Tree-ring evidence for tropical-extratropical influences on climate variability along the Andes in South America

VILLALBA, R.

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Lugar: Berna, Suiza; Año: 2007 vol. 15 p. 23 - 25

1563-0803

Instrumental records show that the climate system is characterized by low- and high-latitude modes of variability, which fluctuate at many different temporal scales. The best known is the El Niño-Southern Oscillation (ENSO) phenomenon in the tropical Pacific, which dominates global climate variations on interannual timescales mostly ranging from 3 to 6 years. The Antarctic Oscillation (AAO) is the dominant mode of climate variability at mid- to high latitudes in the southern hemisphere. The positive state of this annular mode is associated with intensified subtropical highs and strong polar lows, which drive a strong extratropical circulation. Interannual-to- decadal variability of climate associated with these atmospheric circulation modes exhibits large spatial and temporal variance that remains poorly documented. Continental- and hemispheric-scale networks of instrumental and proxy climate data are needed to document and help understand these changes in the ocean-atmosphere system. Tree rings represent the most broadly distributed, annually-resolved source of proxy climate data throughout the Andes Cordillera and, thereby, supply the baseline data necessary to evaluate natural climate variability on different temporal and spatial scales. A Collaborative Research Network supported by the Inter-American Institute for Global Change Research (IAI) focused on the development of treeline chronologies from Alaska to Tierra del Fuego. Using a combination of instrumental and tree ring records, the southern component of this study shows how tropical versus extratropical forcings of climate variability influence regional patterns of temperature and precipitation variations from tropical Bolivia (16°S) to sub-Antarctic, southern South America (55°S).