Transcript Atmospheric Methane Distribution and Trends: Impacts on Climate and Ozone Air Quality Arlene M.

Atmospheric Methane
Distribution and Trends:
Impacts on Climate and
Ozone Air Quality
Arlene M. Fiore
Larry Horowitz (NOAA/GFDL)
Jason West (Princeton)
Ed Dlugokencky (NOAA/GMD)
Earth, Atmospheric, and Planetary Sciences
Department Seminar
Massachusetts Institute of Technology
December 16, 2005
Atmospheric CH4: Past Trends, Future Predictions
Variations of CH4 Concentration (ppb)
Over the Past 1000 years
[Etheridge et al., 1998]
IPCC [2001] Projections of Future
CH4 Emissions (Tg CH4) to 2050
Scenarios
1600
900
1400
800
1200
700
1000
800
1000
A1B
A1T
A1F1
A2
B1
B2
IS92a
600
1500
Year
2000
2000
2020
Year
2040
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]
BIOMASS BURNING
+ BIOFUEL
ANIMALS
30
WETLANDS
90
180
GLOBAL METHANE
SOURCES
(Tg CH4 yr-1)
TERMITES RICE 40
20
COAL
30
LANDFILLS +
WASTEWATER
50
GAS + OIL
60
Air quality-Climate Linkage:
CH4, O3 are important greenhouse gases
CH4 contributes to background O3 in surface air
Free Troposphere
hn
O3
NO2
NO
OH
HO2
Global Background O3
Direct Intercontinental Transport
Boundary layer
(0-3 km)
VOC, CH4, CO
NOx
NMVOCs
CONTINENT 1
air pollution (smog)
O3
air pollution (smog)
OCEAN
NOx
NMVOCs
CONTINENT 2
O3
Observations indicate historical increase in background
ozone; IPCC scenarios project future growth
Ozone at European mountain sites
1870-1990 [Marenco et al., 1994].
Change in 10-model mean July
surface O3 [Prather et al., 2003]
2100 SRES A2 - 2000
Attributed mainly to increases in methane and NOx
[Wang et al., 1998; Prather et al., 2003]
Adapted from J. West
Rising background O3 at northern mid-latitudes has
implications for attaining air quality standards
Pre-industrial
background
20
new CA
standard
8-hr avg
Europe
seasonal
40
Current background
60
WHO/Europe
8-hr average
80
U.S. 8-hr
average
100
O3 (ppbv)
Analyses of surface O3 from North American and European
monitoring sites indicate increasing background
[Lin et al., 2000; Jaffe et al., 2003,2005; Vingarzen et al., 2004;
EMEP/CCC-Report 1/2005 ]
Radiative Forcing of Climate from Preindustrial to Present:
Important Contributions from Methane and Ozone
Hansen, Scientific American, 2004
Approach: Use 3-D Models of Atmospheric Chemistry to examine
climate and air quality response to emission changes
GEOS-CHEM
[Bey et al., 2001]
•
•
•
•
GEOS GMAO meteorology
4°x5°; 20 s-levels
GEIA/Harvard emissions
Uniform, fixed CH4
MOZART-2
[Horowitz et al., 2003]
•
•
•
•
3-D model structure
NCEP meteorology
1.9°x1.9°; 28 s-levels
EDGAR v. 2.0 emissions
CH4 EDGAR emissions for
1990s
Radiative Forcing (W m-2)
Double dividend of Methane Controls:
Decreased greenhouse warming and improved air quality
Number of U.S. summer gridsquare days with O3 > 80 ppbv
50% 50% 50% 2030 2030
1995 50% 50% 50% 2030 2030
anth. anth. anth. A1 B1
(base) anth. anth.anth. A1 B1
VOC CH4 NOx
VOC CH4 NOx
GEOS-Chem Model Simulations (4°x5°)
IPCC
Anthrop. NOx emissions
scenario
(2030 vs. present)
Global
U.S.
Methane
emissions
(2030 vs. present)
A1
+80%
-20%
+30%
CH4 links air quality
& climate via
background O3
B1
-5%
-50%
+12%
Fiore et al., GRL, 2002
Response of Global Surface Ozone to 50% decrease in global methane
emissions (actually changing uniform concentration from 1700 to 1000 ppbv)
• Ozone decreases by 1-6 ppb
• ~3 ppb over land in US summer
** ~60% of reduction in 10 yr; ~80% in 20 yr.
Impacts of O3 Precursor Reductions on
U.S. Summer Afternoon Surface O3 Frequency Distributions
GEOS-Chem Model Simulations (4°x5°)
West & Fiore, ES&T, 2005
Tropospheric ozone response to anthropogenic methane
emission changes is fairly linear
MOZART-2 (this work)
TM3 [Dentener et al., ACPD, 2005]
GISS [Shindell et al., GRL, 2005
X GEOS-CHEM [Fiore et al., GRL, 2002]
IPCC TAR [Prather et al., 2001]
How Much Methane Can Be Reduced?
