Transcript Recent and future trends in atmospheric methane: Connecting global chemistry, climate and ozone pollution Arlene M.

Recent and future trends
in atmospheric methane:
Connecting global chemistry,
climate and ozone pollution
Arlene M. Fiore
([email protected])
Acknowledgments:
Larry Horowitz, Chip Levy (NOAA/GFDL)
Jason West, Vaishali Naik (Princeton University)
Ellen Baum, Joe Chaisson (Clean Air Task Force)
Funding from Luce Foundation via Clean Air Task Force
Berkeley Atmospheric Sciences Symposium, September 29, 2006
Historical increase in atmospheric methane and ozone
Variations of CH4 Concentration (ppb)
Over the Past 1000 years
[Etheridge et al., 1998]
Ozone at European mountain sites
1870-1990 [Marenco et al., 1994]
1600
1400
1200
1000
800
1000
1500
Year
2000
Radiative forcing of climate, 1750-Present:
Important contributions from methane and ozone
IPCC [2001]
Level of scientific understanding
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
IPCC [2001] scenarios project future growth
Projections of future CH4 emissions
(Tg CH4) to 2100
Change in 10-model mean
surface O3
2100 SRES A2 - 2000
Attributed mainly to increases
in methane and NOx
[Prather et al., 2003]
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
Smog as REGIONAL
problem; role of NOx
and biogenic VOCs
recognized
1950s
Abatement Strategy:
NMVOCs
A GLOBAL perspective:
role of intercontinental
transport, background
Present
1980s
+ NOx
+ CH4??
“Methane (and CO) emission control is an effective way of simultaneously
meeting air quality standards and abating global warming”
--- EMEP/CCC-Report 1/2005
Impacts of O3 precursor reductions on
U.S. summer afternoon surface O3 frequency distributions
GEOS-Chem Model Simulations (4°x5°)
NOx controls
strongly decrease
the highest O3
(regional pollution
episodes)
CH4 controls
affect the entire
O3 distribution
similarly
(background)
Results add linearly when both methane and NOx are reduced
Fiore et al., 2002; West & Fiore, ES&T, 2005
Rising background O3 has implications
for attaining air quality standards
Surface O3 background appears to be rising
[e.g. Lin et al., 2000; Jaffe et al., 2003, 2005;
Vingarzan, 2004; EMEP/CCC-Report 1/2005 ]
Pre-industrial
background
20
Europe
seasonal
40
Current background
Future
background?
WHO/Europe
8-hr average
60
U.S. 8-hr
average
80
100
O3 (ppbv)
Methane trends and linkages with
chemistry, climate, and ozone pollution
1) Methane Trends from 1990 to 2004
 Are emission inventories consistent with observed CH4 trends?
 Role of changing sources?
 Role of changing sinks?
2) Climate and air quality benefits from CH4 controls
 Characterize the ozone response to CH4 control
 Compare with traditional controls on NOx, NMVOC
 Incorporate methane controls into a future emission scenario
Research Tool:
MOZART-2 Global Chemical
Transport Model [Horowitz et al., 2003]
NCEP, 1.9°x1.9°, 28 vertical levels
 Fully represent methane-OH relationship
 Test directly with observations
3D model structure
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
Clathrates?
Melting permafrost?
PLANTS?
BIOMASS BURNING
+ BIOFUEL
ANIMALS
30
WETLANDS
90
180
60-240 Keppler et al., 2006
85 Sanderson et al., 2006
10-60 Kirschbaum et al., 2006
0-46 Ferretti et al., 2006
GLOBAL METHANE
SOURCES
(Tg CH4 yr-1)
TERMITES RICE 40
20
COAL
30
LANDFILLS +
WASTEWATER
50
GAS + OIL
60
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
NOAA GMD Network
1750
1740
1730
1720
2. Source Changes
Anthropogenic
Wetlands/plants
(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 (CH4+OH)
Humidity
Temperature
OH precursor emissions
overhead O3 columns
Can the model capture the observed trend (and be used for attribution)?
BASE simulation
EDGAR 2.0 emissions held constant
1790
1780
Global Mean Surface Methane (ppb)
OBSERVED
MOZART-2
1770
1760
Mean Bias (ppb)
Bias and correlation vs. observed surface CH4: 1990-2004
Overestimates
interhemispheric
gradient
1750
1740
1730
1720
1990
1992
1994
1996
1998
2000
2002
2004
Overestimates 1990-1997
but matches trend
Captures flattening post1998 but underestimates
abundance
r2
1710
Correlates poorly
at high N latitudes
S
Latitude
N
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); different distribution
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
Global Mean Surface Methane (ppb)
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
S
Latitude
N
Bias & Correlation vs. GMD CH4 observations: 1990-2004
Global Mean Surface Methane (ppb)
Mean Bias (ppb)
1790
1780
1770
1760
1750
OBS
BASE
ANTH
ANTH+BIO
1740
1730
1720
1710
1990
1995
2000
2005
ANTH+BIO simulation with timevarying EDGAR 3.2 + wetland
emissions improves:
 Global mean surface conc.
