Understanding Methane Concentrations Nicola Warwick 1, Euan Nisbet 2, John Pyle 1 1- Centre for...
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Transcript of Understanding Methane Concentrations Nicola Warwick 1, Euan Nisbet 2, John Pyle 1 1- Centre for...
Understanding Methane Concentrations
Nicola Warwick1,
Euan Nisbet2, John Pyle1
1- Centre for Atmospheric ScienceUniversity of Cambridge
2 – Royal Holloway, University of London
Quest CH4 Workshop, June 2004
Outline
• CH4 observations
• Understanding the global distribution and seasonal cycles
• Understanding variability and trends
• Outlook
Factors controlling CH4
• Emissions (natural and anthropogenic)• Sinks (OH, soil)• Meteorology (winds, temperatures, rainfall)
July model surface CH4 (ppbv)
July Surface OH in model (106molecules/cm3)
Methane Measurements
• In-situ and flask data:Global network of 40-50 stations mainly including: US-NOAA-CMDLAustralian CSIRONew Zealand NIWAMeth-MonitEUr – European Network
• Satellite observations
• Ice-cores
Observed CH4 1992-2002
• Observed CH4 mixing ratios (Marine Boundary Layer) from 1992 to 2001, NOAA-CMDL
Southern Hemisphere
Northern Hemisphere
CH4 Measuring Stations
Mace Head
AlertNy-Ålesund
Mace HeadParisHeidelberg /SchauinslandKrakow / KasprowySt. PetersburgOb RiverLondon
Main methane sourceregions
PallasWetlandand gasAtlantic background airreaches west Europeanmargins
Meth-MonitEUr: Methane monitoring in the European region.
How Mean Carbon-Gas Concentrations have varied with Time
0
200
400
600
800
1000
1200
Dec-95 Dec-96 Dec-97 Dec-98 Dec-99 Dec-00 Dec-01 Dec-02 Dec-03
CO/ppb - 90 CH4/ppb - 1800 (CO2/ppm - 360) x 10
Ny-Alesund
Ny-Alesund
Mace Head
AlertNy-Ålesund
Mace HeadParisHeidelberg /SchauinslandKrakow / KasprowySt. PetersburgOb RiverLondon
Main methane sourceregions
PallasWetlandand gasAtlantic background airreaches west Europeanmargins
Meth-MonitEUr: Methane monitoring in the European region.
How Mean Carbon-Gas Concentrations have varied with Time
0
200
400
600
800
1000
1200
Dec-95 Dec-96 Dec-97 Dec-98 Dec-99 Dec-00 Dec-01 Dec-02 Dec-03
CO/ppb - 90 CH4/ppb - 1800 (CO2/ppm - 360) x 10
Royal Holloway College, W London (provided by E. Nisbet, D. Lowry)
Testing our understanding of CH4
• Global modelling (forward and inverse)
• Regional modelling
• Back trajectory analyses / diurnal experiments
• Isotopes
December surface CH4 by MATCH model (provided by Kim Holmen, NILU)
13C-CH4 Isotopic Fractionation of CH4
Sources
Light Heavy
Methane sources have a wide range of distinct 13CH4 signatures further constraint on emission scenarios.
Adapted from Chanton et al. [2000]
-47%
KIE
Global CH4 and 13CH4 Distributions
Wetlands
Fossil Fuel
Rice Surface 13CH4 (‰) - January monthly
mean
Surface CH4 (ppbv) - January monthly mean
How well do measurements describe the CH4 burden?
Blue line: modelled zonal mean CH4 and 13C-CH4
Red Circles: modelled CH4 and 13C-C-CH4 at measuring station locations
Black squares: observed CH4 and 13C-CH4 [Dlugokencky et al., 1998, Miller et al., 2002]
Houwelling et al. (1999): relative contribution of NH sources decrease from 77% to 67%.
