Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across the Western Americas

Abstract

Common patterns of climatic variability across the Western Americas are modulated by tropical and extra-tropical oscillatory modes operating at different temporal scales. Interannual climatic variations in the tropics and subtropics of the Western Americas are largely regulated by El Niño-Southern Oscillation (ENSO), whereas decadal-scale variations are induced by long-term Pacific modes of climate variability such as the Pacific Decadal Oscillation (PDO). At higher latitudes, climate variations are dominated by oscillations in the Annular Modes (the Arctic and Antarctic Oscillations) which show both interannual and longer-scale temporal oscillations. Here we use a recently-developed network of tree-ring chronologies to document past climatic variations along the length of the Western Cordilleras. The local and regional characterization of the relationships between climate and tree-growth provide the basis to compare climatic variations in temperature- and precipitation-sensitive records in the Western Americas over the past 3–4 centuries. Upper-elevation records from tree-ring sites in the Gulf of Alaska and Patagonia reveal the occurrence of concurrent decade-scale oscillations in temperature during the last 400 years modulated by PDO. The most recent fluctuation from the cold- to the warm-phase of the PDO in the mid 1970s induced marked changes in tree growth in most extratropical temperature-sensitive chronologies in the Western Cordilleras of both Hemispheres. Common patterns of interannual variations in tree-ring chronologies from the relatively-dry subtropics in western North and South America are largely modulated by ENSO. We used an independent reconstruction of Niño-3 sea surface temperature (SST) to document relationships to tree growth in the southwestern US, the Bolivian Altiplano and Central Chile and also to show strong correlations between these regions. These results further document the strong influence of SSTs in the tropical Pacific as a common forcing of precipitation variations in the subtropical Western America during the past 3–4 centuries. Common patterns of interdecadal or longer-scale variability in tree-ring chronologies from the subarctic and subantarctic regions also suggest common forcings for the annular modes of high-latitude climate variability. A clear separation of the relative influence of tropical versus high-latitude modes of variability is currently difficult to establish: discriminating between tropical and extra-tropical influences on tree growth still remains elusive, particularly in subtropical and temperate regions along our transect. We still need independent reconstructions of tropical and polar modes of climate variability to gain insight into past forcing interactions and the combined effect on climates of the Western Americas. Finally, we also include a series of brief examples (as ‘boxes’) illustrating some of the major regional developments in dendrochronology over this global transect in the last 10 years.