Circumpolar Arctic Tundra Vegetation Change is Linked to Sea-ice Decline

We use a newly available arctic Normalized Difference Vegetation Index dataset (a measure of vegetation photosynthetic capacity) to document coherent temporal relationships between near coastal sea ice, summer tundra land-surface temperatures, and vegetation productivity. We find that during the period of satellite observations (1982–2008), sea ice within 50km of the coast during the period of early-summer ice break up declined an average of 25% for the Arctic as a whole with much larger changes in the E. Siberia Sea to Chukchi Sea sectors (>44% decline). The changes in sea-ice conditions are most directly relevant and have the strongest effect on the villages and ecosystems immediately adjacent to the coast, but the terrestrial effects of sea-ice changes also extend far inland. Low-elevation (<300 m) tundra summer land temperatures, as indicated by the summer warmth index (SWI = sum of the monthly mean temperatures above freezing, expressed as °C mo), have increased an average of 5°C mo (24% increase) for the Arctic as a whole; the largest changes (+10 to 12°C mo) have been in the Chukchi Sea and Bering Sea regions. The land warming has been more pronounced in North America (+30%) than in Eurasia (16%). When expressed as percentage change, areas in the high Arctic in the vicinity of the Greenland Sea, Baffin Bay, and Davis Strait have experienced the largest changes (>70%). The NDVI has increased across most of the Arctic with some exceptions in the Bering and W. Chukchi seas. The greatest change in absolute maximum NDVI occurred in the northern Alaska/Beaufort Sea region (+0.08 AVHRR NDVI units). When expressed as percentage change, large NDVI changes (10-15%) occurred in the North America High Arctic and Beaufort Sea regions. Ground observations along an 1800-km climate transect in North America support the strong correlations between satellite NDVI observations and summer land temperatures. Other new observations from near the Lewis Glacier, Baffin Island, Canada, document rapid vegetation changes along the margins of large retreating glaciers and may be partly responsible for the large NDVI changes observed in northern Canada and Greenland. The ongoing changes to plant productivity will affect many aspects of arctic systems including changes to active-layer depths, permafrost, biodiversity, wildlife and human use of these regions. Ecosystems that are presently adjacent to year-round (perennial) sea-ice are likely to experience the greatest changes.