Ricardo Villalba Dr. Ricardo Villalba Department of Dendrochronology & Environmental History IANIGLA-CRICYT Argentina If you would like to interview this scientist, please contact Leah Christen. > biographical information > abstract > paper

Biographical Information:

I graduated from the University of Colorado, Boulder, with a PhD in Physical Geography and currently work at the Snow and Ice Research Institute, in Mendoza, Argentina. In 1996, I moved to Columbia University in New York, where I spent two years as a Lamont-Doherty Fellow. My field of interest is climate changes and their impacts on natural resources, with emphasis on Southern South America. I enjoy my summer fieldwork in the wild and unspoiled forests of Patagonia. During the last years, I have been actively involved in international initiatives related to global change, such as PAGES and the Intergovernmental Panel on Climate Change.

Abstract:

Long-term variability in tropical and high-latitude circulation modes of climate in the Americas

Climate-induced changes in the amount and quality of natural resources are critical determinants of human activities across the Americas. An increasing number of analyses of instrumental data indicate that the climate system fluctuates at many different temporal scales. For example, ENSO and PDO are respectively linked to the interannual- and decadal-scale climatic variability in the tropical Pacific. The dominant modes of climate variability at higher latitudes, such as the Arctic and Antarctic Oscillations, also exhibit short- and long-term modes of variability. Meteorological records are short, severely restricting the study of decadal-scale oscillations and the interactions between interannual and long-term modes of climate variability. High-resolution records (i.e. tree-rings and corals) provide temperature- and precipitation-sensitive records of past climate fluctuations that can be used to examine the temporal and spatial patterns of decadal climatic variability along the western Americas during the past centuries.

A combination of exactly dated tree-ring chronologies from a treeline transect paralleling the western coast of the Americas, and coral records from the tropical Pacific were used to track those past climatic variations in the Pacific that have simultaneously impacted the extratropical regions of North and South America. Significant correlations between temperature reconstructions from Alaska and northern Patagonia with Raratonga Ca/Sr coral-record suggest the existence of an interdecadal oscillatory mode for temperature variations across the Pacific Basin during the past 3-4 centuries. Tree-ring chronologies from precipitation-sensitive regions also reveal interannual- to decadal-scale oscillations, centered at 3.6 and 10-15 years, which have simultaneously influenced climatic conditions in the Midwest-Southern United States, the Bolivian Altiplano and Central Chile. Spatial correlation patterns between tree-ring records and sea surface temperatures (SST) show that variations in climate-sensitive records are strongly connected with SST anomalies in the equatorial Pacific and off the western coast of subtropical America. These correlation patterns resemble the spatial signature of ENSO and PDO over the Pacific. For the past 400 years, striking similarities in temperature fluctuations are observed in the Arctic and sub-Antarctic regions. The most notable feature of temperature change revealed by most high-latitude records is the continuous transition from anomalous cold conditions in the mid-19th century to anomalous warm in the mid-20th century. In contrast, global and hemispheric mean temperatures show almost no trend between the late 1850s to the 1910s, suggesting that high latitudes in both hemispheres share common patterns of temperature changes that may not be present at global scales.

Paper:

Long-term Variability in Tropical and High-latitude Circulation Modes of Climate in the Americas

Climate-induced changes in the amount and quality of natural resources are critical determinants of human activities across the Americas. An increasing number of analyses of instrumental data indicate that the climate system fluctuate at many different temporal scales. For example, ENSO and PDO are respectively linked to the interannual- and decadal-scale climatic variability in the tropical Pacific. The dominant modes of climate variability at higher latitudes, such as the Arctic and Antarctic Oscillations, also exhibit short- and long-term modes of variability. Meteorological records are short, severely restricting the study of decadal-scale oscillations and the interactions between interannual and long-term modes of climate variability. High-resolution records (i.e., tree-rings and corals) provide temperature- and precipitation-sensitive records of past climate fluctuations that can be used to examine the temporal and spatial patterns of decadal climatic variability along the western the Americas during the past centuries.

A combination of exactly dated tree-ring chronologies from a treeline transect paralleling the western coast of the Americas and coral records from the tropical Pacific were used to track those past climatic variations in the Pacific that have simultaneously impacted the extratropical regions of North and South America. Significant correlations between temperature reconstructions from Alaska and northern Patagonia with Raratonga Ca/Sr coral-record suggest the existence of an interdecadal oscillatory mode for temperature variations across the Pacific basin during the past 3-4 centuries.

Tree-ring chronologies from precipitation-sensitive regions also reveal interannual to decadal-scale oscillations, centered at 3.6 and 10-15 years, which have simultaneously influenced climatic conditions in the Midwest-Southern United States, the Bolivian Altiplano and Central Chile. Spatial correlation patterns between tree-ring records and sea surface temperatures (SST) show that variations in climate-sensitive records are strongly connected with SST anomalies in the equatorial Pacific and off the western coast of subtropical America. These correlation patterns resemble the spatial signature of ENSO and PDO over the Pacific. For the past 400 years, striking similarities in temperature fluctuations are observed in the Arctic and sub-Antarctic regions. The most notable feature of temperature change revealed by most high-latitude records is the continuous transition from anomalous cold conditions in the mid-19th century to anomalous warm in the mid-20th century. In contrast, global and hemispheric mean temperatures show almost no trend between the late 1850s to the 1910s, suggesting that high latitudes in both hemispheres share common patterns of temperature changes that may not be present at global scales.

Figure 1. Coherent modes of temperature variability across the Pacific Ocean and Western Americas during the past 4 centuries.
This figure compares temperature-sensitive tree-ring records (red triangles) from high-latitude, Western North and South America with a geochemical coral record (yellow triangle) from Raratonga, tropical South Pacific during the past 3-4 centuries. The series shown from top to bottom are: Spring/Summer Gulf of Alaska temperature reconstruction (1600-1994; Wiles et al., 1998), Sr/Ca coral record from Rarotonga (1726-1996; Linsley et al. 2004) and annual Northern Patagonia temperature reconstruction (1641-1989; Villalba et al., 2003).

Figure 2. Coherent modes of precipitation variability across the Pacific Ocean and Western Americas during the past 4 centuries.
This figure compares precipitation-sensitive tree-ring records across Western America and tropical-/high-latitude forcings of climate variability. The reconstructions of El Niño3 temperature (Mann et al., 2000) and the Mean Sea Level Pressure (MSLP) for the South American-Antarctic Peninsula sector of the Southern Ocean (Villalba et al., 1997) were used as proxies for tropical- and high-latitude forcings of precipitation variations, respectively. The series used for comparison, from top to bottom, are: Tree-ring based PDSI reconstructions from Southwestern United States (SW US) from Cook et al. (2004), a composite Polylepis record including the Caquella and Soniquera chronologies from the Bolivian Altiplano (Argollo et al., 2004), the El Asiento chronology in Central Chile (LeQuesne, personal communication), and the Northern Patagonian precipitation reconstruction (Villalba et al., 1998).