Siberia’s Arctic landscape is getting greener

Every spring the Arctic bursts into bloom, turning a blinding white landscape green and brown. In recent years some parts of the Arctic have been getting greener, with Northern Alaska showing a 20% increase in summer greenness since 1982. Some blame climate change for the flourishing vegetation, while others believe that disturbances to the land, such as gas-field development and reindeer grazing, could be a partial cause. A new study shows that the answer isn’t simple.

Scientists measure the greenness of a landscape using light-reflection data gathered by weather satellites. Green plants tend to reflect the near infra-red wavelengths, but absorb red wavelengths for photosynthesis. Using near-infrared and red-wavelength data scientists calculate a "normalized difference vegetation index" (NDVI), where higher numbers represent greener landscapes. This measure provides a good reference for year-to-year change of the amount of tundra productivity over the past 25 years.

To better understand the trends in tundra productivity and how this might be related to the dramatic changes in sea ice that are occurring in the Arctic Ocean, Skip Walker from the University of Alaska and his colleagues have studied 25 years' worth of sea-ice data, summer land temperatures and NDVI values from the Yamal Peninsula, in north-west Siberia.

The Yamal region is an ideal place to understand NDVI because it is relatively flat and simple geologically, the vegetation structure is straightforward and it is a hotspot for Arctic land-cover change. What's more, there is a strong north-south climate gradient along which it is possible to study the effects of climate on greenness patterns.

By studying the satellite data the team found that there had been a 7% increase in NDVI over the Yamal Peninsula between 1982 and 2007. Over the same time period the researchers saw a 37% decrease in summer sea-ice concentration around the peninsula, and a 4% rise in summer land temperatures.

Previously Walker and his colleagues had hypothesized that the melting sea ice might be causing a rise in land temperatures and encouraging vegetation to grow but this appeared to be only part of the story on the Yamal peninsula. "The linkages between sea-ice decline, land temperatures and NDVI are not as strong on the Yamal as they are in other areas of the Arctic, which led us to examine other factors such as disturbance,"

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