Transcript Permafrost in CCSM3

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
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
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
Soil Temperature Trends
Romanovsky et al. 2002
Recent Permafrost Temperature Trends
(adapted from Romanovsky et al. 2002)
Country
Region
Permafrost
Temp. Trend
Reference
USA
Trans-Alaska pipeline route (20 m),
1983-2003
+0.6 to +1.5°C
Romanovsky and Osterkamp,
2001; Osterkamp 2003
USA
Barrow Permafrost Observatory (15 m),
1950-2003
+1°C
Brewer 1958; Romanovsky et
al., 2002
Russia
Northwest Siberia (10 m), 1980-1990
+0.3 to +0.7°C
Pavlov, 1994
Russia
European North of Russia (6 m), 19731992
+1.6 to +2.8°C
Pavlov, 1994
Canada
Alert (15 m), 1995-2000
+0.15°C yr-1
Smith et al., 2003
Canada
Northern Quebec (10 m), late 1980s mid 1990s
–0.1oC yr-1
Allard et al., 1995
Norway
Janssonhaugen, Svalbard
+1° to +2°C
Isaksen et al., 2001
Kazakhstan
Northern Tien Shan (1973-2003)
+0.2° to +0.6°C
Marchenko, 1999 and 2002
Tibet
Qinghai-Tibet Plateau (1970s-90s)
+0.1 to +0.3°C
Huijin et al., 2000
Mongolia
Khentei and Khangai Mountains, Lake
Hovsgol (1973-2003)
+0.3° to +0.6°C
Sharkhuu, 2003
Arctic Land Area: Surface Air Temperature Change
(CCSM3)
Near-Surface Permafrost in CCSM3
CCSM3
(1980 – 1999)
IPA Permafrost
Distribution Map
Continuous
Discontinuous
Sporadic
Isolated
CCSM3 Projections of Degradation of
Near-Surface Permafrost
Are the CCSM3 Projections Plausible?
Model Validation: Annual Mean Surface Air
Temperature and Active Layer Thickness
CALM Monitoring Sites
CCSM3
Observed
CCSM3 – Obs
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
Kudryavtsev, 1974
25m Soil Column
0.05m layers
15 year run
Kudryavtsev, 1974
3.43m Soil Column
CLM3 resolution
15 year run
25m Soil Column
0.05m layers
15 year run
3.43m Soil Column
CLM3 resolution
15 year run
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
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
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
Appearing and Disappearing Lakes in Siberia (Smith et al. 2005)
Smith et al., 2005
Release of Soil Carbon Frozen in Permafrost
• ~ 200 – 800 Pg C frozen in
permafrost soil
• Increased wetlands,
anaerobic microbial activity 
CH4 emissions
• Dry, well-drained soil, aerobic
decomposition  CO2
emissions
Photo courtesy Natural Resources Canada
• At one Swedish mire,
permafrost and vegetation
changes linked with 22-66% rise
in CH4 emissions
(1970 to
2000, Christensen et al. 2004).
Release of Soil Carbon Frozen in Permafrost
Global Carbon Project
?
Permafrost
Permafrost
Permafrost
Gruber et al. 2004
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
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
Arctic Land Area: Surface Air Temperature Change
(CCSM3)