Connecting Climate and Air Connecting Climate and Air

Quality:Quality:

The Contribution of Methane to The Contribution of Methane to Hemispheric Ozone PollutionHemispheric Ozone Pollution

Center for Atmosphere Ocean Science, New York University March 28, 2007

Arlene M. Fiore(arlene.fiore@noaa.gov)

Acknowledgments: Larry Horowitz, Chip Levy (NOAA/GFDL)

Jason West, Vaishali Naik (Princeton University)Ellen Baum, Joe Chaisson (Clean Air Task Force)

Frank Dentener, Kees Cuvelier (JRC, Italy) The TF HTAP Modeling Team

Funding from Luce Foundation via Clean Air Task Force

U.S. EPA, 2006

Nonattainment Areas (2001-2003 data)

4th highest daily max 8-hr mean O3 > 84 ppbv

The U.S. ozone smog problem is spatially widespread,

affecting >100 million people

Radiative forcing of climate (1750 to present):Important contributions from methane and ozone

IPCC, 2007

NOx

VOC

NOx

VOC

CONTINENT 2 OCEAN

O3

Boundary layer

(0-3 km)

Free Troposphere

CONTINENT 1

OH HO2

VOC, CH4, CO

NONO2

hO3

O3

Hemispheric Pollution

Direct Intercontinental Transport

air pollution (smog)

air pollution (smog)

Stratospheric O3 Stratosphere

~12 km

Air quality-Climate Linkage:CH4, O3 are greenhouse gases

CH4 contributes to background O3 in surface air

A.M. Fiore

Change in 10-model mean surface O3

Attributed mainly to increases in methane and NOx [Prather et al., 2003]

IPCC [2001] scenarios project future growthIPCC [2001] scenarios project future growth

2100 SRES A2 - 2000

Projections of future CH4 emissions (Tg CH4) to 2100

Rising background ORising background O33 has implications has implications for attaining air quality standardsfor attaining air quality standards

20 40 60 80 100

O3 (ppbv)

U.S. 8-hr average

Recent observational analyses suggest that surface O3 background is rising

[e.g. Lin et al., 2000; Jaffe et al., 2003, 2005; Vingarzan, 2004; EMEP/CCC-Report 1/2005 ]

Current background

Pre-industrial background

Europeseasonal

WHO/Europe8-hr average

Future background?

A.M. Fiore

1950s Present1980s

NMVOCs + NOx + CH4??

Ozone abatement strategies evolve as our understanding of the ozone problem

advances

Abatement Strategy:

O3 smog recognizedas an URBAN problem:Los Angeles,Haagen-Smit identifieschemical mechanism

Smog as REGIONAL problem; role of NOx

and biogenic VOCs recognized A GLOBAL perspective:

role of intercontinentaltransport, background

“Methane (and CO) emission control is an effective way of simultaneously meeting air quality standards and abating global warming”

--- EMEP/CCC-Report 1/2005 A.M. Fiore

50% anth. NOx

2030 A1

50% anth. CH4

50% anth.VOC

2030 B1

IPCC scenario

Anthrop. NOx emissions

(2030 vs. present) Global U.S.

Methane emissions(2030 vs. present)

A1 +80% -20% +30%

B1 -5% -50% +12%

1995(base)

50% anth.VOC

50% anth.CH4

50% anth.NOx

2030 A1

2030 B1

Number of U.S. summer grid-square days with O3 > 80 ppbv

Rad

iati

ve F

orc

ing

* (W

m-2)

CH4 links air quality & climate via

background O3

Fiore et al., GRL, 2002

Double dividend of Methane Controls: Decreased greenhouse warming and improved air quality

GEOS-Chem Model (4°x5°)

Impacts of OImpacts of O3 3 precursor reductions on precursor reductions on U.S. summer afternoon surface OU.S. summer afternoon surface O33 frequency frequency

distributionsdistributions

Fiore et al., 2002; West & Fiore, ES&T, 2005

GEOS-Chem Model Simulations (4°x5°)

Results add linearly when both methane and NOx are reduced

CH4 controlsaffect the entireO3 distributionsimilarly(background)

