Greening of the Arctic: A "Plant to Planet" Analysis of Vegetation Change in the Arctic

Models show that reduced sea-ice will likely affect land surface temperatures and permafrost, but it is not clear how these changes will affect the vegetation. The Greening of the Arctic (GOA) IPY project examined the circumpolar patterns of tundra vegetation photosynthetic capacity as measured by the Normalized Difference Vegetation Index (NDVI) in relationship to variations in coastal sea-ice concentrations, land temperatures and various types of disturbance. We used a newly-derived NDVI data set (GIMMS 3g) and ground information at several sites. From 1982 to 2008, the Northern Hemisphere MaxNDVI increased 5% but was regionally variable ranging from -5% in the E. Bering Sea to +15% in Baffin Bay. The strongest NDVI changes were in the Beaufort Sea area and in the High Arctic of Canada and Greenland. The NDVI was strongly correlated to summer ground temperatures and more weakly, but still significantly, correlated to changes in early summer coastal sea-ice concentrations. A wide variety of ground observations across the full Arctic climate gradient provided further documentation of the nature of the greening trends. A "Back to the Future" project obtained repeat photos separated by 46 years that illustrate the effect of rapidly retreating glaciers on Baffin Island in the High Arctic. A long-term study by the Earth Cryosphere Institute examined shrubification on landslides triggered by extreme ice-rich permafrost conditions of the Yamal Peninsula. A study at Toolik Lake, Alaska, used repeat Landsat images to determine where the greening is occurring most rapidly within landscapes. A study in the forest-tundra transition of Ural Mountains used 1968 Corona satellite and 2003 Quickbird images to examine shrubification resulting from wildfire. An International Tundra Experiment (ITEX) study at Toolik Lake studied changes to vegetation structure and composition. A "Environmental and Social Impacts of Industrialization in Northern Russia" (ENSINOR) project linked the willow growth rings to climate and NDVI records. While the NDVI trend is widespread and linked to sea-ice and summer soil temperature changes, the actual ground-level evidence of the greening is difficult to document. The most rapid changes are generally occurring where there are fine-grained soils, strong natural and anthropogenic disturbance regimes, and relatively high supply of water and nutrients. As the summer sea ice vanishes the fastest percentage changes are occurring in the High Arctic.