PP21B-2008: The Bright Side of Tree-Ring Divergence

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Authors: Alexander Stine, Peter Huybers

Author Institutions: Earth & Planetary Sciences, Harvard University, Cambridge, MA, USA

The second half of the twentieth century saw both a decrease in the intensity of solar shortwave radiation reaching the surface of the Earth and 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 a causal relationship between these phenomenon. We demonstrate that Arctic tree-ring density is sensitive to changes in light availability across two distinct phenomena: explosive volcanic eruptions, and the recent epoch of global dimming. In each case the dimmest Arctic regions show the greatest tree-ring density response, whereas the brightest show the least. No significant divergence exists in the least light-limited trees. We repeat this analysis separately for each of the seven species for which we have sufficient data and find, once again, that in all cases divergence increases with increasing light limitation and that divergence approaches zero at the lowest level of light limitation. Changes in light availability thus appear an important control upon tree-ring density and a sufficient explanation for the recent divergence from temperature.

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