The Changing Terrestrial Arctic
Terry Chapin
Polar regions are the cooling system for Planet Earth
Mann et al.
Chapman and Walsh
Global to arctic
Polaramplification
Polar warming is driven by global processes
• Is mitigation of impacts the only option?
• Can SEARCH make the case that– Warming has significant ecological impacts?– Warming is affecting human well-being?
• Within the Arctic?• Beyond the Arctic?
-500
-400
-300
-200
-100
0
100
200
300
1960 1970 1980 1990 2000 2010
BaaBeaBraBarctic
Glacie volume change, km^3
YearChange in volume of Arctic ice caps and mountain glaciers
Aerial extent of glaciers is decreasing(decreasing albedo)
(positive feedback to warming)
European arctic
Russian arctic
Total arctic
American arctic
Hinzman
Spring snowmelt is earlier
• Decreased albedo
• Positive feedback to warming
Sea ice is less extensive
• Decreased albedo
• Positive feedback to warming
• Together these changes in physical environment contribute to polar amplification of global warming
Lloyd and Fastie
Forests are expanding
Forests are expanding
• Decreased albedo– Less masking of snow– Darker, more complex canopy
• Positive feedback to warming
1949
Chandler River, 50 miles S. of Umiat: Sturm, Racine and Tape: Fifty Years of Change in Arctic Alaskan Shrub Abundance
Shrub density has increased
1949
2000
Sturm
Indigenous observations indicate that shrub expansion
is widespread
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Jia et al. GRL, in press
Simulated increase in July temperature
due to shrub expansion
Chapin , Lynch et al.
15 20 25 30Sqrt ADDT (air, º C day)
35
40
45
50
55
60
Grid
Average Thaw Depth (cm)
97
98
99
00
9596
97
98
99
00
97
98
99
00
97
98
99
00
97
99
00
97
98
99
00
97
98
99
00
Stefan Best Fit (R2)Atqasuk (0.84)
Barrow (0.81)
BettyPingo (0.33)
WestDock (0.17)
HappyValley (0.79)
Toolik (0.75)
Imnavait (0.83)
Hinkel, Brown and Nelson
Relationship of air temperature to thaw depthdepends on surface properties
1983 1986 1989 1992 1995 1998 2001
-10.0
-9.5
-9.0
-8.5
-8.0
-7.5
-7.0
-6.5
-6.0
Temperatures at the 20 m depth on a N-S transect across the coastal plain of Northern Alaska
Franklin Bluffs
Deadhorse
West Dock
Tom Osterkamp 10/01
Temperature (°C)
Year
Permafrost temperatures are warming warmer air altered thermal insulation
Osterkamp and Romanovsky
Permafrost is thawingin many places,
not just southern margins
Hinzman
Hydrology is changing(confirmed by indigenous observations)
Oechel and Vourlitis
Tundra is becoming drier(in places)
Oechel et al. Nature August, 2000
Recent Response ofRecent Response ofNet Ecosystem CarbonNet Ecosystem Carbon
Flux to a Secular Change inFlux to a Secular Change inClimateClimate
Oechel et al.
Carbon sequestration is changing(complexity reflects feedbacks)
McGuire
CO2 efflux is sensitive to warming
• Increased sequestration in wet areas
• Increased carbon loss in dry areas
• Net effect uncertain– Probably positive feedback to warming
Methane efflux is increasing
• Positive feedback to warming– Sensitive to hydrology
• Overall trace-gas effect is a positive feedback to warming
Area burned in W. North America has doubled in last
20 years
Kasischki
Fire effects on climate
• Releases carbon to atmosphere – (positive feedback)
• Reduces masking of snow – (increased winter albedo, negative feedback)
• Increases vegetation albedo – (negative summer feedback)
Warming effects on human well-being
Economic impacts are a mixed bag
Warming effects on arctic well-being (cultural effects generally negative)
Warming effects on global well-being Economic effects generally negative Magnitude still uncertain
(Arcticnations)
Global-to-arctic: important, understoodArctic-to-global: poorly understood