NOx controlsstrongly decreasethe highest O3

(regional pollutionepisodes)

MOZART-2 Global Chemical Transport Model [Horowitz et al., 2003]

Fully represent methane-OH relationship Test directly with observations

3D model structure

NCEP, 1.9°x1.9°, 28 vertical levels

Research Tool:

Methane trends and linkages with chemistry, climate, and ozone pollution

1) Climate and air quality benefits from CH4 controls Characterize the ozone response to CH4 control Incorporate methane controls into a future emission scenario

2) Recent methane trends (1990 to 2004) Are emission inventories consistent with observed CH4 trends? Role of changing sources vs. sinks?

A.M. Fiore

More than half of global methane emissions are influenced by human activities

~300 Tg CH4 yr-1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005]

~200 Tg CH4 yr-1 Biogenic sources [Wang et al., 2004] >25% uncertainty in total emissions

ANIMALS90

LANDFILLS +WASTEWATER

50GAS + OIL60

COAL30RICE 40TERMITES

20

WETLANDS180

BIOMASS BURNING + BIOFUEL 30

GLOBAL METHANESOURCES

(Tg CH4 yr-1)

PLANTS?

60-240 Keppler et al., 2006 85 Sanderson et al., 200610-60 Kirschbaum et al., 2006 0-46 Ferretti et al., 2006

Clathrates?Melting permafrost?

A.M. Fiore

Characterizing the methane-ozone relationship with idealized model simulations

Model approaches a new steady-state after 30 years of simulation

Surface Methane Abundance(ppb)

Tropospheric O3 Burden (Tg)

Is the O3 response sensitive to the location of CH4 emission controls?

Simulation Year

Reduce global anthropogenic CH4 emissions by 30%

A.M. Fiore

Change in July surface O3 from 30% decrease in anthropogenic CH4 emissions

Globally uniform emission reduction Emission reduction in Asia

Target cheapest controls worldwide

Percentage Difference:

Asia – uniformAsia

Enhanced effect in source region

<10% other NH source regions< 5% rest of NH<1% most of SH

A.M. Fiore

Decrease in summertime U.S. surface ozone from 30% reductions in anthrop. CH4 emissions

MAXIMUM DIFFERENCE (Composite max daily afternoon mean ozone JJA)

NO ASIAN ANTH. CH4

Largest decreases in NOx-saturated regions

A.M. Fiore

Tropospheric O3 responds approximately linearly to anthropogenic CH4 emission changes across models

X

MOZART-2 [West et al., PNAS 2006; this work]TM3 [Dentener et al., ACP, 2005]GISS [Shindell et al., GRL, 2005]GEOS-CHEM [Fiore et al., GRL, 2002]IPCC TAR [Prather et al., 2001]

Anthropogenic CH4 contributes ~50 Tg (~15%) to tropospheric O3 burden ~5 ppbv to global surface O3 A.M. Fiore

Multi-model study shows similar surface ozone decreases over NH continents when global

methane is reduced

ANNUAL MEAN OZONE DECREASE FROM 20% DECREASE IN GLOBAL METHANE

0

0.5

1

1.5

2

EU NA SA EA

Full range of 12 individual models

>1 ppbv O3 decrease over all NH receptor regions Consistent with prior studies

ANNUAL MEAN SURFACE OZONE DECREASE DUE TO 20% GLOBAL METHANE REDUCTION

0

0.5

1

1.5

2

EU NA SA EAReceptor region

pp

bv

TF HTAP 2007 Interim report draft available at www.htap.org

EUROPE N. AMER. S. ASIA E. ASIA

A.M. Fiore

0 20 40 60 80 100 120Methane reduction potential (Mton CH4 yr-1)

North AmericaRest of Annex IRest of World

Ozone reduction (ppb)

Cost-saving reductions

<$10 / ton CO2 eq.

All identifiedreductions

How much methane can be reduced?

Comparison: Clean Air Interstate Rule (proposed NOx control) reduces 0.86 ppb over the eastern US, at $0.88 billion yr-1

West & Fiore, ES&T, 2005

IEA [2003] for 5 industrial sectors

0.7

1.4

1.9

10% of anth. emissions

20% of anth. emissions

0 20 40 60 80 100 120 Methane reduction potential (Mton CH4 yr-1)

(industrialized nations)

Will methane emissions increase in the future?