 Interhemispheric gradient
 Correlation at high N latitudes
Fiore et al., GRL, 2006
r2
S
Latitude
N
How does meteorology influence methane abundances?
Why does BASE run with constant emissions level off post-1998?
 Examine sink
CH4 Lifetime (t) against Tropospheric OH
t=
[CH 4 ]
k[OH][CH 4 ]
Dt
Temperature
(88% of CH4 loss
is below 500 hPa )
Humidity
Photolysis
Lightning NOx
Dt = 0.17 yr = 1.6%)
What drives the change in
methane lifetime in the model?
Small increases in temperature and OH
shorten the methane lifetime against tropospheric OH
DtOH
0.18
Deconstruct Dt (-0.17 years)
from 1991-1995 to 2000-2004
into individual contributions by
varying OH and temperature
separately
0.16
0.14
0.12
0.1
0.08
+
0.06
=
0.04
0.02
Lightning NOx
3.4
Global Lightning NOx (TgN yr-1)
0
DT(+0.3K)
climT
DOH(+1.2%)
climOH
BASE
BASE
3.2
LNOx (TgN/y)
3
2.8
An increase in lightning NOx drives the
OH increase in the model
2.6
2.4
2.2
But lightning NOx is highly parameterized
…how robust is this result?
2
1.8
1990
1992
1994
1996
1998
Year
2000
2002
2004
Work in progress:
Additional evidence for a global lightning NOx increase?
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)
Lightning
NOx NOx
change,
1991-95
to 2000-04
Lightning
change,
1991-95
to 2000-04
20% 20%
Lightning NOx % change (91-95 to 00-04)
RAS Donner
MOZART
18% 18%
More physically-based lightning
NOx scheme [Petersen et al., 2005]
16% 16%
Evidence from observations?
14% 14%
MOZART-2
MOZART-2
10% 10%
AM2 AM2
% change
12% 12%
8%
8%
6%
6%
4%
4%
2%
2%
0%
0%
AM2-D
AM2-D
NCEP(nudged)
free-running GCM
Lightning NOx increase robust;
magnitude depends on meteorology
c/o L.W. Horowitz
LIS/OTD
Flash counts
Magnetic field variations
in the lower ELF range
[e.g. Williams, 1992;
Füllekrug and FraserSmith, 1997; Price, 2000] Negev Desert
Station, Israel
Recap: Methane trends 1990-2004
Global Mean Surface Methane (ppb)
1790
1780
1770
1760
Available emissions estimates
for the past decade are fairly
consistent with CH4 observations
OBS
ANTH+BIO
BASE
ANTH
Dt decreases by 1.6% in BASE
1750
from 1991-1995 to 2000-2004 due to
higher temp. (+0.3K) and OH (+1.2%);
OH rise from enhanced lightning NOx
1740
1730
1720
1710
1990
1995
2000
2005
NEXT: Climate and air quality benefits from CH4 controls
1) Magnitude, spatial variability, linearity
2) Comparison with traditional O3 control strategies
3) Future scenarios
Characterizing the methane-ozone relationship
with idealized model simulations
Reduce global anthropogenic
CH emissions by 30%
Surface Methane
Tropospheric O34burden
0
0
-50
D Surface
Methane
Abundance
(ppb)
-2
-100
-4
-150
-200
-6
-250
-8
-300
DTropospheric
O3 Burden
(Tg)
-10
-350
-400
-12
1
6
11
16
21
26
31
Simulation Year
Model approaches a new steady-state after 30 years of simulation
Is the O3 response sensitive to the location of CH4 emission controls?
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
Target cheapest controls worldwide
-5.1
-3.4
-1.7
DU
-0.7 +0.7 mW m-2
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
Tropospheric O3 responds approximately linearly to
anthropogenic CH4 emission changes across models
MOZART-2 [West et al., PNAS 2006; this work]
TM3 [Dentener et al., ACP, 2005]
GISS [Shindell et al., GRL, 2005]
X 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 surface O3
How much methane can be reduced?
Ozone reduction (ppb)
Cost-saving
reductions
0.7
North America
Rest of Annex I
Rest of World
(industrialized nations)
1.4
<$10 / ton
CO2 eq.
