G. V. Frost1, M. J. Macander1, U. S. Bhatt2, L. T. Berner3,4, J. J. Assmann5, A. Bartsch6, J. W. Bjerke7,8, H. E. Epstein9, B. C. Forbes10, M. J. Lara11,12, E. López-Blanco13, R. Í. Magnússon14, P. M. Montesano15,16, C. S. R. Neigh15, K. M. Orndahl4, G. K. Phoenix17, G. Schaepman-Strub5, H. Tømmervik7, C. Waigl18, D. A. Walker19, D. Yang20, and Q. Zhou15,21
1Alaska Biological Research, Inc., Fairbanks, AK, USA
2Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA
3Department of Natural Sciences, University of Alaska Southeast, Juneau, AK, USA
4School of Informatics, Computing and Cyber Systems, Northern Arizona University, Flagstaff, AZ, USA
5Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
6b.geos GmbH, Korneuburg, Austria
7Norwegian Institute for Nature Research, FRAM – High North Research Centre for Climate and the Environment, Tromsø, Norway
8Tromsø Arctic-Alpine Botanical Garden, The Arctic University Museum of Norway, UiT The Arctic University of Norway, Tromsø, Norway
9Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA
10Arctic Centre, University of Lapland, Rovaniemi, Finland
11Department of Plant Biology, University of Illinois, Urbana, IL, USA
12Department of Geography, University of Illinois, Urbana, IL, USA
13Department of Ecoscience and Arctic Research Centre, Aarhus University, Roskilde, Denmark
14Plant Ecology and Nature Conservation Group, Wageningen University & Research, Wageningen, Netherlands
15Goddard Space Flight Center, NASA, Greenbelt, MD, USA
16ADNET Systems, Inc., Bethesda, MD, USA
17School of Biosciences, University of Sheffield, Sheffield, UK
18International Arctic Research Center, University of Alaska Fairbanks, Fairbanks AK, USA
19Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
20Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
21Science Systems and Applications, Inc., Lanham, MD, USA
Headlines
- In 2025, the circumpolar mean maximum tundra greenness value was the third highest in the high-resolution 26-year MODIS satellite record, continuing a sequence of record or near-record high values since 2020.
- First detected in the late 1990s, the “greening of the Arctic” is a long-term increase in the productivity and abundance of tundra vegetation that remains evident in all available long-term satellite records.
- Tundra greenness is increasing across most of the Arctic due to rapid warming, but there are many localized areas of decline that reflect disturbances such as wildfire and extreme weather events.
- Tundra greening has far-reaching impacts to Arctic landscapes, wildlife habitats, biodiversity, permafrost conditions, and the livelihood of Arctic people, with implications for global climate and the carbon cycle.
Introduction
Earth’s northernmost continental landmasses and island archipelagos are home to the Arctic tundra biome, which collectively encompasses a 5.1 million km2 region bounded by the Arctic Ocean to the north and the boreal forest biome to the south (Raynolds et al. 2019). While Arctic tundra ecosystems are treeless and lack the vertical structure of forests, they present rich variation across spatial scales, reflecting both broad latitudinal climate gradients as well as landscape-scale differences in soil, hydrology, permafrost conditions, wildlife habitat use, and more (Fig. 1). For thousands of years, Arctic ecosystems have accumulated large amounts of carbon, as cold temperatures greatly slow decomposition and a large proportion of vegetation biomass becomes preserved in permafrost. In recent decades, the Arctic has warmed dramatically (see essay Surface Air Temperature), far exceeding the global rate of warming and placing the circumpolar region at the forefront of global climate and environmental change. Today, the circumpolar region lies at the crossroads of multiple feedback mechanisms that connect the living Arctic with a warming climate, declining nearshore sea ice, changing seasonal snow cover, thawing permafrost soils that contain large amounts of carbon, and industrial development (Bartsch et al. 2025; Vonk et al. 2025). Some of the most compelling evidence of broad-scale changes in this remote region comes from long-term satellite observations that began in 1982. By the late 1990s, Earth-observing satellites began to detect a sharp increase in the productivity of tundra vegetation, a phenomenon known today as “the greening of the Arctic.”
Spaceborne monitoring of tundra greenness
The earliest consistent spaceborne record of Arctic vegetation began in 1982 with the launch of the Advanced Very High Resolution Radiometer (AVHRR) sensor; however, funding for the AVHRR-derived Global Inventory Modeling and Mapping Studies 3g V1.2 dataset (GIMMS-3g+), which long underpinned reports of Arctic greening, ceased in 2025 after 43 years of record (see essay Assessing the State of the Arctic Observing Network). At present, the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Landsat series of satellites provide the longest active spaceborne records of tundra greenness. MODIS is nearing the end of its service life, but continuity of this important record will be maintained by its successor, the Visible Infrared Imaging Radiometer Suite (VIIRS). All of these instruments monitor vegetation greenness using the Normalized Difference Vegetation Index (NDVI), a spectral metric of plant biomass that exploits the unique way in which green vegetation absorbs and reflects visible and near-infrared light. We summarize greenness observations for each growing season by calculating the Maximum NDVI (MaxNDVI), representing vegetation biomass at the height of the Arctic summer, typically during July and August.