Breakdown of seasonal cycles by source
Southern Hemisphere
(Modelled CH4 at Ascension Island,
Atlantic, 7°S)
Northern Hemisphere
(Modelled CH4 at Alert, Canada, 82°N)
Alternative Emission Scenarios
Source / Tg Scenario 1 (base)
Scenario 2 (wtnd)
Scenario 3 (ff)
Scenario 4
(wtld&ff)
Wetlands 115 61 115 85
Fossil Fuel 89 89 35 65
Biomass Burning
54 108 108 108
Other 254 254 254 254
Global Total (Tg/yr)
512 512 512 512
Alternative Emission Scenarios: Results
Niwot Ridge, Colorado
(106W, 40N)
Cape Grim, Tasmania
(145E, 41S)
South Pole
(25W, 90S)
Measurements courtesy of NOAA/CMDL/CCGG
Understanding Interannual Variability and Trends
Feedback Timescales
Year-to-Year Millennial and Longer…
Petit, J.R., et al., 2001, Vostok Ice Core Data for 420,000 Years, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2001-076. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA.
Dlugokencky et al., 1998, 2003
NOAA Observed Interpolar Gradient
Dlugokencky et al., GRL, 2003
CH4 Variability due to Meteorology
• Black line = observed growth rate
• Dashed line = modelled growth rate
Correlation Coefficients:
Key Biscayne, r=0.61 Ascension, r=0.59
Modelled and Observed CH4 Variations
Simulated CH4 interannual variability arising from changes
in the circulation
Observed CH4 growth rate (NOAA CMDL Carbon Cycle
Greenhouse Gases)
• Changes in modelled interpolar gradient resulting from meteorology: ~up to 0.5%
Influence of Meteorology on CH4
• Tropics: – OH (will vary with humidity) – Tropical forest fires / wetlands– El Niño
Influence of el Nino on fire emissions – van der Werf et al., 2004.
Measured CH4 at Ascension Island (D. Lowry, E. Nisbet)
Influence of Meteorology on CH4
• Tropics: – OH (will vary with humidity) – Tropical forest fires / wetlands– El Nino– Winds (alter inter-hemispheric mixing)
• Northern Latitudes:– Northern wetlands
1700
1800
1900
2000
2100
2200
2300
2400
2000 2001 2002 2003Year
ÑÍ4 concentration, ppb
Yamal
Teriberka
St. Cape Kamenny St. New Port
CH4 measurements at Yamal Peninsula compared to Teriberka background level
Problems and Outlook
• Model simulations still have trouble reproducing CH4 observations– Need more continental data (e.g. South America, Africa
Asia) to test models
• Satellites: – look for abrupt changes (e.g tropical fires)– infer surface fluxes (need high precision)
• Isotopes:– High-precision ground-based isotope measurements can
distinguish sources (help quantify wetland source)
The End
The global CH4 burden may be higher than previously thought.....
• Use modelled radon concentrations to distinguish between ‘clean’ and ‘dirty’ air
• True global mean = 1.3% greater than ‘clean’ global mean• By 2008-12, Kyoto Protocol envisages reduction in GHG emissions of
~5% w.r.t. 1990 values
Modelled annual mean surface CH4 / ppbv
Observed and modelled CH4 seasonal cycles
The Atmospheric CH4 Record: 1000 to 2000
Change in CH4 abundance for the last 1000 years.
IPCC TAR Fig 4-1.
Carbon Gas Measurements: 1996-2003
Carbon gas measurements at Royal Holloway College, W London (provided by E. Nisbet, D. Lowry)
How Mean Carbon-Gas Concentrations have varied with Time
0
200
400
600
800
1000
1200
Dec-95 Dec-96 Dec-97 Dec-98 Dec-99 Dec-00 Dec-01 Dec-02 Dec-03
CO/ppb - 90 CH4/ppb - 1800 (CO2/ppm - 360) x 10
CH4 Variability due to Sinks
• Prinn et al. 2001: 1.4 ± 2.1% yr-1 upward trend 1979-1989
2.3% yr-1 downward trend 1990-2000
• Krol et al. 1998, 2001: 1978-1993, 0.46 ± 0.6% yr-1
• Krol and Lelieveld 2003: possible problems with CH3CCl3 data.
• Dentener et al. 2003: 1979-1993, 0.24 ± 0.06% yr-1
large interannual variability of OH (1.5%)