Frost, G. V., U. S. Bhatt, H. E. Epstein, L. T. Berner, J. W. Bjerke, B. C. Forbes, S. J. Goetz, M. J. Lara, M. J. Macander, G. K. Phoenix, M. K. Raynolds, H. Tømmervik, and D. A. Walker. 2020. Tundra greenness. In J. Richter-Menge and M. L Druckenmiller, eds., State of the climate in 2019. Special on-line supplement to the Bulletin of the American Meteorological Society 101(8):S272–S274. DOI:10.1175/BAMS-D-20-0086.1.
One of the most widespread and conspicuous manifestations of Arctic climatic and environmental change has been an increase in the productivity and biomass of tundra vegetation, a phenomenon commonly termed “the greening of the Arctic.” Trends in the productivity of tundra ecosystems, however, have not been uniform in direction or magnitude across the circumpolar Arctic, and there has been substantial inter-annual variability (Bhatt et al. 2013, 2017; National Academies of Sciences, Engineering and Medicine 2019). This variability arises from a web of interactions that link the vegetation, atmosphere, sea ice, seasonal snow cover, ground (soils, permafrost, and topography), disturbance processes, and herbivores of the Arctic system (Duncan et al. 2019; Piao et al. 2019; Myers-Smith et al. 2020).
Many of the changes observed in tundra ecosystems are producing a cascade of effects on Earth’s subsurface, surface, and atmosphere within and beyond the far north (Post et al. 2019). For example, changes in the composition and height of tundra vegetation impact the cycling of carbon and nutrients (Blume-Werry et al. 2019; Hewitt et al. 2019; Mörsdorf et al. 2019; Salmon et al. 2019; Treharne et al. 2019), as well as energy exchanges between the atmosphere and permafrost (Wilcox et al. 2019). The latter has implications for permafrost stability, geomorphology, and surface wetness, which, coupled with changing vegetation structure, strongly alters landscape properties important to wildlife (Cray and Pollard 2018; Tape et al. 2018; Taylor et al. 2018; Ims et al. 2019; Farquharson et al. 2019; Andruko et al. 2020) and the subsistence activities of Arctic peoples (Brinkman et al. 2016; Veldhuis et al. 2018; Herman-Mercer et al. 2019). Continued monitoring of the Arctic tundra biome both from space and in situ field studies improves our understanding of these complex interactions.