The Changing Face of the Arctic: Four Decades of Greening and Implications for Tundra Ecosystems

Gerald Verner Frost ^1* Uma Bhatt ² Matthew Macander ¹ Logan T Berner ³ Annett Bartsch ⁴ Jarle Werner Bjerke ^5,6 Howard Epstein ⁷ Bruce C Forbes ⁸ Scott Goetz ³ Elizabeth E Hoy ^10,9 Stein Rune Karlsen ¹¹ Timo Kumpula ¹² Trevor Lantz ¹³ Mark Jason Lara ¹⁴ Efrén López Blanco ¹⁵ Rúna Magnússon ¹⁶ Paul Montesano ⁹ Christopher S Neigh ⁹ Ingmar Nitze ¹⁷ Kathleen M Orndahl ³ Taejin Park ¹⁸ Gareth Phoenix ¹⁹ Martha K Raynolds ²⁰ Adrian Rocha ²¹ Brendan Morris Rogers ²² Gabriela Schaepman-Strub ²³ Hans Tømmervik ²⁴ Mariana Verdonen ^12,25 Alexandra Veremeeva ¹⁷ Anna-Maria Virkkala ²² Christine Waigl ²⁶ Donald A Walker ²⁰ Dedi Yang ²⁷

• ¹ Other
• ² Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, United States
• ³ Northern Arizona University, Flagstaff, Arizona, United States
• ⁴ b.geos GmbH, Korneuburg, Austria
• ⁵ Norwegian Institute for Nature Research, FRAM – High North Research Centre for Climate and the Environment, Tromsø, Norway
• ⁶ UiT The Arctic University of Norway, Tromsø, Troms, Norway
• ⁷ University of Virginia, Charlottesville, Virginia, United States
• ⁸ Arctic Centre, University of Lapland, Rovaniemi, Lapland, Finland
• ⁹ Goddard Space Flight Center, National Aeronautics and Space Administration, Greenbelt, Maryland, United States
• ¹⁰ Global Science and Technology, Inc., Greenbelt, Maryland, United States
• ¹¹ NORCE Norwegian Research Centre AS, Tromsø, Norway
• ¹² University of Eastern Finland, Joensuu, Finland
• ¹³ University of Victoria, Victoria, British Columbia, Canada
• ¹⁴ University of Illinois at Urbana-Champaign, Champaign, Illinois, United States
• ¹⁵ Aarhus University, Aarhus, Central Denmark Region, Denmark
• ¹⁶ Wageningen University and Research, Wageningen, Netherlands
• ¹⁷ Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany
• ¹⁸ Ames Research Center, National Aeronautics and Space Administration, Moffet Field, California, United States
• ¹⁹ The University of Sheffield, Sheffield, England, United Kingdom
• ²⁰ Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, United States
• ²¹ University of Notre Dame, Notre Dame, Indiana, United States
• ²² Woodwell Climate Research Center, Falmouth, Massachusetts, United States
• ²³ University of Zurich, Zürich, Zürich, Switzerland
• ²⁴ Department of Arctic Ecology, Norwegian Institute for Nature Research (NINA), Tromsø, Troms, Norway
• ²⁵ Agricultural University of Iceland, Reykjavik, Iceland
• ²⁶ International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, United States
• ²⁷ Oak Ridge National Laboratory (DOE), Oak Ridge, Tennessee, United States

Arctic landscapes occupy a nexus of environmental change processes, globally significant soil carbon stores, wildlife populations, and subsistence-based human societies. In response to rapid climate warming, tundra ecosystems are experiencing widespread changes to vegetation and underlying permafrost, coupled with an array of ecological disturbances that are expected to intensify in the future. Declines in the extent of the cryosphere on land (permafrost and seasonal snow) and offshore (sea-ice) raise the question of whether and for how long warmer portions of the Low Arctic will fit established concepts of ‘‘what is Arctic,” given the influence the cryosphere has historically had on tundra ecosystem structure and function. The era of spaceborne observation of circumpolar tundra greenness, in the form of the Normalized Difference Vegetation Index (NDVI), has entered its fifth decade and provides foundational information concerning ecosystem conditions and responses to climatic trends, variability, ecological disturbance, and successional processes. Here we review the evolving story of Arctic greening, and synthesize long-term spaceborne records of NDVI, climatic data, field observations, and the knowledge base of Arctic residents to place the last four decades of Arctic environmental change in context, and establish expectations and research priorities for the coming decade. Greenness dynamics display high spatio-temporal variability, reflecting complex interactions of climatic warming and variability, landscape history, ecological disturbance, and other factors. Nonetheless, long-term increases in NDVI—commonly known as “the greening of the Arctic”—remain prominent across large areas in all available long-term spaceborne datasets and align with long-term shifts in vegetation structure documented in disparate Arctic regions. Common shifts reported from the Low Arctic, such as shrubification, generally portend declines in floristic diversity, and shifts in fauna that favor boreal forest species. Despite lingering uncertainties regarding trend attribution and sources of interannual variability, the sequence of record-high circumpolar tundra greenness values observed since 2020 provides strong evidence that Arctic tundra ecosystems have entered a state without historic precedent since at least the Little Ice Age.