Unusual Southern Hemisphere Tree Growth Induced by Ozone Depletion

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March 25, 2013

Earth’s climate system includes several patterns of climate variability at the hemispheric scale. One of the best known of these is the El-Nino/Southern Oscillation, which influences weather across much of the globe. Another important feature of the climate system is the Southern Annular Mode (also known as the Antarctic Ocean Oscillation), which is an index of the pressure gradient between the mid- and high-latitudes in the Southern Hemisphere. Over the last few decades, the dominance of the positive phase of the Southern Annular Mode has been increasing. This is due, in large part, to anthropogenic stratospheric ozone depletion. In a study of tree rings across the southern hemisphere over the last few centuries, Dr. Villalba and others found that tree growth over the period 1950-2000 was significantly different than the previous 250 years and that up to half (12-48%) of the variation in tree growth could be explained by variability in the SAM. For example, tree growth was higher than average in the subalpine forests of Tasmania and New Zealand, but lower in the dry forests of Patagonia. Global change biologists tend to focus on the impacts of CO2-induced climate change, but this research reveals other ways anthropogenic emissions can affect affect climate and ecosystems.

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