Ozone reduction (ppb)
Cost-saving
reductions
0.7
10% of anthrop.
emissions
North America
Rest of Annex I
Rest of World
1.4
<$10 / ton
CO2 eq.
20% of anthrop.
emissions
All identified
reductions
00
1.9
20
40
60
80
100
120
20
40
60
80
100 -1
120
Methane
Methane reduction
reductionpotential
potential(Mton
(MtonCH
CH4 4yryr)-1)
IEA [2003] for 5 industrial sectors
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
Ozone Abatement Strategies Evolve as our
Understanding of the Ozone Problem Advances
O3 smog recognized
as an URBAN problem:
Los Angeles,
Haagen-Smit identifies
chemical mechanism
1950s
Abatement Strategy:
NMVOCs
Smog considered
REGIONAL problem;
role of biogenic
VOCs discovered
A GLOBAL perspective:
role of intercontinental
transport, background
Present
1980s
+ NOx
+ CH4??
Addressing the CH4-O3 air quality-climate linkage
Methane controls are receiving attention as a means to
simultaneously address climate and global air pollution
[EMEP/CCC report 1/2005]
1. Does CH4 source location
influence the O3 response?
1790
2. What is driving recent trends
in atmospheric CH4 ?
 Sources?
 Sinks?
1780
1770
1760
1750
1740
1730
1720
1710
Observed Global Mean CH4 (ppb)
1990
1992
1994
1996
1998
2000
2002
2004
Methane Control Simulations in MOZART-2:
30% Decrease in Global Anthropogenic CH4 Emissions
0
0
Change in methane (ppb)
Global surface CH4 conc. (ppb)
1800
BASE CASE
1650
1600
1550
-30% anthrop. emis.
1500
10
15
20
25
-150
-200
-250
-300
-350
1450
-400
1400
Year
1350
0
1300
1
0
5
10
15
20
25
30
-2
-4
Tg Ozone
Tg
Year
 Approaching steady-state after 30 years
-6
 Does O3 impact depend on source location?
-8
(1) global -30% anthrop. emissions
-10
(2) zero Asian emissions (=30% global)
30
Change in global
surface CH4 conc.
from 30% decrease
in anthrop. emis.
-100
ppb
Surface Methane (ppb)
1750
1700
5
-50
6
11
16
21
26
Decrease in
Tropospheric
O3 Burden
-12
Year
CLIMATE IMPACTS: Change in July 2000 Trop. O3 Columns
(to 200 hPa)
30% decrease in global anthrop.
CH4 emissions
-34
-27
-20
No Asia – (30% global decrease)
Zero CH4 emissions from Asia
(= 30% decrease in global anthrop.)
-14
Dobson Units
-7 mW m-2 (Radiative Forcing)
Tropospheric O3 column response is
independent of CH4 emission location
except for small (~10%) local changes
-5.1
-3.4
-1.7
DU
-0.7 +0.7 mW m-2
U.S. Surface Afternoon Ozone Response in Summer
also independent of methane emission location
MEAN DIFFERENCE
NO ASIAN ANTHROP. CH4
MAX DIFFERENCE
(Composite max daily
afternoon mean JJA)
GLOBAL 30% DECREASE IN ANTHROP. CH4
Stronger sensitivity in NOx-saturated regions (Los Angeles),
partially due to local ozone production from methane
Observed trend in Surface CH4 (ppb) 1990-2004
Global Mean CH4 (ppb)
Hypotheses for leveling off
discussed in the literature:
1790
1780
1. Approach to steady-state
1770
1760
GMD Network
1750
1740
1730
1720
2. Source Changes
Anthropogenic
Wetlands
Biomass burning
3. Transport
1710
1990
1992
1994
1996
1998
2000
2002
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
4. Sink (OH)
Humidity
Temperature
OH precursor emissions
overhead O3 columns
How does BASE CASE Model compare with GMD observations?
Global Mean Surface Methane (ppb)
Model with constant emissions largely captures
observed trend in CH4 during the 1990s
1790
OBSERVED
1780
1770
BASE CASE MODEL
1760
1750
Captures flattening post-1998
but underestimates abundance
Emissions problem?
