The Changing Effects of Arctic Terrestrial. University of Alaska Fairbanks

Transcription

1 The Changing Effects of Arctic Terrestrial Ecosystems on the Climate System Eugénie Euskirchen Eugénie Euskirchen University of Alaska Fairbanks

2 The Terrestrial Arctic Grey Area = Tundra Green Area = Permafrost Sum of Grey plus Green = The Arctic

3 Climate influences the terrestrial ecosystems The terrestrial ecosystems influence the climate Increase in surface reflectivity Decreased CO 2

4 ADJACENT OCEAN EXCHANGE DIC: ~1.1 Pg C yr -1 CO 2 : Tg DOC: Tg C yr -1 C yr -1 sink CH 4 : Gg CH 4 yr -1 SEA ICE ARCTIC OCEAN STOCKS DIC: 310 Pg C DOC: 9 Pg C SEDIMENT: 9 Pg C CH 4 : 0-3 Tg CH 4 Flux to Sediment: ~2 Tg C yr -1 ARCTIC OCEAN FLOOR CH 4 HYDRATE: Pg CH 4 ATMOSPHERIC PERSPECTIVE CO 2 : 0.4 ± 0.4 Pg C yr -1 surface sink CH 4 : Tg CH 4 yr -1 surface source CH 4 : 1-12 Tg CH 4 yr -1 source River POC: ~6 Tg C yr -1 River PIC: 0 4 Tg C yr -1 Erosion POC: ~8 Tg C yr -1 Flux to Sediment: ~9 Tg C yr -1 DIC: ~43 Tg C yr -1 DOC: ~33 Tg C yr -1 CH 4: 1-11 Gg CH 4 yr -1 ARCTIC CONTINENTAL SLOPE PERMAFROST CH 4 HYDRATE: 2-65 Pg CH 4 CO 2 : Tg C yr -1 source CO 2 : Pg C yr -1 sink CH 4 : Tg CH 4 yr -1 source ARCTIC LAND STOCKS VEGETATION: Pg C SOIL: Pg C SUBTERRANEAN INTRA- and SUB-PERMAFROST CH 4 HYDRATE: Pg CH 4 Literature estimates of Arctic System C pools and fluxes for the late 20 th Century (McGuire et al., Ecological Monographs, in press).

5 Global Distribution of Soil Organic Carbon

6 Spatial Distribution of Near-Surface Permafrost (a) (b) overlaid on (a) (b) (d) (c) (d) Overlaid on (a) (e) Euskirchen et al., 2006

7 Between , the number of days of snow covered ground decreased by an estimated 2.5 days per decade across the pan-arctic. Change in the duration of snow covered 2000 ground (anomaly): < > Days per year shorter Days per year longer Euskirchen et al., 2007

8 Changes in atmospheric heating due to changes in the snow season, Across the pan-arctic, an overall reduction in the duration of snow covered ground by ~2.5 days per decade d resulted in atmospheric heating of ~1.0 W m -2 per decade Heating W m -2 decade -1 Cooling Euskirchen et al., 2007

9 Pan-Arctic Detection of Recent Land Surface Changes Change in Spring Thaw Change Change in Vegetation Gross Primary Productivity Greenness McDonald et al., 2004 Myneni et al., 2001 Days earlier yr-1 <5 Days later yr -1 >55 25 Increase in NDVI (%) Bunn & Goetz, 2006

10 Spruce, willow., other deciduous shrubs, evergreen shrubs not including spruce, sedges, forbs, lichens, and feathermoss Spruce forest Willow-birch tundra Tussock tundra Willow, dwarf birch, other deciduous shrubs evergreen shrubs, sedges, forbs, lichens, & feathermoss Dwarf birch, other deciduous shrubs, evergreen shrubs, sedges, forbs, lichens, feathermoss and Sphagnum moss

11 Change in plant growth across vegetation types, arranged in descending order. The increase in dwarf birch was at least 3 times greater than any other plant. Increased shrubiness Sturm et al., 2001; 2005 Changes in productivity of Arctic vegetation Euskirchen et al., 2009

12 Increases in plant productivity resulted in increases in biomass, and consequently, decreases in summer albedo. This suggests an increase in surface heating (e.g., less heat reflected back to the atmosphere). Sum mmer Albedo Regional Forest Sedge tundra Shrub tundra The albedo of the shrub tundra is approaching that of the forest at the end of the simulation Euskirchen et al., 2009

13 eating de -1 ) ge in he 2 decad Chang (W m -2 6 Increases in atmospheric heating were mostly due to changes in snowmelt in the spring, particularly in the sedge tundra. Change in heating due to change in: 5 Snow melt Snow return 4 Biomass 3 Total Sedge tundra Shrub tundra Forest Regional Euskirchen et al., 2009 Mean

14 Alaska Now FIRE Alaska to Come? MODIS Active Fire Detections, Aug. 5, 2009 Fairbanks Photoshopping courtesy of Mark Chapin

15 Burned ar rea (millio on ha) Historical Burned Area in Alaska Total Burned Area = 10.7 Mha Total Burned area = Burned area per yr = 0.31 Mha/yr 11.5 Mha FRI = 157 years Burned area per yr = 0.52 Mha/yr FRI = 90 years 35 yrs 22 yrs s 1960s 1970s 1980s 1990s 2000s Kasischke et al., in review FRI = Fire return interval

16 The 2007 tundra fire in northern Alaska burned for approximately 3 months, and was the largest tundra fire ever recorded in Alaska.

17 -For how long does higher albedo persist following fire? -This is one of the few estimated negative feedbacks to climate warming in boreal forest ecosystems. High albedo Low albedo

18 Changes in the Age Structure of Forest Ecosystems in Alaska due to a Changing Fire Regime 7x10 4 (a) 0 10 years (b) years (c) years post-fire post-fire post-fire 5 x x x ) Area (km 7x x x10 4 (d) years (e) years (f) years post-fire post-fire post-fire 1 x x x x (g) > 60 years post-fire Year A2 Had. CM3 A2 PCM B2 Had. CM3 B2 PCM Mean Euskirchen et al., in press

19 ating heric Hea ade -1 ) Atmosph m -2 deca ange in A (W Ch Change in Atmospheric Heating ( ) Due To Change in: Summer Albedo (α) Empirical α Modis α Winter Albedo Constant Including Fire Stand Age (no fire) Disturbance Snow melt Snow Total Snow Snow Total return melt return Euskirchen et al., in press

20 Overall Conclusions I Arctic terrestrial ecosystem responses under a warming climate: - Decreases in permafrost extent - Decreases in the length of the snow season - Increases in the growing season length - Changes in plant productivity - Changes in the fire regime, resulting in more young forest stands

21 Overall Conclusions II Climate feedbacks: -Changes in snow cover duration represent a strong positive feedback to climate warming. -A A positive feedback is also found between the increase of shrub abundance and climate warming. -Decreases in permafrost extent represent a possible strong positive feedback to climate warming (only partially counterbalanced by increased plant productivity). -An increase in the number of young stands under an altered fire regime acts as a negative feedback to climate warming.