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Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra
Geophysical Institute, Department of Atmospheric Sciences, College of Natural Science and Mathematics, University of Alaska Fairbanks, 903 Koyukuk Dr., Fairbanks, AK 99775, USA
Institute of Arctic Biology, Department of Biology and Wildlife, College of Natural Science and Mathematics, University of Alaska, Fairbanks, P.O. Box 757000, Fairbanks, AK 99775, USA
International Arctic Research Center, Department of Atmospheric Sciences, College of Natural Science and Mathematics, 930 Koyukuk Dr., Fairbanks, AK 99775, USA
Department of Environmental Sciences, University of Virginia, 291 McCormick Rd., Charlottesville, VA 22904, USA
Cryospheric Sciences Branch, NASA Goddard Space Flight Center, Code 614.1, Greenbelt, MD 20771, USA
Biospheric Science Branch, NASA Goddard Space Flight Center, Code 614.1, Greenbelt, MD 20771, USA
* Author to whom correspondence should be addressed.
Received: 15 June 2013; in revised form: 17 July 2013 / Accepted: 19 August 2013 / Published: 29 August 2013
Abstract: Vegetation productivity trends for the Arctic tundra are updated for the 1982–2011 period and examined in the context of land surface temperatures and coastal sea ice. Understanding mechanistic links between vegetation and climate parameters contributes to model advancements that are necessary for improving climate projections. This study employs remote sensing data: Global Inventory Modeling and Mapping Studies (GIMMS) Maximum Normalized Difference Vegetation Index (MaxNDVI), Special Sensor Microwave Imager (SSM/I) sea-ice concentrations, and Advanced Very High Resolution Radiometer (AVHRR) radiometric surface temperatures. Spring sea ice is declining everywhere except in the Bering Sea, while summer open water area is increasing throughout the Arctic. Summer Warmth Index (SWI—sum of degree months above freezing) trends from 1982 to 2011 are positive around Beringia but are negative over Eurasia from the Barents to the Laptev Seas and in parts of northern Canada. Eastern North America continues to show increased summer warmth and a corresponding steady increase in MaxNDVI. Positive MaxNDVI trends from 1982 to 2011 are generally weaker compared to trends from 1982–2008. So to better understand the changing trends, break points in the time series were quantified using the Breakfit algorithm. The most notable break points identify declines in SWI since 2003 in Eurasia and 1998 in Western North America. The Time Integrated NDVI (TI-NDVI, sum of the biweekly growing season values of MaxNDVI) has declined since 2005 in Eurasia, consistent with SWI declines. Summer (June–August) sea level pressure (slp) averages from 1999–2011 were compared to those from 1982–1998 to reveal higher slp over Greenland and the western Arctic and generally lower pressure over the continental Arctic in the recent period. This suggests that the large-scale circulation is likely a key contributor to the cooler temperatures over Eurasia through increased summer cloud cover and warming in Eastern North America from more cloud-free skies.
Keywords: AVHRR NDVI3g; tundra vegetation; climate variability; sea ice; Arctic
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Bhatt, U.S.; Walker, D.A.; Raynolds, M.K.; Bieniek, P.A.; Epstein, H.E.; Comiso, J.C.; Pinzon, J.E.; Tucker, C.J.; Polyakov, I.V. Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra. Remote Sens. 2013, 5, 4229-4254.
Bhatt US, Walker DA, Raynolds MK, Bieniek PA, Epstein HE, Comiso JC, Pinzon JE, Tucker CJ, Polyakov IV. Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra. Remote Sensing. 2013; 5(9):4229-4254.
Bhatt, Uma S.; Walker, Donald A.; Raynolds, Martha K.; Bieniek, Peter A.; Epstein, Howard E.; Comiso, Josefino C.; Pinzon, Jorge E.; Tucker, Compton J.; Polyakov, Igor V. 2013. "Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra." Remote Sens. 5, no. 9: 4229-4254.