renewed increase in atmospheric methane: review on … · 2019. 7. 8. · 14 │ ralf sussmann:...
TRANSCRIPT
KIT – The Research University in the Helmholtz Association
INSTITUTE OF METEOROLOGY AND CLIMATE RESEARCH, ATMOSPHERIC ENVIRONMENTAL RESEARCH, IMK-IFU
REGIONAL CLIMATE SYSTEMS – Atmospheric Variability and Trends
www.imk-ifu.kit.edu
RENEWED INCREASE IN ATMOSPHERIC METHANE:
REVIEW ON RECONCILING SOURCE ATTRIBUTIONS
Ralf Sussmann
2 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Global Methane Budget 2003-2012
3 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Renewed methane increase after 2006: Solar FTIR
Year Year
• Zugspitze (47 °N) measurement (XCH4) representative for NH (30-90 °N)
• Lauder (45 °S) measurement (XCH4) representative for SH (30-90 °S)
Sussmann, Forster, Rettinger, Bousquet, Atmos. Chem. Phys., 2012
update: P. Hausmann, 2014
4 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Renewed methane increase after 2006: Solar FTIR
Year Year
• Zugspitze (47 °N) measurement (XCH4) representative for NH (30-90 °N)
• Lauder (45 °S) measurement (XCH4) representative for SH (30-90 °S)
Sussmann, Forster, Rettinger, Bousquet, Atmos. Chem. Phys., 2012
update: P. Hausmann, 2014
1ppb
CH4 Emission (Tg/yr) Sink (reaction with OH)
CH4 Atmospheric
concentration (ppb)
1 ppb ← 3 Tg CH4
CH4-Trend after 2006 ~8 ppb/yr
equivalent to global net CH4 emissions increase of
~25 Tg/yr wrt to an annual source of 560 Tg/yr
5 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Inman, Nature, 2014
Why quantify oil & gas contribution to
atmospheric methane increase?
• oil & gas production increased after 2006:
6 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Methane sources: what does ethane tell us?
Ethane (C2H6) shares major source with methane:
fossil fuel production / distribution
No significant
biogenic sources
Valuable tracer for thermogenic methane (oil & gas contrib.)
7 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Ethane-based CH4-source
attribution: oil & gas contrib.
Scenario MER Oil & Gas
Contribution
Oil & Gas 3.3–7.6 39–160 %
source sink source sink
NH SH
ΔEC2H6, oil & gas × MER
ΔECH4
C =
Sussmann, Hausmann, Smale, Atmos. Chem. Phys., 2016
8 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Ethane-based CH4-source
attribution: oil & gas contrib.
Scenario MER Oil & Gas
Contribution
Oil & Gas 3.3–7.6 39–160 %
source sink source sink
NH SH
ΔEC2H6, oil & gas × MER
ΔECH4
C =
Sussmann, Hausmann, Smale, Atmos. Chem. Phys., 2016
25 Tg CH4/yr total emissions increase after 2006
10 - 25 Tg CH4/yr emissions increase from oil & gas
originates from northern hemisphere
from which country?
9 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Global methane growth: US contribution
Turner et al. (Geophys. Res. Lett., 2016):
US methane emissions account for 30-60% of the global growth
of atmospheric methane in the past decade.
10 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Isotopic CH4-source attribution: biogenic
sources are isotopically depleted
Schaefer et al., Science, 2016:
• used isotopic in situ measurements
• found biogenic increases of ~21 Tg/yr
Together with the Hausmann et al. (2016)
estimate of 10-25 Tg/yr increase from
fossil fuels, this exceeds the total
increase of 25 Tg/yr!
11 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
CH4-source attribution via CO: tracer for
biomass burning emissions
Worden et al., Nature,
2017:
satellite based CO
emissions from biomass
burning
+
CH4/CO fire emisson
ratios
CH4 emissions from
biomass burning
• biomass burning emissions of methane decreased by 3.7 (±1.4) Tg CH4 per year
from the 2001–2007 to the 2008–2014 time periods
• nearly twice the decrease expected from burnt area prior estimates
12 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
• Because biomass burning emissions are isotopically heavier than those from fossil
fuel or biogenic CH4 sources, the larger-than-expected decrease in fire emissions
requires a substantial re-balancing of sources:
Fossil fuel contributions have to become an increasingly larger contribution to
the overall increase in methane to account for larger decreases in biomass
burning and in order to also balance the isotopic budget.
• This tendency is further enhanced: Recent updates for the isotope signatures have
profoundly changed the global partitioning between source categories, resulting in
a larger fossil fuel contribution.
Source attribution via CO and 13CH4: reduced
biomass burning & increased fossil fuel emissions
Worden et al., Nature, 2017
13 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
• Because biomass burning emissions are isotopically heavier than those from fossil
fuel or biogenic CH4 sources, the larger-than-expected decrease in fire emissions
requires a substantial re-balancing of sources:
Fossil fuel contributions have to become an increasingly larger contribution to
the overall increase in methane to account for larger decreases in biomass
burning and in order to also balance the isotopic budget.
