Evidence for a persistent and extensive greening trend in Eurasia inferred from satellite vegetation index data

The northern latitudes have warmed by ∼0.8°C since the early 1970s, but not all areas have warmed equally. Eurasia shows an overall warming trend, while North America exhibits warming at a lower rate and even a slight cooling trend during the last 50 years in the eastern United States. We analyzed a recently developed satellite normalized difference vegetation index (NDVI) data set (July 1981 to December 1999) to assess vegetation response to these temperature changes. An index of persistence of the NDVI trend was used to generate patches of different levels of persistence. The persistence data were analyzed for patch area, patch perimeter, patch number, patch coherence, largest patch size, patch fragmentation, pixel contiguity, pixel clustering, and conditional probability of pixel adjacency. We address two questions: (1) Is there a difference in the spatial pattern of long‐term NDVI increase in comparison to short‐term increase? and (2) Are there differences in the spatial patterns of patches between Eurasia and North America? The results indicate a persistent and spatially extensive and connected greening trend in Eurasia, relative to North America. The regions showing short‐term greening in Eurasia show a scattered pattern of spatially remote small patches. In North America the long‐term greening pattern is spatially fragmented, and a mixture of short‐ and long‐term NDVI increase is found, unlike in Eurasia. Therefore we conclude that the greening trend in Eurasia is more persistent and spatially extensive than in North America, which is qualitatively consistent with near‐surface air temperature observations.