Vegetation productivity trends for the Arctic tundra are updated for the 1982–2011 period and examined in the context of land surface temperatures and coastal sea ice. Understanding mechanistic links between vegetation and climate parameters contributes to model advancements that are necessary for improving climate projections. This study employs remote sensing data: Global Inventory Modeling and Mapping Studies (GIMMS) Maximum Normalized Difference Vegetation Index (MaxNDVI), Special Sensor Microwave Imager (SSM/I) sea-ice concentrations, and Advanced Very High Resolution Radiometer (AVHRR) radiometric surface temperatures. Spring sea ice is declining everywhere except in the Bering Sea, while summer open water area is increasing throughout the Arctic. Summer Warmth Index (SWI—sum of degree months above freezing) trends from 1982 to 2011 are positive around Beringia but are negative over Eurasia from the Barents to the Laptev Seas and in parts of northern Canada. Eastern North America continues to show increased summer warmth and a corresponding steady increase in MaxNDVI. Positive MaxNDVI trends from 1982 to 2011 are generally weaker compared to trends from 1982–2008. So to better understand the changing trends, break points in the time series were quantified using the Breakfit algorithm. The most notable break points identify declines in SWI since 2003 in Eurasia and 1998 in Western North America. The Time Integrated NDVI (TI-NDVI, sum of the biweekly growing season values of MaxNDVI) has declined since 2005 in Eurasia, consistent with SWI declines. Summer (June–August) sea level pressure (slp) averages from 1999–2011 were compared to those from 1982–1998 to reveal higher slp over Greenland and the western Arctic and generally lower pressure over the continental Arctic in the recent period. This suggests that the large-scale circulation is likely a key contributor to the cooler temperatures over Eurasia through increased summer cloud cover and warming in Eastern North America from more cloud-free skies.

It is often assumed that the Normalized Difference Vegetation Index (NDVI) can be equated to aboveground plant biomass, but such a relationship has never been quantified at a global biome scale. We sampled aboveground plant biomass (phytomass) at representative zonal sites along two trans-Arctic transects, one in North America and one in Eurasia, and compared these data to satellite-derived NDVI. The results showed a remarkably strong correlation between total aboveground phytomass sampled at the peak of summer and the maximum annual NDVI (R ² = 0.94, p < 0.001). The relationship was almost identical for the North America and Eurasia transects. The NDVI–phytomass relationship was used to make an aboveground phytomass map of the tundra biome. The approach uses a new and more accurate NDVI data set for the Arctic (GIMMS3g) and a sampling protocol that employs consistent methods for site selection, clip harvest and sorting and weighing of plant material. Extrapolation of the results to zonal landscape-level phytomass estimates provides valuable data for monitoring and modelling tundra vegetation.

Summer warming is driving a greening trend across the Arctic, with the potential for large-scale amplification of climate change due to vegetation-related feedbacks [Pearson et al., Nat. Clim. Chang. (3), 673–677 (2013)]. Because observational records are sparse and temporally limited, past episodes of Arctic warming can help elucidate the magnitude of vegetation response to temperature change. The Last Interglacial ([LIG], 129,000 to 116,000 y ago) was the most recent episode of Arctic warming on par with predicted 21st century temperature change [Otto-Bliesner et al., Philos. Trans. A Math. Phys. Eng. Sci. (371), 20130097 (2013) and Post et al., Sci. Adv. (5), eaaw9883 (2019)]. However, high-latitude terrestrial records from this period are rare, so LIG vegetation distributions are incompletely known. Pollen-based vegetation reconstructions can be biased by long-distance pollen transport, further obscuring the paleoenvironmental record. Here, we present a LIG vegetation record based on ancient DNA in lake sediment and compare it with fossil pollen. Comprehensive plant community reconstructions through the last and current interglacial (the Holocene) on Baffin Island, Arctic Canada, reveal coherent climate-driven community shifts across both interglacials. Peak LIG warmth featured a ∼400-km northward range shift of dwarf birch, a key woody shrub that is again expanding northward. Greening of the High Arctic—documented here by multiple proxies—likely represented a strong positive feedback on high-latitude LIG warming. Authenticated ancient DNA from this lake sediment also extends the useful preservation window for the technique and highlights the utility of combining traditional and molecular approaches for gleaning paleoenvironmental insights to better anticipate a warmer future. Significance The Arctic is warming exceptionally rapidly, promoting an expansion of shrubs across the Arctic with global-scale climate implications. The Last Interglacial (∼125,000 y ago) was the most recent time the Arctic was warmer than present and thus serves as an analogue for Arctic greening in the near future. Ancient plant DNA in lake sediment from this time reveals major ecosystem changes in response to warmth, including an ∼400 km northward shift of dwarf birch relative to today. Enhanced shrub cover, corroborated by molecular and microfossil analyses, amplified warming during the Last Interglacial and will likely play a similar role in the future. This record constitutes the oldest authenticated plant DNA from lake sediment yet reported, increasing the technique’s temporal potential.