PHOTOCOMP for IPCC AR-4 used CLE, MFR, A2 scenarios for all O3 precursors[Dentener et al., 2006ab; Stevenson et al., 2006; van Noije et al., 2006; Shindell et al., 2006]

Anthropogenic CH4 emissions (Tg yr-1)

CurrentLegislation(CLE)Scenario

Our approach: use CLE as a baseline scenario & apply methane controls

Dentener et al., ACP, 2005 A2

B2

MFR

Emission Trajectories in Future Scenarios (2005 to 2030)

Anthropogenic CH4 Emissions (Tg yr-1)

Control scenarios reduce 2030 CH4 emissions relative to CLE by:

A) -75 Tg (18%) – cost-effective nowB) -125 Tg (29%) – possible with current technologiesC) -180 Tg (42%) – requires new technologies

Additional 2030 simulation where CH4 = 700 ppbv (“zero-out anthrop. CH4”)

A

B

C

CLE Baseline

Surface NOx Emissions 2030:2005 ratio

0.3 0.8 1.4 1.9 2.5

A.M. Fiore

CLE A B C

OZONEMETHANE

+0.16 Net Forcing

+0.080.00 -0.08

Reducing tropospheric ozone via methane controls decreases radiative forcing (2030-2005)

-0.58

CH4=700 ppb

(W m

-2)

Methane Control Scenario

More aggressive CH4 control scenarios offset baseline CLE forcingA.M. Fiore

Future air quality improvements from CH4 emission controls

Percentage of model grid-cell days where surface ozone > 70 ppbv

USA

Europe

2030 European high-O3 events under CLE emissions scenarioshow stronger sensitivity to CH4 than in USA

Cost-effective controls prevent increased occurrence of O3 > 70 ppbv in 2030 relative to 2005

Controls on global CH4 reduce incidence of O3 > 70 ppbv

A.M. Fiore

Summary: Connecting climate and air quality via O3 & CH4

CLIMATE AND AIR QUALITY BENEFITS FROM CH4 CONTROL

• Independent of reduction location (but depends on NOx)Target cheapest controls worldwide

• Robust response over NH continents across models~1 ppbv surface O3 for a 20% decrease in anthrop. CH4

• Complementary to NOx, NMVOC controls

• Decreases hemispheric background O3 Opportunity for international air quality management

A

B

C

CLEAnthrop. CH4 emissions

Tg

yr-1

0 20 40 60 80 100 120Methane reduction potential (Mton CH4 yr-1)

North AmericaRest of Annex IRest of World

Ozone reduction (ppb)

Cost-saving reductions

<$10 / ton CO2 eq.

All identifiedreductions

How well do we understand recent trends in atmospheric methane?

How will future changes in emissions interact with a changing climate?

A.M. Fiore

Observed trend in surface CH4 (ppb) 1990-2004

Data from 42 GMD stations with 8-yr minimum record is area-weighted, after averaging in bands

60-90N, 30-60N, 0-30N, 0-30S, 30-90S

NOAA GMD Network

Global Mean CH4 (ppb)Hypotheses for leveling offdiscussed in the literature:

1. Approach to steady-state 2. Source Changes Anthropogenic

Wetlands/plants(Biomass burning)

3. (Transport)

4. Sink (CH4+OH) Humidity Temperature OH precursor emissions overhead O3 columns

Can the model capture the observed trend (and be used for attribution)?A.M. Fiore

Mea

n B

ias

(pp

b) Overestimates

interhemispheric gradient

Bias and correlation vs. observed surface CH4: 1990-2004

r2

Correlates poorly at high N latitudes

S Latitude N

1710

1720

1730

1740

1750

1760

1770

1780

1790

1990 1992 1994 1996 1998 2000 2002 2004

Global Mean Surface Methane (ppb)OBSERVEDMOZART-2

Captures flattening post-1998 but underestimates abundance

Overestimates 1990-1997 but matches trend

BASE simulation EDGAR 2.0 emissions held constant

Estimates for changing methane sources in the 1990s

547

Tg

CH

4 yr

-1

EDGAR anthropogenic inventory

Biogenic adjusted to maintainconstant total source

BASE ANTH

200

210

220

230

240

250

260

270

1990 1995 2000 2005

Inter-annually varying wetland emissions1990-1998 from Wang et al. [2004](Tg CH4 yr-1); different distribution

