Source vs. Sink Contributions to Atmospheric Methane Trends: 1990-2004
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Transcript of Source vs. Sink Contributions to Atmospheric Methane Trends: 1990-2004
Source vs. Sink Contributions Source vs. Sink Contributions to Atmospheric Methane to Atmospheric Methane
Trends: 1990-2004Trends: 1990-2004
Arlene M. Fiore
Larry Horowitz (NOAA/GFDL)Ed Dlugokencky (NOAA/GMD)
Jason West (Princeton)
Informal Seminar at NOAA GMDJanuary 24, 2006
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]
ANIMALS90
LANDFILLS +WASTEWATER
50GAS + OIL60
COAL30RICE 40TERMITES
20
WETLANDS180
BIOMASS BURNING + BIOFUEL 30
GLOBAL METHANESOURCES
(Tg CH4 yr-1)
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
GMD Network
Global Mean CH4 (ppb)Hypotheses for leveling offdiscussed in the literature:
1. Approach to steady-state 2. Source Changes Anthropogenic
WetlandsBiomass burning
3. Transport
4. Sink (OH) Humidity Temperature OH precursor emissions overhead O3 columns
How does a 3-D forward model compare with GMD observations?
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1990 1992 1994 1996 1998 2000 2002 2004
Global Mean Surface Methane (ppb)
OBSERVED
Model with constant emissions largely captures
observed trend in CH4 during the 1990s
Captures flattening post-1998 but underestimates abundance
Emissions problem?
MOZART-2 [Horowitz et al., 2003]• NCEP• 1.9°x1.9°• 28 -levels• EDGAR v.2.0 emissions
• CH4 EDGAR
emissions for 1990s
Bias and Correlation vs. GMD Surface CH4: 1990-2004
BASE simulation with constant emissions: Overestimates interhemispheric gradient Correlates poorly at high northern latitudes
BASE
Mean Bias (ppb) r2
Estimates for Changing Methane Sources in the 1990s
547
Tg
CH
4 yr
-1
EDGAR anthropogenic inventory
Biogenic adjusted to maintainconstant total source
BASE ANTH
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Inter-annually varying wetland emissions1990-1998 from Wang et al. [2004](Tg CH4 yr-1); distribution changes
Apply climatological mean (224 Tg yr-1) post-1998
ANTH + BIO
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1990 1992 1994 1996 1998 2000 2002 2004
OBSBASEANTH
Mea
n B
ias
(pp
b)
r2
Bias & Correlation vs. GMD CH4 observations: 1990-2004
ANTH simulation with time-varying EDGAR 3.2 emissions: Improves abundance post-1998 Interhemispheric gradient too high Poor correlation at high N latitudes
Mea
n B
ias
(pp
b)
ANTH+BIO simulation with time-varying EDGAR 3.2 + wetland emissions improves: Global mean surface conc. Interhemispheric gradient Correlation at high N latitudes
Bias & Correlation vs. GMD CH4 observations: 1990-2004
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1990 1995 2000 2005
OBSBASEANTHANTH+BIO
r2
S Latitude N
Met
han
e C
on
cen
trat
ion
(n
mo
l/m
ol
= p
pb
)OBS (GMD) BASE ANTH ANTH+BIO
Alert (82.4N,62.5W)
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Mahe Island (4.7S,55.2E)
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1700
Midway (28.2N,177.4W)
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South Pole (89.9S,24.8W)
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Model capturesdistinct seasonalcycles at GMD stations
Model withBIO wetlandsimproves:
1)high N latitudeseasonal cycle
2)trend
3)low biasat S Pole,especiallypost-1998
Time-Varying Emissions: Summary
Next: Focus on Sinks-- Examine with BASE model (constant
emissions)-- Recycle NCEP winds from 2004 “steady-
state”
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OBSBASEANTHANTH+BIO
Annual mean CH4 in the “time-varying ANTH+BIO” simulation best captures observed distribution
Methane rises again when 1990-1997 winds are applied to “steady-state” 2004 concentrations
Recycled NCEP 1990-2004
Meteorological drivers for observed trend Not just simple approach to steady-state
Area-weighted global mean CH4 concentrations in BASE simulation (constant emissions)
9.9
10
10.1
10.2
10.3
10.4
10.5
273.2 273.4 273.6 273.8 274 274.2
Global mean lower trop Temp 1991-2004
Lif
eti
me
ag
ain
st
tro
p O
H
r2 = 0.83
How does meteorology affect the CH4 lifetime?
]CH][OH[
]CH[
4
4
k=
9.9
10
10.1
10.2
10.3
10.4
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10.6
10.7
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Recycled NCEP
CH4 Lifetime against Tropospheric OH
105 molecules cm-3
TemperatureHumidityLightning NOx
Photolysis
Rapid transport to sink regions
Candidate Processes:
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10.1
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1.31E+05 1.32E+05 1.32E+05 1.33E+05 1.33E+05 1.34E+05 1.34E+05 1.35E+05
Global Mean Lower Trop OH 1991-2004
Life
time
agai
nst T
rop
OH
Lifetime Correlates Strongly With Lower Tropospheric OH and Temperature
r2 = 0.51
r2 = 0.89 vs. OHif 1998 neglected(0.80 for Temp)
Deconstruct (-0.17 years) from 1991-1995 to 2000-2004 into individual contributions by varying OH and temperature
separately
0
0.02
0.04
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0.08
0.1
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0.18
climT climOH BASET(+0.3K) OH(+1.4%) BASE
+ =
OH increases in the model by 1.4% due to a 0.3 Tg N yr-1 increase in lightning NOx emissions
Large uncertainties in magnitude (and trend) of lightning NOx
emissions in the real atmosphere
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Methane Distribution and Trends: Conclusions
Global Mean CH4 (ppb)
Potential for strong climate feedbacks
OBSERVED
CH4 decreases by ~2% from 1991-1995 to 2000-2004 due to warmer temperatures (35%) and higher OH (65%), resulting from a 10% increase in lightning NOx emissions
BASE (constant emissions) captures observed rate of increase 1990-1997 and leveling off post-1998
ANTH improves modeled CH4 post-1998
Wetland emissions in ANTH+BIO best match observed seasonality, inter-hemispheric gradient and global trend
Q: How will future global change influence atmospheric CH4?Potential for complex biosphere-atmosphere interactions…
can be studied with GFDL earth system model
CH4 + OH …products
Soil
BVOC NOx
Higher in a warmer climate?