Importance of methane and nitrous oxide for Europe’s terrestrial greenhouse-gas balance

Climate change negotiations aim to reduce net greenhouse-gas emissions by encouraging direct reductions of emissions and crediting countries for their terrestrial greenhouse-gas sinks. Ecosystem carbon dioxide uptake has offset nearly 10% of Europe’s fossil fuel emissions, but not all of this may be creditable under the rules of the Kyoto Protocol. Although this treaty recognizes the importance of methane and nitrous oxide emissions, scientific research has largely focused on carbon dioxide. Here we review recent estimates of European carbon dioxide, methane and nitrous oxide fluxes between 2000 and 2005, using both top-down estimates based on atmospheric observations and bottom-up estimates derived from ground-based measurements. Both methods yield similar fluxes of greenhouse gases, suggesting that methane emissions from feedstock and nitrous oxide emissions from arable agriculture are fully compensated for by the carbon dioxide sink provided by forests and grasslands.
As a result, the balance for all greenhouse gases across Europe’s terrestrial biosphere is near neutral, despite carbon sequestration in forests and grasslands. The trend towards more intensive agriculture and logging is likely to make Europe’s land surface a significant source of greenhouse gases. The development of land management policies which aim to reduce greenhouse-gas emissions should be a priority.

1. Meinhausen, M. et al. Greenhouse-gas emissions targets for limiting global warming to 2 °C. Nature 458, 1158–1162 (2009).
2. http://unfccc.int/Kyoto_protocol/items/2830.php.
3. Schulze, E.‑D. & Heimann, H. Carbon and water exchange of terrestrial systems in Asian Change in the Context of Global Change Vol. 3
(eds Galloway, J. N. & Melillo, J.)145–161 (Cambridge Univ. Press, 1998).
4. Schulze, E. D. & Caldwell, M. M. Ecophysiology of Photosynthesis
(Springer, 1994).
5. Epstein, E. & Bloom, A. J. Mineral Nutrition of Plants: Principles and Perspectives (Sinauer, 2005).
6. Jung, M., Herold, M., Henkel, K. & Churkina, G. Exploring synergies of land cover products for carbon cycle modeling. Remote Sens. Environ.
101, 534–553 (2006).
7. Gifford, R. M. A comparison of potential photosynthesis, productivity and yield of plant species with differing photosynthetic metabolism.
Aust. J. Plant Physiol. 1, 107–117 (1994).
8. Schulze, E.‑D. in Encyclopedia of Plant Physiology. Physiological Plant
Ecology II. Vol. 12B. Water Relations and Photosynthetic Productivity
(eds Lange, O. L., Nobel, P. S., Osmond, C. B. & Ziegler, H.) 615–676
(Berlin, 1982).
9. Rillig M. C. Arbuscular mycorrhizae and terrestrial ecosystem processes.
Ecol. Lett. 7, 740–754 (2004).
10. Ciais, P. et al. Carbon accumulation in European forests. Nature Geosci.
1, 1–5 (2008).
11. German Advisory Council on Global Change Welt im Wandel — Zukunftsfähige Bioenergie und Nachhaltige Landnutzung (WBGU, 2008).
12. Sims, R. E. H., Hastings, H., Schlamadinger, B., Taylor, G. & Smith, P.
Energy crops: Current status and future perspectives. Glob. Change Biol.
12, 2054–2076 (2006).
13. IPCC Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) (Cambridge Univ. Press, 2008).
14. Jungkunst, H. F. & Fiedler, S. Latitudinal differentiated water table
control of carbon dioxide, methane and nitrous oxide fluxes from hydromorphic soils: Feedbacks to climate change. Glob. Change Biol.
13, 2668–2683 (2007).
15. Peylin, P. et al. Daily CO2 flux estimates over Europe from continuous atmospheric measurements: 1, inverse methodology. Atmos. Chem. Phys.
5, 3173–3186 (2005).
16. Roedenbeck, C., Houweling, S., Gloor, M. & Heimann, M. CO2 flux
history 1982–2001 inferred from atmospheric data using a global
inversion of atmospheric transport. Atmos. Chem. Phys.
3, 1919–1964 (2003).
17. Peters, W. et al. Seven years of recent European net terrestrial carbon dioxide exchange constrained by atmospheric observations. Glob. Change Biol.
(in the press)
18. Bousquet, P. et al. Contribution of anthropogentic and natural
sources to atmospheric methane variability. Nature
443, 439–443 (2006).
19. Manning, A. J., Ryall, D. B., Derwent, R. G., Simmonds, P. G. & O’Doherty, S. Estimating European emissions of ozone-depleting and greenhouse gases using observations and a modeling back-attribution technique. J. Geophys. Res.
