renewed increase in atmospheric methane: review on … · 2019. 7. 8. · 14 │ ralf sussmann:...

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


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


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


Inman, Nature, 2014

Why quantify oil & gas contribution to

atmospheric methane increase?

• oil & gas production increased after 2006:


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.)


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


Ethane-based CH4-source

attribution: oil & gas contrib.


Contribution

Oil & Gas 3.3–7.6 39–160 %


NH SH


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?


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.


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!


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


• 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


• 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


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


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 ‰


Renewed methane increase –

Optimized emission scenarios


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 %


NH SH


ΔECH4

C =


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


Leakage threshold value of 3.2 % for immediate

climate benefit

based on Alvarez et al. (2012)


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?


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 %


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


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)


Two-box model – setup (2)


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)


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)


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


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


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


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


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


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


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


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


Outgoing longwave radiation flux (midlatitude winter

conditions, Modtran simulation)

Tutorial greenhouse effect: greenhouse potential

greenhouse potential of CH4: 84 (20 years), 28 (100 years)

renewed increase in atmospheric methane: review on … · 2019. 7. 8. · 14 │ ralf sussmann:...

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