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.
Highlights
Background and RationaleThe remotely sensed Normalized Difference Vegetation Index (NDVI) documents that arctic tundra vegetation greenness has overall increased [1,2,3,4,5,6,7,8] during the satellite record and is linked to increased vegetation productivity as measured by above-ground biomass [9,10,11,12]
The Arctic Ocean was divided into sub-regions (Figure 1) modified from the Arctic Atlas of Treshnikov [44], and the adjacent land divisions approximately follow the floristic provinces of the Circumpolar Arctic Vegetation Map [21]
The unique features of this study include the examination of tundra vegetation changes in the context of various measures of climate variability, such as sea ice and large-scale circulation
Summary
The remotely sensed Normalized Difference Vegetation Index (NDVI) documents that arctic tundra vegetation greenness has overall increased [1,2,3,4,5,6,7,8] during the satellite record and is linked to increased vegetation productivity as measured by above-ground biomass [9,10,11,12] This pan-Arctic tundra vegetation greening is associated with increases in summer warmth [2,10] that are, in large-part, driven by summer sea-ice retreat along arctic coasts based on observational [13,14,15,16] and modeling studies [17,18,19]. These factors are very important for understanding the very heterogeneous signals that are coming from global assessments of plot-scale response to experimental warming [23]
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