108, D14,4405 (2003).
20. Huang, J. et al. Estimation of regional emissions of nitrous oxide from 1997 to 2005 using multinetwork measurements, a chemical transport model, and an inverse model. J.Res. 113, D17313 (2008).
21. Hirsch, A. I. et al. Inverse modeling estimates of the global nitrous
oxide surface flux from 1998–2001. Glob. Biogeochem. Cycles
20, GB1008 (2006).
22. Messager, C. Ten years of CO2, CH4, CO and N2O fluxes over Western Europe inferred from atmospheric measurements at Mace Head, Ireland.
Atmos. Chem. Phys. Discuss. 8, 1191–1237 (2008).
23. Luyssaert, S. et al. The European carbon balance revisited. Part 3: Forests.
Glob. Change Biol. (in the press).
24. Soussana, J. F. et al. Full accounting of the greenhouse gas (CO2, N2O, CH4) budget of nine European grassland sites. Agr. Ecosyst. Environ.
121, 121–134 (2007).
25. Ciais, P. et al. The European carbon balance revisited. Part 2: Croplands.
Glob. Change Biol. (in the press).
26. Drösler, M., Freibauer, A., Christensen, T. R. & Friborg, T. Observations and status of peatland greenhouse gas emissions in Europe. Ecol. Studies
203, 237–256 (2008).
27. Saarnio, S., Winiwarter, W. & Leitão, J. Methane release from wetlands
and watercourses in Europe. Atmos. Environ. 43, 1421–1429 (2009).
28. Janssens, I. A. et al. Europe’s terrestrial biosphere absorbs 7 to 12 %
of the European anthropogenic CO2 emissions. Science
300, 1538–1542 (2003).
29. Pacala, S. W. et al., Consistent land- and atmosphere-based US carbon sink estimates. Science 292, 2316–2320 (2001).
30. Luyssaert, S. et al. CO2-balance of boreal, temperate and tropical
forests derived from a global database. Glob. Change Biol.
13, 1–29 (2007).
31. Shvidenko, A. & Nilsson, S. Dynamics of Russian forests and the carbon
budget in 1961–1998: an assessment based on long-term inventory data. Climatic Change 55, 5–37 (2002).
32. Shvidenko, A., Nilsson, S., Stolbovoi, V. S., Rozhkov, V. A. & Gluck, M. Aggregated estimation of basic parameters of biological production and the carbon budget of Russian terrestrial ecosystems 2: Net primary production. Russ. J. Ecol. 32, 71–77 (2001)
33. German Advisory Council on Global Change World in Transition: Towards Sustainable Energy Systems (Earthscan, 2004).
34. Magnani, F. et al. The human footprint in the carbon cycle of temperate an boreal forests. Nature 447, 849–851 (2007).
35. Smith, P. et al. Greenhouse gas mitigation in agriculture. Phil. Trans. R. Soc. B 363, 789–813 (2008).
36. Janssens, I. A. & Luyssaert, S. Nitrogen’s carbon bonus. Nature Geosci.
2, 318–319 (2009).
37. Jackson, R. B. et al. Protecting climate with forests. Environ. Res. Lett.
3, 044006 (2008).
38. Ciais P. et al. The European carbon balance revisited. Part 4: Fossil fuel emissions. Glob. Change Biol. (in the press).
39. Etiope, G., Friddriksson, T., Italiano, F., Winiwarter, W. & Theloke, J. Natural emissions of methane from geothermal and volcanic sources in Europe. J. Volcanol. Geoth. Res. 165, 76–86 (2007).
40. Etiope, G. Natural emissions of methane from geological seepage in Europe. Atmos. Environ. 43, 1430–1443 (2009).
41. Ciais, P. et al. The impact of lateral carbon fluxes on the European carbon balance. Biogeosciences 5, 1259–1271 (2008).
42. Profft, I., Mund, M., Weber, G. E., Weller, E. & Schulze, E. D. Forest management and carbon sequestration in wood products. Eur. J. For. Res.
(in the press).
43. http://unfccc.int/resources/docs/2008/sbi/eng/12.pdf.
44. Meybeck, M. Global Distribution and Behaviour of Carbon Species in World
Rivers in Soil Erosion and Carbon Dynamics (eds Rose, E., Lal, R.,
Feller, C., Barthès, B. & Steward, B. A.) 209–238 (Chemical Rubber Co.
Press, 2005).
45. Smith, K. A. et al. Oxidation of atmospheric methane in Northern European soils, comparison with other ecosystems, and uncertainties in the global terrestrial sink. Glob. Change Biol. 6, 791–803 (2000)