuel NO x emissions (2020 vs. present) Global U.S. Methane concentration (2020 vs. present) A1+80%-30%+35% B1+10%-60%+20% Fiore et al. [2002] Ozone pollution

HISTORICAL METHANE TRENDS AND IPCC PROJECTIONS Historical methane trend Recent methane trend IPCC projections All IPCC scenarios project increases in CH 4 emissions over next 50 years – but can we try to decrease CH 4 instead?

PRESENT-DAY EMISSIONS OF METHANE: ASIA IS A MAJOR SOURCE REGION Animals Gas venting Gas leakage Landfills Coal mining Termites Soil sink Rice paddies Wetlands Biomass burning Y. Xiao, Harvard

QUANTIFYING ASIAN SOURCES OF METHANE USING AIRCRAFT OBSERVATIONS OF ASIAN OUTFLOW NASA/TRACE-P mission, Feb-Apr 2001

TESTING a priori ASIAN METHANE SOURCE ESTIMATES WITH TRACE-P CORRELATIONS FOR CH 4 -C 2 H 6 -CO GEOS-CHEM vs. observed CH 4 : a priori Asian CH 4 source too high by 25% GEOS-CHEM vs. observed C 2 H 6 /CH 4 : Coal mining CH 4 source likely too high Y. Xiao, Harvard