Atmospheric Methane Distribution, Trend, and Linkage with Surface OzoneArlene M. Fiore1 (arlene.fiore@noaa.gov), Larry W. Horowitz1, Ed Dlugokencky2, J. Jason West3

1NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ 2NOAA Global Monitoring Division, Earth System Research Laboratory, Boulder, CO 3Atmospheric and Oceanic Sciences Program and Woodrow Wilson School, Princeton University, Princeton, NJ

1. Introduction

REFERENCESDentener, F., et al. (2003), J. Geophys. Res., 108, 4442, doi:10.1029/2002JD002916. Dlugokencky, E.J., et al. (2003), Geophys. Res. Lett., 30, 1992, doi:10.1029/2003GL018126. Dlugokencky, E.J., et al. (2005), J. Geophys. Res., 110, D18306, doi:10.1029/2005JD006035. Horowitz, L.W., et al. (2003), J. Geophys. Res., 108, 4784, doi:10.1029/2002JD002853.

What is driving observed CH4 trends? Does CH4 source location influence the O3 response?

• Methane (CH4) emission controls can be a cost-effective strategy for abating both global surface ozone (O3) and greenhouse warming [West and Fiore, 2005; see also poster by West et al.]

previous modeling studies used fixed CH4 concentrations and globally uniform changes, but CH4 is observed to vary spatially and temporally

• The major sink of CH4 is reaction with tropospheric OH; emissions of CH4 are shown in Section 2

• Surface CH4 rose by ~5-6 ppb yr-1 from 1990-1999, then leveled off (Section 3), possibly reflecting: (1) source changes of CH4 [e.g. Langenfelds et al., 2002; Wang et al., 2004] or other species that influence OH [e.g. Karlsdóttir and Isaksen, 2000] (2) meteorologically-driven changes in the CH4 sink [e.g. Warwick et al., 2002; Dentener et al., 2003; Wang et al., 2004] (3) an approach to steady-state with constant lifetime [Dlugokencky et al., 2003]

• Ozone response is largely independent of CH4 source location

• 30% decrease in global anthropogenic CH4 emissions reduces JJA

U.S. surface afternoon O3 by 1-4 ppbv

• BASE simulation (constant emissions) captures observed rate of

CH4 increase from 1990-1997, and leveling off post-1998

• ANTH emissions improve modeled CH4 post-1998

• Wetland emissions in ANTH+BIO best match the observed CH4

seasonality, interhemispheric gradient, and global mean trend

• CH4 decreases by ~2% from 91-95 to 00-04 due to warmer

temperatures (35%) and higher OH (65%, resulting from a ~10% increase in lightning NOx emissions)

Future research should:• consider climate-driven feedbacks from fire and biogenic emissions on

CH4

• develop more physically-based parameterizations of lightning NOx emissions to

determine whether higher emissions are a robust feature of a warmer climate

Van Aardenne, J.A., F. Dentener, J.G.J. Olivier and J.A.H.W. Peters (2005), The EDGAR 3.2 Fast Track 2000 dataset (32FT2000).Wang , J.S., et al. (2004), Global Biogeochem. Cycles, 18, GB3011, doi:10.1029/2003GB002180. Warwick, N.J., et al. (2002), Geophys. Res. Lett., 29 (20), 1947, doi:10.1029/2002GL015282 West, J.J. and A.M. Fiore (2005), Environ. Sci. & Technol., 39, 4685-4691.

Karlsdóttir, S., and I.S.A. Isaksen (2000), Geophys. Res. Lett., 27 (1), 93-96. Langenfelds, R.L., et al. (2002), Global Biogeochem. Cycles, 16, 1048, doi:10.1029/2001GB001466.Olivier, J.G.J., et al. (1999), Environmental Science & Policy, 2, 241-264.Olivier, J.G.J. (2002) In: "CO2 emissions from fuel combustion 1971-2000", 2002 Edition, pp. III.1-III.31. International Energy Agency (IEA), Paris. ISBN 92-64-09794-5.

3. Influence of Sources on Surface CH4 Distribution and Trend

1710

1720

1730

1740

1750

1760

1770

1780

1790

1990 1995 2000 2005

OBSERVED

BASE too low post-1998

ANTH improves CH4 vs. OBS post-1998

ANTH+BIO best captures measured abundances

Global mean surface CH4 concentrations as measured (or sampled in the model) at 42 Global Monitoring Division (GMD) stations [e.g. Dlugokencky et al., 2005] with an 8-year minimum record. Values are area-weighted after averaging in latitudinal bands (60-90N, 30-60N, 0-30N, 0-30S, 30-90S).