• This tendency is further enhanced: Recent updates for the isotope signatures have
profoundly changed the global partitioning between source categories, resulting in
a larger fossil fuel contribution.
lighter heavier heavier
Update of 13CH4 signatures: even more reduced
biomass burning & increased fossil fuel emissions
lighter lighter heavier
14 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Conclusions
• Factor 2 stronger decrease of biomass burning emissions (Worden et al., 2017)
&
• revisions to the isotopic composition of methane sources (Schwietzke et al.,
2016)
lead to a revised post-2007 atmospheric methane budget (Worden et al.,
2017):
• fossil fuel CH4 emissions increase of 12–19 Tg/yr,
• biogenic CH4 emissions increase of 12–16 Tg/yr
reconcile the previously conflicting findings, where
• ethane/methane measurements (Hausmann, Sussmann, Smale, 2016)
indicated a fossil fuel CH4 emissions increase of 10-25 Tg/yr,
• while isotopic evidence (Schaefer et al., 2016)
indicated a biogenic CH4 emissions increase of ~21 Tg/yr.
Acknowledgments: Funding by ESA, EC, and the Helmholtz Association
15 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
ADDITIONAL SLIDES
16 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions Ralf Sussmann - Zugspitze &
Schneefernerhaus
Schaefer et al., Science, March 2016 Hausmann et al., ACP May 2016
Turner et al., PNAS, Dec 2016
39 %
Hausmann study based on ethane
proxy: more selective than 13 CH4 .
Confirmed by
Helmig et al., Nat. Geosci., Jun 2016
Cowern et al., Nature, 2017, subm.
Unrealistic assumption
by Schaefer et al.:
13 CH4 (ff) = -37 ‰
13 CH4 (nf) = -60 ‰
17 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Renewed methane increase –
Optimized emission scenarios
Scenario MER Oil & Gas
Contribution
Oil & Gas 3.3–7.6 39–160 %
Oil (limit) 1.7–3.3 18–72 %
Gas (limit) 7.6–12.1 73–280 %
source sink source sink
NH SH
ΔEC2H6, oil & gas × MER
ΔECH4
C =
18 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Use ethane as a proxy for thermogenic methane
Year Year
Time scales
• life time methane 9 years
• interhemispheric mixing 1 year
• life time ethane 3 months
• hemispheric mixing 1 month
19 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Leakage threshold value of 3.2 % for immediate
climate benefit
based on Alvarez et al. (2012)
20 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Increase of atmospheric methane concentration
– attribution to changes in sources/sinks?
• Possibly decreasing (OH) sink (?)
• And/Or increasing CH4 emissions:
biogenic? thermogenic? pyrogenic? natural,
anthropogenic?
21 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Long-term trends – correlation
Correlation &
Lin. regression
1999 – 2006 2007 – 2014
Zugspitze Lauder Zugspitze Lauder
Sign. correlated? no no yes no
Regression slope -0.02 % 0.05 % 0.31 % -0.04 %
Uncertainty (±2σ) ± 0.16 % ± 0.08 % ± 0.07 % ± 0.04 %
Well-stirred reactor model
Emission ratio EMRsrc
EMRsrc = EMRbg × kC2H6 / kCH4
= 12 – 19 %
EMR for oil & gas sources
EMRo&g = 1 – 25 %
22 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Schneising et al. (2014):
Colors: methane (2009-11) minus
(2006-08)
• leakages of 10.1 % 7.3 % and 9.1 % 6.2 %
• exceed the threshold value of 3.2 % required for immediate climate
benefit (Alvarez et al., 2012)
Fracking leakages
23 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Two-box model – setup (1)
Ethane column (1016 cm-2)
Xiao et al.,
2008
Methane column (ppb)
Saito et al., 2012
Zugspitze (47° N, 11° E)
Lauder (45° S, 170° E)
24 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Two-box model – setup (2)
source sink source sink
XN XS
𝑑𝑋N
𝑑𝑡= 𝐸N −
𝑋N
𝜆−
𝑋N −𝑋S
𝜏ex
𝑑𝑋S
𝑑𝑡= 𝐸S −
𝑋S
𝜆+
𝑋N −𝑋S
𝜏ex
XN, XS column-averaged
mole fraction (ppb)
𝜏ex interh. exchange (yr)
𝐸N, 𝐸S emission (ppb yr-1)
λ atmos. lifetime (yr)