Apply climatological mean (224 Tg yr-1) post-1998

ANTH + BIOA.M. Fiore

Mea

n B

ias

(pp

b)

ANTH+BIO simulation with time-varying EDGAR 3.2 + wetland emissions improves: Global mean surface conc. Interhemispheric gradient Correlation at high N latitudes

1710

1720

1730

1740

1750

1760

1770

1780

1790

1990 1995 2000 2005

OBSBASEANTHANTH+BIO

r2

Fiore et al., GRL, 2006 S Latitude N

Bias & Correlation vs. GMD CH4 observations: 1990-2004

Global Mean Surface Methane (ppb)

How does meteorology influence methane abundances?

]CH][OH[

]CH[

4

4

k=

Temperature(88% of CH4 loss is below 500 hPa )

HumidityPhotolysisLightning NOx

Why does BASE run with constant emissions level off post-1998?

Examine sink

What drives the change in methane lifetime in the model?

CH4 Lifetime ( against Tropospheric OH

= 0.17 yr = 1.6%)

A.M. Fiore

Small increases in temperature and OH shorten the methane lifetime against tropospheric

OH

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

climT climOH BASE

T(+0.3K)

+ =

OH(+1.2%) BASE

Deconstruct (-0.17 years) from 1991-1995 to 2000-2004 into individual contributions by varying OH and temperature separately

OH

Global Lightning NOx (TgN yr-1)

An increase in lightning NOx drives the OH increase in the model

But lightning NOx is highly parameterized …how robust is this result?

A.M. Fiore

Additional evidence for a global lightning NOx increase?

NCEP(nudged)

Lightning NOx % change (91-95 to 00-04)

Estimate lightning NOx changes using options available in the GFDL Atmospheric General Circulation Model:• Convection schemes (RAS vs. Donner-deep) • Meteorology (free-running vs. nudged to NCEP reanalysis)

c/o L.W. Horowitz

More physically-based lightning NOx scheme [Petersen et al., 2005]

Evidence from observations?

LIS/OTDFlash counts

Magnetic field variations in the lower ELF range[e.g. Williams, 1992;Füllekrug and Fraser-Smith, 1997; Price, 2000]Negev Desert

Station, Israel

Lightning NOx increase robust; magnitude depends on meteorology

free-running GCM

DonnerMOZART RAS

A.M. Fiore

Summary: Connecting climate and air quality via O3 & CH4

CLIMATE AND AIR QUALITY BENEFITS FROM CH4 CONTROL

• Independent of reduction location (but depends on NOx)Target cheapest controls worldwide

• Robust response over NH continents across models~1 ppbv surface O3 for a 20% decrease in anthrop. CH4

• Complementary to NOx, NMVOC controls

• Decreases hemispheric background O3 Opportunity for international air quality management

METHANE TRENDS FROM 1990 TO 2004

• Simulation with time-varying emissions and meteorology best captures observed CH4 distribution

• Model trend driven by increasing T, OH

• Trends in global lightning activity?

Potential for climate feedbacks (on sources and sinks)0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

climT climOH BASE

+ =T OH BASE

OH 91-95 to 01-04

1710

1720

1730

1740

1750

1760

1770

1780

1790

1990 1995 2000 2005

OBSBASEANTHANTH+BIO

Methane (ppb)

A

B

C

CLEAnthrop. CH4 emissions

Tg

yr-1

0 20 40 60 80 100 120Methane reduction potential (Mton CH4 yr-1)

North AmericaRest of Annex IRest of World

Ozone reduction (ppb)

Cost-saving reductions

<$10 / ton CO2 eq.

All identifiedreductions

A.M. Fiore