Interactions Among Air Quality and Climate Policies:Lectures 7 and 8 (abridged versions)

Radiative forcing of climate (1750 to present):Important contributions from air pollutants

IPCC, 2007

Methane: Connecting global climate and ozone pollutionMethane: Connecting global climate and ozone pollution

Arlene M. Fiore (GFDLNOAA)Jason West (University of North Carolina)Larry Horowitz (GFDL/NOAA)Vaishali Naik (GFDL/NOAA)

Year

Variations of CH4 Concentration (ppb) Over the Past 1000 years

[Etheridge et al., 1998]

20001000

800

1200

1600

1400

1000

1500

Historical increase in atmospheric methane

Global Methane Emissions<25% uncertainty in total emissions

ANIMALS90

LANDFILLS +WASTEWATER

50GAS + OIL60

COAL30RICE 40TERMITES

20

WETLANDS180

BIOMASS BURNING + BIOFUEL 30

GLOBAL METHANE SOURCES Natural ~200 (Tg CH4 yr-1 )Anthro ~300 (Tg CH4 yr-1 )

PLANTS?

60-240 Keppler et al., 2006

85 Sanderson et al., 2006

10-60 Kirschbaum et al., 2006

0-46 Ferretti et al., 2006

Clathrates?Melting permafrost?

[EDGAR 3.2 Fast-Track 2000; Olivier et al., Wang et al., 2004]

Modern Methane cycle

• The cycle is relatively simple since the dominent sink is well known (over 90% due to oxidation by OH radicals). The sources are another story.

• The total atmospheric burden is ~5Pg (~1,780ppbv) with an atmospheric lifetime of ~9 years, which is modestly dependent on [CH4] itself.

• Interestingly for a greenhouse gas with over 50% anthropogenic sources, its level in the atmosphere has stopped increasing over the last decade.

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 (ppbv)Can we explain this?Many hypotheses :1. Approach to steady-state2. Source Changes Anthropogenic

Wetlands/plants(Biomass burning)

3. Transport changes4. Sink Changes (CH4+OH) Humidity Temperature OH precursor emissions overhead O3 columns

100 Year IPCC scenarios for methane emissions 100 Year IPCC scenarios for methane emissions

2100 SRES A2 - 2000

Longterm Projections Are Very Uncertain (Tg CH4) to 2100

West et al., 2006

Double dividend of methane controls:Double dividend of methane controls: Improved air quality and reduced greenhouse warmingImproved air quality and reduced greenhouse warming

AIR QUALITY: Change in population-weighted mean 8-hr daily max surface O3 in 3-month “O3 season” (ppbv)

20% anth. NOx

20% anth. CH4

20% anth.

NMVOC

20% anth.CO

CLIMATE: Radiative Forcing (W m-2)

20% anth.

NMVOC

20% anth.CH4

20% anth.NOx

20% anth.CO

Steady-state results from MOZART-2 global chemical transport model

NOx OH

CH4

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

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 can methane 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

0.7

1.4

1.9

10% of anth. emissions

20% of anth. emissions

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

(industrialized nations)

July surface O3 reduction from 30% decrease inanthropogenic CH4 emissions

Globally uniform emission reduction Emission reduction only in Asia

Fiore et al., JGR, 2008

Take Home1. Ozone reduction is independent of location of methane reduction

[pick the cheapest option]2. Ozone reduction is generally largest in polluted regions [high nitrogen oxides] 3. Methane reduction is a win-win for climate and air quality

CONCLUSIONS

• Methane reduction is a win-win for climate and air quality. This is a robust result across global chemical transport models.

• A 10% reduction should pay for itself and another 10% can be paid for with modest carbon credits.

• The maximum impact on air quality is in high NOx regions.

• The location of the methane reduction is not important for either climate or air quality, so pick the least expensive options.

On To Lecture 8

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

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 report draft available at www.htap.org

EUROPE N. AMER. S. ASIA E. ASIA

Will methane emissions increase in the near future?

Anthropogenic CH4 emissions (Tg yr-1)

CurrentLegislation(CLE)Scenario

Dentener et al., ACP, 2005 A2

B2

MFR

Possible Emission Trajectories in the Near Future (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

A

B

C

CLE Baseline

Surface NOx Emissions 2030:2005 ratio

0.3 0.8 1.4 1.9 2.5

A.M. Fiore

Summary: Climate and Air Quality Benefits From CH4 Control

• Significant CH4 reductions can pay for themselves

•Benefits are independent of reduction locationTarget cheapest controls worldwide

• Complementary to NOx, NMVOC controls and maximum benefit in high NOx regions

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

• Decreases hemispheric background O3 Opportunity for joint international air quality-climate management