David Lawrence 1 and Andrew Slater 2

1. A Projection of Severe Degradation of Near-Surface Permafrost: Potential Feedbacks on Global Climate David Lawrence1 and Andrew Slater2 1 NCAR / CGD Boulder, CO 2 NSIDC / CIRES Boulder, CO

2. Permafrost: Soil or rock that remains below freezing for two or more years IPA Permafrost Distribution Map Continuous Discontinuous Continuous (90 – 100% coverage) Discontinuous (50 – 90%) Sporadic (10 – 50%) Isolated (0 – 10%) Brown et al. 1998

3. Observed Arctic Climate Change • Polar amplification of climate change • Arctic air temperatures rising at twice the rate of rest of world • Arctic sea-ice extent decreasing • Arctic glaciers retreating • Shrub coverage expanding • Treeline migrating northward • Arctic tundra may have shifted from a CO2 sink to a CO2 source • Permafrost temperatures rising ACIA, 2004; Serreze et al. 2000

4. Soil Temperature Trends Romanovsky et al. 2002

5. Recent Permafrost Temperature Trends (adapted from Romanovsky et al. 2002)

6. Arctic Land Area: Surface Air Temperature Change (CCSM3)

7. Near-Surface Permafrost in CCSM3 IPA Permafrost Distribution Map CCSM3 (1980 – 1999) Continuous Discontinuous Sporadic Isolated

8. CCSM3 Projections of Degradation of Near-Surface Permafrost

9. Are the CCSM3 Projections Plausible?

10. Model Validation: Annual Mean Surface Air Temperature and Active Layer Thickness CALM Monitoring Sites CCSM3 Observed CCSM3 – Obs

11. Model Validation and Development Priorities: Permafrost Simulation • Soil temperature data • Russian hydromet / agromet sites (long time series) Problems: No associated meteorological data Comparison of site data with gridded model data • Soil depth • Increase from 3.5m to 15m • Organic soil layer / mosses • Alter thermal conductivity and heat capacity for uppermost soil levels • Discontinuous permafrost • High-res land model, topographic, aspect • Solve Arctic low cloud bias Photo by A. Slater

12. Kudryavtsev, 1974 25m Soil Column 0.05m layers 15 year run

13. Kudryavtsev, 1974 3.43m Soil Column CLM3 resolution 15 year run

14. 25m Soil Column 0.05m layers 15 year run 3.43m Soil Column CLM3 resolution 15 year run

15. Model Validation and Development Priorities: Permafrost Simulation • Soil temperature data • Russian hydromet / agromet sites (long time series) Problems: No associated meteorological data Comparison of site data with gridded model data • Soil depth • Increase from 3.5m to 15m • Organic soil layer / mosses • Alter thermal conductivity and heat capacity for uppermost soil levels • Discontinuous permafrost • High-res land model, topographic, aspect • Solve Arctic low cloud bias Photo by A. Slater

16. Are the CCSM3 Projections Plausible? Uncertainties in timing and amplitude of projected permafrost degradation – - biases in simulated climate - imperfect representation of permafrost - feedbacks that are not fully-represented What are the impacts / climate feedbacks? - vegetation - expansion of shrub coverage and northward forest migration - hydrologic cycle - freshwater discharge to Arctic Ocean, lake and wetland expansion/contraction - carbon cycle – release of frozen soil carbon

17. Impact on Freshwater Discharge to Arctic Ocean Runoff to Arctic Ocean • 28% increase in freshwater discharge to Arctic Ocean (2000 to 2099) • ~15% due to soil ice melting and drainage of excess soil water • Impacts on Arctic sea-ice formation and ocean circulation Runoff P – E

18. Appearing and Disappearing Lakes in Siberia (Smith et al. 2005) Smith et al., 2005

19. Release of Soil Carbon Frozen in Permafrost Photo courtesy Natural Resources Canada • ~ 200 – 800 Pg C frozen in permafrost soil • Increased wetlands, anaerobic microbial activity  CH4 emissions • Dry, well-drained soil, aerobic decomposition  CO2 emissions • At one Swedish mire, permafrost and vegetation changes linked with 22-66% rise in CH4 emissions (1970 to 2000, Christensen et al. 2004).

20. Release of Soil Carbon Frozen in Permafrost Global Carbon Project ? Permafrost Permafrost Permafrost Gruber et al. 2004

21. Climate Feedbacks Associated with Permafrost Degradation: Model Development Issues • Northward expansion of shrubs and forests • Introduce shrubs into DGVM • Update parameters for Arctic vegetation types • Hydrology, freshwater discharge to Arctic Ocean • ‘Dynamic’ wetland and lake distributions • Frozen soil hydrology • Emission of soil carbon from thawing permafrost soil • Spin-up (or initialization) of soil carbon store in permafrost (vertical profile of soil carbon, low GPP in Arctic?) • Partition soil decomposition emissions into CH4 or CO2 depending on moisture conditions

22. Summary • Permafrost temperatures are rising and permafrost is degrading in some locations • CCSM3, which reasonably simulates present-day near-surface permafrost conditions, projects severe degradation of near-surface permafrost during the 21st century • The potential feedbacks associated with a loss of near-surface permafrost are diverse (vegetation, hydrologic cycle, carbon cycle) and could contribute to an acceleration of climate change

23. Arctic Land Area: Surface Air Temperature Change (CCSM3)