Report Card

Vegetation in the Arctic tundra has been responding dynamically over the course of the last several decades to environmental changes, many of which are anthropogenically-induced. These vegetation changes throughout the circumpolar Arctic are not spatially homogeneous, nor are they temporally consistent (e.g. Bhatt et al. 2013), suggesting that there are complex interactions among atmosphere, ground (soils and permafrost), vegetation, and herbivore components of the Arctic system. Changes in Arctic tundra vegetation may have a relatively small impact on the global carbon budget through photosynthetic uptake of CO₂, compared to changes in other carbon cycling processes (Abbott et al. 2016). However, tundra vegetation can have important effects on permafrost, hydrological dynamics, soil carbon fluxes, and the surface energy balance (e.g. Blok et el. 2010, Myers-Smith and Hik 2013, Parker et al. 2015). Tundra vegetation dynamics also control the diversity of herbivores (birds and mammals) in the Arctic, with species richness being positively related to vegetation productivity (Barrio et al. 2016). To improve our understanding of these complex interactions and their impacts on the Arctic and global systems, we continue to evaluate the state of the circumpolar Arctic vegetation.

Arctic air temperatures are both an indicator and a driver of regional and global changes. Although there are year-to-year and regional differences in air temperatures due to natural random variability, the magnitude and Arctic-wide character of the long-term temperature increase is a major indicator of global warming (Overland 2009). Here we report on the spatial and temporal variability of Arctic air temperatures during the period October 2014 through September 2015, the 12-month period since the end of the previous reporting period (Overland et al. 2014).

The Arctic (land areas north of 60°N) is always completely snow covered in winter, so it is the transition seasons of fall and spring that are significant when characterizing variability and change…

Estimates of the spatial extent of melting across the Greenland ice sheet in 2015, derived from spaceborne brightness temperatures recorded by the Special Sensor Microwave Imager/Sounder (SSMIS) passive microwave radiometer (e.g., Mote 2007; Tedesco 2007; Tedesco et al. 2013), show that melting occurred over more than half of the ice sheet for the first time since the exceptional melt events of July 2012…