1. The Double Dividend of Methane Control
(Fiore et al., GRL, October 2002)
Arlene Fiore
GWXIV
Cambridge, MA
May 28, 2003
BIOMASS
BURNING 20
ANIMALS 90
WETLANDS
180
LANDFILLS 50
GLOBAL METHANE
SOURCES (Tg CH4 yr-1)
GAS 60
TERMITES 25
COAL 40
RICE 85

2. IPCC [2001] Projections of Future CH4 Emissions (Tg CH4) to 2050
Atmospheric CH4: Past Trends, Future Predictions
IPCC [2001] Projections of Future CH4 Emissions (Tg CH4) to 2050
Variations of CH4 Concentration (ppbv)
Over the Past 1000 years
[Etheridge et al., 1998]
Scenarios
1600
900
A1B
A1T
A1F1 A2 B1 B2
IS92a
1400
800
1200
700
1000
800
600
1000
1500
2000
2000
2020
2040
Year
Year

3. Radiative Forcing of Climate, 1750-Present: Important Contributions from Methane and Ozone
IPCC [2001]
Level of scientific understanding

4. CH4 itself is an important greenhouse gas, and links climate with air pollution via its influence on tropospheric ozone O3
greenhouse gas
Free Troposphere hn
NO2 NO
Hemispheric Pollution OH
HO2
Direct Intercontinental Transport
Boundary layer
(0-2.5 km)
VOC, CH4, CO
air pollution (smog)
NOx
NMVOCs O3
NOx
NMVOCs O3
air pollution (smog)
CONTINENT 1
CONTINENT 2
OCEAN

5. Ozone abatement strategies evolve as our understanding of the O3 problem improves
O3 smog recognized
as an URBAN problem: Los Angeles,
Haagen-Smit identifies
chemical mechanism
Smog considered
REGIONAL problem;
role of biogenic
VOCs discovered
A GLOBAL perspective:
role of intercontinental
transport, background
1980s
Present
1950s
Abatement Strategy:
NMVOCs
+ NOx
+ CH4??

6. Background (ppbv) in GEOS-CHEM Model,
What is background O3 over the United States?
Summer p.m. Observations at Harvard Forest, Massachusetts Data from Munger et al., [1996, 1998]
Mean Afternoon O3
Background (ppbv) in GEOS-CHEM Model,
Summer 1995
r2 = 0.74
U.S. Ozone
Standard
Intercept
30 ppb
background
(clean air)
Ozone (ppbv)
Range of background
Estimated from observations
Background is tagged as
ozone produced outside
the N. American boundary
layer (surface-700 hPa)
NOy-NOx (ppbv)
(Index of Aged Pollution)
Fiore et al., JGR, August, 2002.

7. TOOL: GEOS-CHEM 3D Tropospheric Chemistry Model [Bey et al., 2001]
QUESTION: Can we simultaneously mitigate air pollution and greenhouse warming?
TOOL: GEOS-CHEM 3D Tropospheric Chemistry Model [Bey et al., 2001]
(uses assimilated meteorology; 20 s; 4ºx5º or 2ºx2.5º horiz. resn.)
MODEL EVALUATION:
Mean July p.m. O3 (ppbv) in U.S. surface air
Model Bias: 2 ppbv, r2 = 0.7
GEOS-CHEM captures: regional high-O3 episodes, observed O3 vs. (NOy-NOx),
observed tightening of O3 distribution from 1980 to 1995
[Fiore et al., JGR, August, 2002]

8. Impacts of future changes in global anthropogenic emissions on climate: Change in radiative forcing (W m-2) relative to 1995 base case
NOx  OH 
CH4
50%
anthr.
NMVOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1
IPCC scenario
Anthrop. NOx emissions
(2030 vs. present)
Global U.S.
Methane emissions A1
+80%
-20%
+30% B1
-5%
-50%
+12%

9. Change in summer afternoon O3 in surface air over the U.S.
Relative to 1995 base year (mean 51 ppbv, background 23 ppbv)
Mean O3
Background O3*
Degradation of U.S.
air quality from rise
in global emissions
despite domestic
reductions
Change in O3 (ppbv)
50%
anthr.
NMVOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1
*produced outside the North American boundary layer (surface-700 hPa)

10. Number of summer grid-square days with O3 > 80 ppbv
Impacts of future changes in global anthrop. emis. on U.S. air quality:
Number of summer grid-square days with O3 > 80 ppbv
Increase in U.S.
pollution events
despite domestic
decline in anthrop.
emissions
1995
(base)
50%
anthr.
VOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1
IPCC 2030
scenario
Anthrop. NOx emissions
Global U.S.
Methane emissions A1
+80%
-20%
+30% B1
-5%
-50%
+12%

11. Rising emissions from developing countries lengthen the O3 pollution season in the United States
Degradation of U.S.
air quality from rise
in global emissions
despite domestic
reductions
1995 Base Case
2030 A1

12. Double dividend of methane emissions reductions: (1) improve air quality everywhere (2) reduce greenhouse warming
Free Troposphere
CH4 emissions
global impact:
Lower background O3
Negative radiative forcing
CH4
Intercontinental transport,
global O3 background
increases in
2030 A1 simulation O3
Boundary layer
(0-2.5 km)
NOx emissions local impact;
little effect on climate
Chemical loss
Deposition
NOx
NMVOCs
NOx
NMVOCs O3 O3
CONTINENT 1
CONTINENT 2
OCEAN