All identified
reductions
00
1.9
10% of anth.
emissions
20% of anth.
emissions
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
Impacts of O3 precursor reductions on global surface O3
Steady-state change in 8-hr daily maximum surface O3
averaged over 3-month “O3 season”
from 20% reductions in global anthropogenic emissions
NOx
NMVOC
ppbv
CO
CH4
MOZART-2 model (2.8° x 2.8°)
ppbv
West et
al., submitted
Double dividend of methane controls:
Improved 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)
CLIMATE:
Radiative Forcing (W m-2)
NOx
 OH 
CH4
20% 20% 20% 20%
20% 20% 20% 20%
anth. anth. anth. anth.
anth. anth. anth. anth.
NMVOC CO
NOx
NMVOC CO
CH4 NOx
CH4
Steady-state results from MOZART-2
West et al.,submitted
Will methane emissions increase in the future?
Anthropogenic CH4 emissions (Tg yr-1)
Dentener et al., ACP, 2005
A2
B2
MFR
Current
Legislation
(CLE)
Scenario
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]
 Our approach: use CLE as a baseline scenario & apply methane controls
Policy-relevant methane control scenarios to 2030
Anthropogenic CH4 emissions (Tg yr-1)
500
+29% from 2005 to 2030 under CLE
450
400
CH4 (Tg
350
2030 decrease relative to CLE:
300
250
200
150
100
50
0
2000
CLE
A: -75 Tg (18% of 2030 anthrop. CH4 emis.)
Scen A
B: -125 Tg (29%)
Scen B
Scen C
c/o J.J. West
2005
2010
2015
2020
2025
C: -180 Tg (42%)
2030
Transient, full-chemistry simulations in MOZART-2;
2000-2004 NCEP meteorology, recycled for 2005-2030
Other O3 precursor emissions follow the 2005-2030 CLE baseline:
Anthrop. NOx emissions increase by 5.3 Tg N (+19%)
Anthrop. CO emissions decrease by 44 Tg CO (-10%)
Preliminary results:
Impacts on climate and global surface ozone
Radiative Forcing (W m-2)
2005 to 2030
+0.16 Net Forcing
30.5
+0.08
0.00
-0.08
ppb
30
GlobalAnnual
Annual Mean
Surface Surface
Ozone
Global
Mean
O3
CLE A B CLE
C 2030
29.5
29
28.5
28
2005
2010
2015
2020
Year
CLE
A
B
C
Scenario C stabilizes
despite 5 Tg N
increase in anth. NOx
Cost-benefit analysis in progress...
2025
2030
Regional control efforts (even under optimistic scenarios)
may be offset by increases in hemispheric ozone pollution
By 2030 under the CLE scenario,
“the benefit of European emission control measures is…
significantly counterbalanced by increasing global O3 levels…”
[Szopa et al., GRL, 2006]
U.S. air quality degrades despite domestic emissions controls (A1 2030)
1995 Base case
2030 A1
IPCC 2030
Scenario
A1
Anthrop. NOx emis.
Global
U.S.
+80%
-20%
Methane
emis.
+30%
GEOS-Chem Model (4°x5°)
[Fiore et al., GRL, 2002]
longer O3 season
International approach to ozone abatement?
TF HTAP multi-model assessment of
intercontinental source-receptor relationships
www.htap.org
Co-Chairs: Terry Keating (U.S. EPA), Andre Zuber (EC)
Intercontinental Source-Receptor Regions
http://aqm.jrc.it/HTAP
Experiment Set 1 (~20 models):
Decrease precursor emissions by 20% in source regions
Estimate pollutant response over receptor regions
 Inform 2007 review of CLRTAP Gothenburg Protocol
Methane trends: Connecting climate and O3 chemistry
Methane (ppb)
1790
1780
1770
1760
OBS
BASE
ANTH
ANTH+BIO
1750
1740
1730
1720
1710
1990
0.18
1995
2000
METHANE TRENDS FROM 1990 TO 2004
• Simulation with time-varying emissions and meteorology
best captures observed CH4 distribution
2005
• Model trend driven by increasing T, OH
DtOH 91-95 to 01-04
0.16
• Trends in global lightning activity?
 Potential for climate feedbacks (on sources and sinks)
0.14
0.12
0.1
0.08
0.06
+
0.04
0.02
0
DT
=
DOH
climT
climOH
BASE
Ozone reduction (ppb)
BASE
North America
Rest of Annex I
Rest of World
Cost-saving
reductions
• Independent of reduction location
Target cheapest controls worldwide
<$10 / ton
CO2 eq.
All identified
reductions
0
20
40
60
80
100
CLIMATE AND AIR QUALITY BENEFITS FROM CH4 CONTROL
120
• Reduces climate forcing and surface O3
Methane reduction potential (Mton CH 4 yr-1)
Methane Surface Concentration
Global mean surface CH4
2100
• Rising hemispheric background O3 may offset domestic
efforts to reduce pollution
Opportunity for international air quality management
2000
ppb
1900
1800
1700
1600
1500
2005
• Complementary to NOx, NMVOC controls
2010
2015
2020
Year
2025
2030