permafrost feedbacks before and after 2100€¦ · permafrost feedbacks before and after 2100 c. d....
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Permafrost feedbacks before and after 2100
C. D. Koven, D. M. LawrenceJune 20, 2017
IPCC‐AR5 (Ciais et al., 2013)
Most of the carbon in the terrestrial system is frozen in high latitude soils
CLM4.5 includes a representation of permafrost effects on carbon storage, and thus allows exploration of
feedbacks from permafrost
Observations
Precipitation (mm/yr)
Climate models project large losses of permafrost area with warming in the
21st century
Koven et al., (2013)
Slater and Lawrence, (2013)
CLM4.5 shows large losses of carbon; sensitive to assumptions about the cycling of carbon at depth
• 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
Feedback terms: carbon‐concentration(β) and carbon‐climate(γ) from permafrost region
Global CMIP5 values: Arora et al., 2013 Regional CLM4.5 values for permafrost
γPF=.04‐.11 W m‐2 K‐1.08‐.14 W m‐2 K‐1
Threshold,Negative curvature
Long‐term carbon‐climate feedback in CLM4.5
Carbon‐climate feedback from permafrost region
Carbon‐climate feedback from entire terrestrial system
Difference between blue and red curves due to question of how to compute feedback — i.e. magnitude of synergistic effects between CO2 and climate change.
Projected soil C emissions follow the retreating permafrost boundary and persist long after
permafrost has thawed
Koven et al., PNAS, 2015
Carbon losses from permafrost may be large; similar magnitude to, but slower than, carbon responses of tropical forests
Koven et al., PNAS, 2015
Summary
• Permafrost carbon‐climate feedbacks strong contributor to overall terrestrial feedback in CLM4.5
• Delayed feedback relative to tropical/temperate dynamics; threshold at around 4C global temperature change