1740
1730
1720
1710
1990
1992
1994
1996
1998
2000
2002
2004
Possible explanations for observed behavior:
(1) Source changes
(2) Meteorologically-driven changes in CH4 lifetime
(3) Approach to steady-state with constant lifetime
Bias and Correlation vs. GMD Surface CH4: 1990-2004
Mean Bias (ppb)
r2
BASE
BASE simulation with constant emissions:
 Overestimates interhemispheric gradient
 Correlates poorly at high northern latitudes
Biomass Burning
Ruminants
Estimates for Changing
Methane Sources in the 1990s
Rice
Biogenic
Wastewater
Inter-annually varying wetland emissions
Biomass Burning
Landfills
1990-1998 from Wang et al. [2004]
Ruminants
Energy
(Tg CH4 yr-1); distribution changes
Rice
Biogenic adjusted to maintain
270
constant total source
Wastewater
260
Landfills
547
Energy
1995
500v3.2 2000 v3.2
250
Tg CH4 yr-1
240
Biogenic
230
Biomass Burning
Ruminants
220
Rice
210
Wastewater
Landfills
200
Energy
1990
1995
400
300
200
100
2000
Apply climatological mean
(224 Tg yr-1) post-1998
0
1990 v2.0 1990 v3.2 1995 v3.2 2000 v3.2
BASE
ANTH
EDGAR anthropogenic inventory
ANTH + BIO
2005
Bias & Correlation vs. GMD CH4 observations: 1990-2004
Mean Bias (ppb)
1790
1780
1770
1760
1750
OBS
BASE
ANTH
1740
1730
1720
1710
1990
1992
1994
1996
1998
2000
2002
2004
ANTH simulation with time-varying
EDGAR 3.2 emissions:
 Improves abundance post-1998
 Interhemispheric gradient too high
 Poor correlation at high N latitudes
r2
Bias & Correlation vs. GMD CH4 observations: 1990-2004
Mean Bias (ppb)
1790
1780
1770
1760
1750
OBS
BASE
ANTH
ANTH+BIO
1740
1730
1720
1710
1990
1995
2000
ANTH+BIO simulation with timevarying EDGAR 3.2 + wetland
emissions improves:
 Global mean surface conc.
 Interhemispheric gradient
 Correlation at high N latitudes
2005
r2
S
Latitude
N
OBS (GMD)
BASE
ANTH
ANTH+BIO
Model with
BIO wetlands
improves:
Methane Concentration (nmol/mol = ppb)
1900
1850
1800
Alert (82.4N,62.5W) 1)high N latitude
seasonal cycle
1840
1820
1800
1780
1760
1740
2)trend
Midway (28.2N,177.4W)
3)low bias
at S Pole,
especially
post-1998
1800
1750
1700
Mahe Island (4.7S,55.2E)
1740
1720
1700
1680
1660
1640
South Pole (89.9S,24.8W)
1990
1995
2000
2005
Model
captures
distinct
seasonal
cycles at
GMD
stations
Time-Varying Emissions: Summary
1790
1780
1770
Annual mean CH4 in the
“time-varying ANTH+BIO”
simulation best captures
observed distribution
1760
1750
OBS
BASE
ANTH
ANTH+BIO
1740
1730
1720
1710
1990
1995
2000
2005
Next: Focus on Sinks
-- Examine with BASE model (constant emissions)
-- Recycle NCEP winds from 2004 “steady-state”
Methane rises again when 1990-1997 winds
are applied to “steady-state” 2004 concentrations
Area-weighted Global Mean Methane
Concentrations
Area-weighted
global mean CH4 concentrations in
BASE simulation (constant emissions)
1780
1770
1760
1750
1740
 Recycled NCEP 1990-2004
1730
1720
1710
1990
1995
2000
2005
2010
2015
Year (NCEP winds recycled such that 2005 = 1990 met fields)
 Meteorological
drivers for observed trend
 Not just simple approach to steady-state
2020
How does meteorology affect the CH4 lifetime?
10.7
CH4 Lifetime vs. Tropospheric OH
Candidate Processes:
10.6
10.5
Rapid transport to sink regions
10.4
t=
10.3
10.2
10.1
10
 Recycled NCEP
9.9
1990
1995
2000
2005
2010
2015
2020
Temperature
Lifetime Correlates Strongly With Lower Tropospheric
OH
and
Temperature
10.7
r2 = 0.69
10.5
10.4
10.3
10.2
10.1
10
1.30
1.32
1.34
105 molecules cm-3
1.36
Lifetime vs. Trop OH
10.7
10.6
9.9
1.28
[CH 4 ]
k[OH][CH 4 ]
10.6
r2 = 0.65
10.5
10.4
10.3
10.2
10.1
1.38
10
9.9
273.2
273.4
273.6
273.8
274
K
Lower Tropospheric
Temperature
274.2
Humidity
Lightning NOx
Photolysis
Methane Distribution and Trends: Climate and Air Quality Impacts
•
20% anthrop. CH4 emissions can be reduced at low cost
•
Ozone response largely independent of CH4 source location
•
30% decreases in anthrop. CH4 reduces radiative forcing by 0.2
Wm-2 and JJA U.S. surface O3 by 1-4 ppbv
1790
1780
Hypotheses for leveling off:
Global Mean CH4 (ppb)
1770
1760
1750
1740
1730
1720
1710
1990
1992
1994
1996
1998
2000
2002
2004
1. Approach to steady-state
 not the whole story
2. Source Changes
 improve simulated abundances
but not driving trend
3. Transport Meteorology major driver;
further work needed to
4. Sink (OH) isolate cause
Potential for strong climate feedbacks
Q: How will future global change influence atmospheric CH4?
Potential for complex biosphere-atmosphere interactions
CH4 + OH
BVOC
…products
NOx
Soil