Colloquium: Alexander (“Zan”) Stine

Keman Brothers Postdoctoral Fellow, Harvard Center for the Environment

 

Abstract: The second half of the twentieth century saw a divergence between Arctic temperature and tree-ring reconstructions of that temperature. Arctic vegetation growth is limited not only by temperature but also by light availability, which suggests that 20th century variability in atmospheric transmissivity may be recorded high-latitude tree-ring records. We demonstrate that Arctic tree-ring density is sensitive to explosive volcanic eruptions in proportion to local light limitation upon growth. This light-limitation pattern, taken in conjunction with recent decreases in the intensity of solar shortwave radiation reaching the surface, also explains the pattern of tree-ring divergence. No significant divergence exists in the least light-limited environments, indicating that global dimming is itself sufficient to explain the recent divergence from temperature.