Satellite data indicates recent Arctic peatland expansion with warming.

Northern peatlands are an important carbon store in mid to high latitudes, but become increasingly discontinuous in the higher latitudes, associated with temperature and precipitation limits on plant growth. During the last four decades, mean annual temperatures in the Arctic have increased on average by ~3 °C. Warmer temperatures and longer growing seasons likely drive increases in plant productivity throughout northern latitudes, but it is not clear whether warming has resulted in lateral spread of Arctic peatlands. Using long time-series Landsat satellite data, coupled with information gathered from fieldwork in situ, we show that Arctic peatlands have likely undergone lateral expansion over the last 40 years. On 21 transects from the edges of 16 extant peatlands in the European and Canadian Arctic (both high and low Arctic locations from 62 to 79°N), over two thirds of the peatland edges we studied showed statistically significant peak-summer greening (as Normalised Difference Vegetation Index) in the last 15 to 20 years, compared to the period 1985-1995. Peak summer moisture (as normalised Difference Moisture Index) levels remained stable or increased at most study sites. The lateral expansion of Arctic peatlands suggests they are an increasingly important natural carbon sink, at least in the near term.