1 Climate feedback from wetland methane emissions GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L20503, doi: /2004GL020919, 2004 N. Gedney Hadley Centre, Met Office, Joint Centre for Hydro-Meteorological Research, Wallingford, UK P. M. Cox Hadley Centre, Met Office, Exeter, UK C. Huntingford Centre for Ecology and Hydrology, Wallingford, UK

2 Outline Introduction into the global methane cycle Model examples Presentation of the paper itself

3 Methane sources/sinks Total source approx. 600 Tg/year Source: NASA/GISS Main sink: OH radical (90%) Further: Oxidation in soil, transport to stratosphere

4 What triggers methane formation Biological methane formation (70-80% of total source) is an anaerobic process, microbial digestion of organic matter (by methanogens)

5 What triggers methane formation Most CH 4 released by methanogens is oxidised by methanotrophs (less in wet conditions) There is still a temperature dependence since microbial activity strongly depends on T: higher T  higher CH 4 flux

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7 Methane cycle On a global scale in principle simple since the sinks are simple (90% oxidation by OH radicals) Total burden of the atmosphere: 4850 Tg ppb), lifetime approx. 8.6 years but dependent on [CH 4 ] itself)

8 Methane steady state, whole earth [CH 4 ] = 4850 Tg/Earth (1750 ppb), tau=8.6 years  Flux = 560 Tg/year

9 Two hemispheres Tau hemisphere is approx 1 year The question is how much each hemisphere contributes to the total flux of methane and how this influences the N-S gradient

10 Assuming 75% on northern hemisphere and 600 Tg/year total flux

11 N-S difference [%] with respect to source strength

12 Finally, the paper Idea: Methane flux is triggered by temperature and should thus exhibit a positive feedback on climate change Goal: 1) parameter identification of this T-dependence from past climatological measurements 2) extrapolation into the future until 2100

13 Methods Temperature sensitivity Q 10 : factor by which flux increases at a 10° temperature increase (Literature: ) Global constant Wetland fractionSoil carbon

14 Model run Met office climate model coupled to land-surface scheme MOSES-LSH Methane emission scheme: Invert Q 10 and total wetland flux from the methane time series of Dlugokencky (variability of human sources can be neglected, some major biomass burnig events taken into account)

15 Model-Measurement RMS

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17 21 st century projection Incorporation of the wetland model into the „Integrated Model of Global Effects on climatic aNomalies“ (IMOGEN) GCM model which allows climate feedback IPCC Scenario IS92a

18 Results Control run (CTL) total T increase 4.2°

19 Conclusion Approximate doubling of wetland CH 4 emission by 2004 (comparable to the IS92a projected increase) Radiative forcing accounts only for K ( % of total increase)  small effect despite doubling of CH 4 Feedback of northern peatlands could be stronger but better knowledge of carbon cycling including CO 2 AND CH 4 is necessary

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