Mean model bias and correlation with 1990-2004 monthly mean surface GMD observations

BASEANTHANTH+BIO

-90 -50 0 50 90Latitude

100

50

0

-50

-100

Bia

s (p

pb

)r2

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

BASE wetlandemissions yield a closer match with observedCH4 in tropics

nm

ol/

mo

l =

pp

b i

n d

ry a

ir

2. Methane in the MOZART-2 CTM

BASEConstant emissions (1990)

Sensitivity simulations applying different CH4 emission inventories:

ANTH Time-varying anthropogenic emissions

ANTH + BIO Time-varying anthropogenic and wetland emissions

EDGAR v3.2 1990,1995 and “FAST-TRACK” 2000 anthrop. emissions [Olivier, 2002; van Aardenne et al., 2005]

Biogenic source adjusted to match BASE 1990 total

200

210

220

230

240

250

260

270

1990 1995 2000 2005

Tg

CH

4 yr

-1

Apply climatological mean post-1998, scaled to equal biogenic total in ANTH (224 Tg yr-1)

From Wang et al. [2004]

6. Conclusions

OBS (GMD) BASE ANTH ANTH+BIO

ANTH+BIO improves:(1) High N latitude seasonal cycle, (2) Trend, (3) Low bias at S Pole, especially post-1998

1900

1850

1800

184018201800178017601740

1800

1750

1700

1740

1720

1700

1680

1660

1640

1990 1995 2000 2005

Alert (82.4N,62.5W)

South Pole (89.9S,24.8W)

Mahe Island (4.7S,55.2E)

Midway (28.2N,177.4W)

Surface CH4 concentrations at selected GMD stationsn

mo

l/m

ol

= p

pb

in

dry

air

Tropospheric O3 response toanthropogenic CH4 emission

changes is approximately linear

5. Ozone Response to CH4 Emission Controls

Stronger sensitivity in NOx-saturated regions (Los Angeles), partially due to local O3 production from CH4

O3 change independent of CH4 source location except for <10% effects in the Asian source region

Latitudinal distribution of 1990 CH4 emissions for cases shown below

BASEANTHANTH+BIO

-90 -50 0 50 90

Latitude

80

60

40

20

0

Tg

CH

4 yr

-1

4. Meteorologically-driven Changes in the CH4 Lifetime

Meteorological drivers for trend Not just an approach to steady-state

Global mean surface CH4 in BASE simulation (constant emissions)

1740

1750

1760

1770

1780

1790

1800

1810

1990 1995 2000 2005 2010 2015 2020

Recycled NCEP 1990-2004

CH4 Lifetime Against Tropospheric OH

Mean annual CH4 lifetime shortens

9.9

10

10.1

10.2

10.3

10.4

10.5

1990 1995 2000 2005

10.4010.23

Deconstruct from 91-95 to 00-04 into individual contributions by varying T and OH

separately

OH increases in the model by +1.4% due to a 0.3 Tg N yr-1 increase in lightning NOx

ANTH+BIO bestcaptures the CH4

interhemisphericgradient

ANTH+BIO improves the correlation withwith observationsat high northernlatitudes

547

Tg

CH

4 yr

-1

Biogenic andbiomass burning fromHorowitz et al. [2003]

Anthropogenic(energy, rice, ruminants)from EDGAR 2.0[Olivier et al., 1999]

Ch

an

ge in

mean

()

fro

m90-9

5 t

o 0

0-0

4 (

years

)

+ =

BASET(+0.3K) OH(+1.4%)

• ~100 gas and aerosol species, ~200 reactions• NCEP meteorology 1990-2004• 1.9o latitude x 1.9o longitude x 64 vertical levels• detailed description in Horowitz et al. [2003]

Change in summertime U.S. afternoon surface O3

MEAN DIFFERENCE MAX DAILY DIFFERENCE

ZERO ASIAN ANTHROP. CH4

GLOBAL 30% DECREASE IN ANTHROP. CH4

ppbv

Simulations of anthropogenic CH4 emission reductions (relative to BASE)

trop

osp

heric O

3 (Tg

)

Year

su

rfac

e C

H4

(pp

b)

Change in CH4 and O3 approaching

steady-state after 30 years

BASE captures observed rate of increase 1990-97and leveling off after 1998

547 548 557

Tg

CH

4 yr

-1

1990 1995 2000

MOZART-2 (this work)TM3 [Dentener et al., ACPD, 2005]GISS [Shindell et al., GRL, 2005GEOS-CHEM [Fiore et al., GRL, 2002]IPCC TAR [Prather et al., 2001]

X

-400

-350

-300

-250

-200

-150

-100

-50

0

1 6 11 16 21 26 31

-12

-10

-8

-6

-4

-2

0

0 4 9 13 17 21 29