25 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
FTIR spectrometry – Zugspitze observatory
Ground-based
solar absorption
FTIR spectrometry
at Zugspitze
Spectral resolution:
~ 0.005 cm-1
Mid-infrared region:
2400 - 3100 cm-1
(3 - 4 µm)
26 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
FTIR spectrometry – trace gas retrieval
Forward model
Inverse model
non-linear, ill-posed problem
minimize cost function
𝒙 - trace gas vertical profile
𝒚 - measured spectrum
regularization cost
𝒚 − 𝑭(𝒙) 𝑻 𝑺𝜺−𝟏 𝒚 − 𝑭(𝒙)
+ (𝒙 − 𝒙𝒂)𝑻 𝑹 𝒙 − 𝒙𝒂
spectral error cost
27 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
FTIR spectrometry – retrieval strategy
Methane Ethane
Strategy Sussmann et al., 2011 NDACC IRWG, 2014
Microwindows
(cm-1)
2613.7 – 2615.4
2835.5 – 2835.8
2921.0 – 2921.6
2976.7 – 2977.0
2983.2 – 2983.6
Line list HITRAN 2000
(+ 2001 update)
C2H6 pseudo-lines
(Franco et al., 2015)
Regularization Tikhonov-L1, DOFS ~ 2.1 Tikhonov-L1, DOFS ~ 1.6
Sussmann et al., 2011
28 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Long-term trends – methane and ethane
Trend (ppb yr-1) 1999 – 2006
Zugspitze Lauder
2007 – 2014
Zugspitze Lauder
Methane 0.8 [0.0, 1.6] 1.3 [0.6, 1.9] 6.2 [5.6, 6.9] 6.0 [5.3, 6.7]
Ethane (× 10-2) -0.5 [-1.0, 0.1] -0.4 [-0.7, -0.2] 2.3 [1.8, 2.8] -0.4 [-0.6, -0.1]
Hausmann,
Sussmann,
and Smale;
ACP, 2016
29 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Positive CH4
growth 2007–14
at both sites
Stronger inter-
annual variability
for 1999–2006
Strong biomass
burning events:
2002/03, 2012/13;
2010 in Lauder
Long-term trends – annual growth rates
30 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Two-box model – uncertainties (ethane)
Parameter Range Trend (ppb yr-1) Reference
Lifetime (month) 2.6 [2.0, 3.2] 2.27 [1.79, 2.72] Xiao et al. (2008)
Interh. exchange (yr) 0.98 [0.55, 1.41] 2.27 [2.11, 2.35] Patra et al. (2009)
NH emission fraction (%):
Biomass burning 53 [48, 58] 2.27 [2.26, 2.27] GFED4s
Biofuel use 81 [73, 89] 2.27 [2.26, 2.27] Xiao et al. (2008)
Coal 90 [81, 99] 2.27 [2.26, 2.27] Schwietzke et al. (2014)
Oil and gas 95 [86, 100] 2.27 [2.11, 2.35] Schwietzke et al. (2014)
Overall ethane emission increase
from oil and natural gas production
2007 – 2014
ΔEC2H6, oil & gas, opt. = 1 – 11 Tg yr-1
31 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Two-box model – uncertainties (methane)
Parameter Range Trend (ppb yr-1) Reference
Lifetime (yr) 8.90 [7.90, 9.90] 6.21 [5.88, 6.53] Turner et al., 2015
Interh. exchange (yr) 0.98 [0.55, 1.41] 6.21 [6.10, 6.32] Patra et al., 2009
NH emission fraction (%) 0.70 [0.65, 0.75] 6.21 [6.14, 6.28] Kai et al., 2011
Global emissions (Tg yr-1)
1980s 541 [500, 592] 6.21 [7.51, 4.60] IPCC 2013
1990s 554 [529, 596] 6.21 [7.87, 3.42] IPCC 2013
2000s 553 [526, 569] 6.21 [3.55, 7.79] IPCC 2013
Overall methane emission increase 2007 – 2014
ΔECH4, total, opt. = 24 – 45 Tg yr-1
32 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Two-box model –
Optimized emission scenarios
Overall emission increase 2007 – 2014
ΔEC2H6, oil & gas, opt. = 1 – 11 Tg yr-1
ΔECH4, total, opt. = 24 – 45 Tg yr-1
Contribution of oil & gas emissions
to renewed methane increase
C =
Scenario MER Contribution
Oil & gas 3.3–7.6 39–160 %
Oil (limit) 1.7–3.3 18–72 %
Gas (limit) 7.6–12.1 73–280 %
ΔEC2H6, oil & gas, opt. × MER
ΔECH4, total, opt.
Hausmann et al., 2016
33 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
-20 -10 0 10 20 [cm-1]
I(
)/I 0
Tutorial greenhouse effect: saturation of line absorption
transmitted spectral irradiance I(), unit [W / (m2 cm-1)] ?
Beer-Lambert I() = I0 e - sij f() c l
34 │ Ralf Sussmann: Methane increase after 2006 - reconciling source attributions
Outgoing longwave radiation flux (midlatitude winter
conditions, Modtran simulation)
Tutorial greenhouse effect: greenhouse potential
greenhouse potential of CH4: 84 (20 years), 28 (100 years)