All three long-term records show increasing annual maximum tundra greenness (MaxNDVI) across most of the circumpolar Arctic during 1982-2024 (GIMMS-3g+) and 2000-25 (MODIS and Landsat), respectively (Fig. 2). MODIS (Fig. 3a), GIMMS-3g+ (Fig. 3b), and Landsat (not shown) all display widespread greening trends in continental Eurasia and North America, except for portions of southwestern Alaska, and central and northeastern Siberia where flat or negative (“browning”) trends are evident. Trends in the Canadian Arctic Archipelago are somewhat mixed, which may be partly due to different observational periods among sensors, as well as observational challenges posed by the very short growing season, persistent cloudiness, and high interannual variability in snowmelt and surface water in High Arctic environments (Zemlianskii et al. 2025). Regional contrasts in greening highlight the complexity of Arctic change and the rich web of interactions that exist between tundra ecosystems and the local properties of sea ice (see essay Sea Ice), permafrost, seasonal snow (see essay Terrestrial Snow Cover), soil composition and moisture, microtopography, disturbance processes, wildlife, and human activities (Frost et al. 2025). Understanding the underlying drivers of complex Arctic trends is important for improved monitoring and prediction of tundra ecosystem functions and the consequences of Arctic change on the global carbon cycle.
The neighboring boreal forest biome (see Fig. 3) occupies large swaths of northern Eurasia and North America and has also emerged as a focal point of global environmental change. Patches of positive and negative greenness trends are widely interspersed, reflecting the biome’s active disturbance regime and differential responses of boreal forests as a function of latitude. Browning has generally prevailed in the warmer southern boreal zone, where warming temperatures have promoted drought-stress and increased wildfire; however, greening has been widespread in colder parts of the biome along the northern forest-tundra ecotone (Berner and Goetz 2022).
In 2025, the MODIS-observed circumpolar average MaxNDVI value was nearly identical (-0.2%) compared to 2024 and represents the third highest value in the 26-year record for that sensor. This continued a sequence of record or near-record high values that began in 2020, with the five highest MaxNDVI values in the 26-year MODIS record being observed since that year. Tundra greenness was much higher than normal across most of the North American Arctic, particularly in northern Alaska, Quebec, and Labrador (Fig. 4). The Eurasian Arctic, however, featured a mixture of positive and negative departures from normal, a pattern that has recurred for the last several years. Nonetheless, the long-term trend in MODIS-observed tundra greenness is strongly positive (greening) for most of the circumpolar region. The last circumpolar average MaxNDVI value from GIMMS-3g+ in 2024 was the fifth highest in the 43 years of record for that sensor; although no longer maintained, this dataset provides the most unequivocal signal of long-term Arctic greening, with four of the five highest MaxNDVI values in the 43-year record all observed since 2020 (Fig. 2).
Drivers and consequences of Arctic greening
Earth-observing satellites provide foundational datasets for monitoring Arctic environmental change and help to overcome the long-standing access barriers posed by the region’s remoteness, as well as new ones arising from the cessation of international cooperation in the Russian Arctic and cutbacks in funding and logistical support for Arctic research and spaceborne monitoring capabilities in the United States and the European Union. Nonetheless, field studies provide crucial information needed to connect spaceborne observations with patterns and drivers of change (or stability) on the ground. Increases in the abundance, distribution, and height of Arctic shrubs are a major component of Arctic greening (Frost et al. 2025). The development of taller plant canopies is particularly impactful in tundra ecosystems, with important consequences for biodiversity, seasonal snow cover, permafrost temperatures, biogeochemical cycling, forage availability for animals, and human land uses (García Críado et al. 2025; Shuman et al. 2025; Rearden and Fienup-Riordan 2014). However, while changes to the Arctic climate have generally favored greening, ecological disturbances, extreme events, and other causes of browning (a decline in productivity that is opposite to greening) are also increasing in frequency (Phoenix et al. 2025). For example, greening trends in many parts of the Arctic have been partially offset by increasing wildfires during the past two decades, and permafrost thaw can produce strong local “hotspots” of browning associated with thermokarst and changes in surface water extent (Assmann et al. 2025). Understanding the regional variability of complex Arctic greening trends and attributing its drivers continues to be a subject of multidisciplinary scientific research (Fig. 1).
Methods and data
The satellite record of Arctic tundra greenness began in 1982 using AVHRR, a sensor that collects daily observations; while this sensor continues to operate, the AVHRR-derived Global Inventory Modeling and Mapping Studies 3g V1.2 dataset (GIMMS-3g+) (Pinzon et al. 2023) that long underpinned Arctic greenness monitoring is no longer funded after 43 years of record (1982-2024). Therefore, we also report observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Landsat series of satellites, which are higher spatial resolution systems that provide circumpolar greenness observations since 2000. The latter two records generally display less interannual variability in MaxNDVI than the legacy GIMMS-3g+ dataset, likely reflecting their higher spatial resolution and improved calibration (Frost et al. 2025). For MODIS, we computed tundra greenness trends for 2000-25 with a higher spatial resolution of 500 m, combining 16-day Vegetation Index products from Terra (MOD13A1, version 6.1) and Aqua (MYD13A1, version 6.1) (Didan 2021a,b), referred to here as MCD13A1. Landsat provides tundra greenness data at a much higher spatial resolution of 30 m; we computed time-series of greenness from Landsat Collection 2 (Crawford et al. 2023) using the methods of Berner and Goetz (2022). Circumpolar maps depicting greenness trends (AVHRR and MODIS only) cover the Arctic tundra biome, as well as boreal forest and non-Arctic tundra above 60° N latitude. For time-series plots, data were masked to include only ice-free land within the extent of the Circumpolar Arctic Vegetation Map (Raynolds et al. 2019). MODIS and Landsat data were further masked to exclude permanent water based on the 2015 MODIS Terra Land Water Mask (MOD44W, version 6). We summarize the GIMMS-3g+, MODIS, and Landsat records for Maximum NDVI (MaxNDVI), the peak yearly value that is typically observed during the months of July and August.
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November 13, 2025