Dendroclimatology from regional to continental scales: Understanding regional processes to reconstruct large-scale climatic variations across the Western Americas.

VILLALBA R; LUCKMAN BH; BONINSEGNA J; D'ARRIGO RD; LARA A; VILLANUEVA-DIAZ J; MASIOKAS M; ARGOLLO J; SOLIZ C; LEQUESNE C; STAHLE D; ROIG F; ARAVENA JC; WILES G; JACOBY G; HARTSOUGH P; WILSON RJS; WATSON E; COOK ER; CERANO-PAREDES J; THERRELL M; CLEAVELAND M; MORALES MS; MOYA J; PACAJES J; MASSACCHESI G; BIONDI F; URRUTIA R; MARTINEZ PASTUR G

Dendroclimatology: Progress and Prospects

SPRINGER

Lugar: New York; Año: 2011; p. 175 - 227

Instrumental records show that the climate system is characterized by low- and high-latitudepatterns or modes of variability such as ENSO (El Niño-Southern Oscillation) in the equatorialPacific and the Arctic (AO) and Antarctic (AAO) Oscillations in the extratropics. The Pacific andhigh-latitude atmospheric circulation features associated with interannual to decadal variability ofclimate over the Americas exhibit large spatial and temporal variance that remains poorlydocumented. The resulting regional climate variability has enormous socioeconomic impacts asvividly demonstrated by the disastrous flooding in Paraguay, eastern Argentina and the extendeddrought and massive wildfires in Southwestern US and Mexico during the 1997-1998 El Ninoevent. At decadal scales, the prolonged shift in sea surface temperature patterns over the northand south Pacific Ocean after 1976 (Graham 1994) has resulted in ocean and atmosphericchanges that have caused costly changes in commercial fish populations in the eastern northPacific (Mantua and Hare, 2002; Chavez et al., 2003, Beamish et al., 2004) and a greatly reducedcarrying capacity for commercially important Patagonian grasslands. These coherent interhemisphericchanges in annual and decadal climate patterns appear to have been driven byfundamental changes in the hydrologic cycle of the tropical Pacific Ocean (Graham 1994,Villalba et al., 2001).Hemispheric-scale networks of instrumental and proxy climate data are needed to document andhelp understand these changes in the ocean-atmosphere system and their impact on the Americas.Substantial recent effort has been devoted to the development of ocean-atmospheric monitoringarrays in the tropical Pacific (e.g., TOGA/TAO, TOPEX/POSEIDON, Wallace et al. 1998). Thecost of these arrays has already been justified by the economic benefits provided by the long-leadclimate forecasting associated with recent ENSO warm events. However, there is clearinstrumental and paleoclimatic evidence that, for example, the frequency of warm and coldENSO events has been subject to substantial changes over the past several centuries. Theavailable instrumental meteorological records are simply too short to clearly define the importanttemporal and spatial modes inherent in the low-frequency dynamics of the Pacific and highlatitudemajor circulation systems. As these decade-scale changes in atmospheric circulationhave strong impacts on regional climates and society, understanding these phenomena willimprove the skill of long-range climate forecasting. There is increasing evidence (e.g. Gershunovand Barnett 1998) that they modulate the character of high frequency ENSO events producingmore extreme anomaly patterns when the two systems are “in phase”.4The Western America Cordillera provides a contiguous latitudinal transect of mountainous terrainflanking the world's largest ocean that invites comparative studies of climate variations along theAmericas. The Cordilleras can provide high quality proxy climate records over most of theirlengths. Tree rings provide the most broadly distributed, annually-resolved source of proxyclimate data throughout the Cordillera and thereby supply the comprehensive baseline datanecessary to evaluate natural climate variability on different temporal and spatial scales.Progress in dendroclimatology across the Americas has been concerned with the geographicalexpansion of the research from the local to regional and continental scales. The work of HaroldFritts (1976, 1991) and coworkers in the 1970s represented the first attempt to reconstruct thepatterns of spatial variation in temperature, precipitation and atmospheric pressure across NorthAmerica and the Pacific Ocean, based on 65 ring-with chronologies from the western UnitedStates. Collaborative work between several research groups during the past 10 years (Meko et al,1993; Cook et al. 1999, 2004) have extended this methodology by compiling 835 chronologiesfrom Canada, United States and Mexico to reconstruct a gridded network of 297 summer PalmerDrought Severity Indices across North America that spans the past 500-600 years (or longer) overmuch of the grid (Cook et al., 2004). Following these initiatives, new projects have continued todevelop databases of tree-ring chronologies that cover large areas in the Western Americas (Fig.1).One of the Collaborative Research Networks supported by the Inter-American Institute forGlobal Change Research (IAI) was focused around the development of treeline chronologiesfrom Alaska to Tierra del Fuego (Luckman and Boninsegna, 2001). Using this as a frameworkwe discuss in this chapter some of the most significant developments in tree-ring research acrossthe Western Americas, reviewing local- and regional-scale studies and how they contribute to ourunderstanding of present and past variations in the circulation modes of climate variability atcontinental and inter-hemispheric scales. The Western Cordillera of the Americas run transverseto the generally latitudinal organization of the major climate-ocean circulation systems andtherefore past variations in the major modes of general circulation dynamics linked to El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), the Arctic (AO) and Antarctic(AAO) oscillations can be investigated using tree-ring records from this global scale transect.