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Koven c 20150707_1700_upmc_jussieu_-_room_101

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Koven c 20150707_1700_upmc_jussieu_-_room_101

  1. 1. Projecting the carbon-climate feedback from thawing permafrost Charlie Koven, Lawrence Berkeley National Lab P. Ciais, P. Friedlingstein, G. Grosse, J. W. Harden, G. Hugelius, D. M. Lawrence, A. D. McGuire, W. J. Riley, C. Schädel, E. A. G. Schuur Support from DOE-BER: BGC-Uncertainties SFA, NGEE Arctic, IMPACTS projects
  2. 2. IPCC-AR5 (Ciais et al., 2013) Permafrost contains enormous amount of carbon, twice what is in the atmosphere
  3. 3. ESM predictions of carbon-climate feedback (which don’t include permafrost) Predict carbon gains with warming (negative feedback) in arctic Current models of global carbon cycle feedbacks do not include permafrost carbon pool and its role as a feedback agent IPCC-AR5 (Ciais et al., 2013) Simplified estimates of permafrost suggest it is most important term not yet included in models
  4. 4. Harden, Koven, et al., GRL, 2012 Photo: Soil Atlas of the Northern Circumpolar Region Much of the C in permafrost is well below the surface, stabilized there by processes such as cryoturbation
  5. 5. Climate models project large losses of permafrost area with warming in the 21st century. More losses with more warming. Koven et al., (2013) Slater and Lawrence, (2013)
  6. 6. Laboratory incubations of permafrost soils suggest a substantial fraction will be respired to atmosphere after thaw 10 years C:N 0 20 40 60 80 1 year 0 20 40 60 80 Closs(%ofinitialC) 0 20 40 60 80 100 50 years 0 20 40 60 80 Fast C pool 0 20 40 60 80 Cpoolsize(%oftotalC) 0 2 4 6 8 10 12 14 Slow C pool C:N 0 20 40 60 80 0 20 40 60 80 100 Passive C pool 0 20 40 60 80 0 20 40 60 80 100 Incubation length (days) 0 500 1000 1500 2000 4500 Numberofstudies 0 2 4 6 8 10 12 14 16 18 Schädel et al., 2014 • Carbon losses of 10-40% on many decades timescale can be expected from thawed soils
  7. 7. Models that do include permafrost carbon processes project potentially strong emissions from region with warming 0 100 200 300 400 500 Raupach and Canadell (2008) Harden et al. (2012) MacDougall et al. (2012) Schuur et al. (2013) Burke et al. (2012) Schaefer et al. (2011) Gruber et al. (2004) Schuur et al. (2009) Schneider et al. (2012) Koven et al. (2011) Burke et al. (2013) Dutta et al. (2006) Zuang et at. (2006) Cumulative Emissions (Gt C) Series1 Series2 Series3 2100 2200 2300 Schuur et al., 2015
  8. 8. Combining physical thaw models with soil carbon maps and incubation data suggests a linear relation between carbon loss and global warming Koven et al., accepted • Large difference in magnitude of carbon losses between medium emissions (RCP4.5) and high emissions (RCP8.5) scenarios
  9. 9. Ecosystem models suggest total magnitude of carbon loss is a sensitive function of deep soil decomposability • With decomposable deep soil organic matter, soil C losses dominate and lead to a large positive feedback from the permafrost region • Inclusion of nitrogen cycle suggests that plants may not effectively use extra nitrogen released by decomposing deep soils to mitigate C losses Koven et al., PNAS, 2015
  10. 10. Projected soil C emissions follow the retreating permafrost boundary and persist long after permafrost has thawed Koven et al., PNAS, 2015
  11. 11. Carbon losses from permafrost may be large; similar magnitude to, but slower than, carbon responses of tropical forests Koven et al., PNAS, 2015
  12. 12. Conclusions • Permafrost may be large positive carbon-climate feedback. • No evidence for large-scale thresholds in total permafrost C losses, but relatively linear with warming. – Large differences in outcomes between medium- emissions (RCP4.5) and high-emissions (RCP8.5) scenarios • Nitrogen feedbacks unlikely to offset permafrost carbon losses. • Once thawed, emissions persist for a long time.

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