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The time at which climate change signal can be clearly distinguished from noise is known as time of emergence (ToE) and is typically detected by a general circulation model (GCM) signal-to-noise ratio exceeding a certain threshold. ToE is commonly estimated at large scales from GCMs, although management decisions and adaptation strategies are implemented locally. This paper proposes a methodology to estimate ToE for both precipitation and temperature at local scales (i.e., river basin). The methodology considers local climatic conditions and unbiased GCM projections to estimate ToE by using the statistical power to find when the climate significantly differs from the historical one. The method suggests that ToE for temperature already occurred in three Chilean basins (Limarí, Maipo, and Maule). However, in terms of precipitation, an earlier ToE is clearly identified for the Maule basin, indicating that risk assessment and adaptation measures should be implemented first in this basin. [ABSTRACT FROM AUTHOR]

Glacial geologic studies in the Southern Hemisphere (SH) mid-latitudes (40-54°S) indicate renewed glacial activity in southern South America (Patagonia) and New Zealand's (NZ) South Island starting at ∼7 kyr, the so-called neoglaciation. Available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric CO and CH concentrations, lower-than-present but increasing summer insolation and seasonality contrasts. In this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete Paleoclimate Modelling Inter-comparison Project (PMIP2) database of simulations at 6 kyr for the SH. We observe that the amplitude of the annual insolation cycle in the SH did not change significantly at 6 kyr compared to the pre-industrial values, the largest difference occurring in autumn (MAM, negative anomalies) and spring (SON, positive anomalies). The simulated changes in temperatures over the SH respond to the insolation changes, with a 1-2 month delay over the oceans. This results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions, except over Patagonia and NZ, that show a slight increase. In contrast, large-scale circulation features, such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle, as a direct response to the increased/decreased insolation during the transitional seasons SON/MAM. In the annual mean, there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1-3° over the entire SH, which results in a small increase of wind speed over the South Pacific and Atlantic Oceans north of ∼50°S and a widespread decline south of 50°S. PMIP2 simulations for 6 kyr, indicate that in the annual mean, the SH mid-latitudes were colder, wetter and with stronger winds north of about 50°S. These conditions are consistent with the observed neoglacial advances in the region, as well as with terrestrial paleoclimate records from Patagonia that indicate cooling and a multi-millennial rising trend in Southern Westerly Wind intensity starting at ∼7.8 kyr. [ABSTRACT FROM AUTHOR]

This paper discusses the general atmospheric circulation over Patagonia on the basis of the principal palaeoclimate forcings: continental drift, orography, variations in the greenhouse gases in the Earth's atmosphere, evolution of the atmosphere and the oceans, changes in the orbit of the Earth, albedo feedbacks, and the land surface. These processes affect climate on time scales of millions to hundreds of thousands of years. Additionally, orbital forcing has had a major influence on climate during the Quaternary. The palaeo-atmospheric circulation of Patagonia is analyzed for the Early to Late Jurassic, the Cretaceous, the Late Palaeocene-Eocene Thermal Maximum, the Tortonian-Oligocene cooling, the Pliocene, the Quaternary including the Last Glacial Maximum, the Holocene Optimum, and the last millennium changes. Alternative palaeo-atmospheric circulations from climatic modelling scenarios through the ages are reviewed and compared with proxy data. Detailed and updated reference information on the topics analyzed is also provided. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, , 229-249. Este trabajo discute la circulación general de la atmósfera en la Patagonia. Se han explicado los principales forzantes del palaeoclima: deriva continental, orografía, variaciones en los gases de invernadero de la atmósfera terrestre, evolución de la atmósfera y los océanos, cambios orbitales, retroalimentación debida al albedo y las condiciones generales de la superficie terrestre. Estos parámetros afectan el clima en escalas temporales de millones a cientos de miles de años, así como los forzantes orbitales dominaron los cambios climáticos durante el Cuaternario. Las palaeo-circulaciones de la atmósfera sobre Patagonia son analizadas para el Jurásico Temprano y Tardío, el Cretácico, el Máximo Termal del Palaeoceno Tardío- Eoceno, el enfriamiento del Tortoniano- Oligoceno, el Plioceno, y el Cuaternario incluyendo el Último Máximo Glacial (UMG), el Óptimo del Holoceno y los cambios del último milenio. Las palaeo-circulaciones atmosféricas alternativas a través del tiempo a partir de escenarios de modelos climáticos son revisadas y comparadas con proxy datos. Una extensiva lista de referencias provee información detallada y actualizada (Noviembre del 2010) sobre los tópicos analizados en esta publicación. [ABSTRACT FROM AUTHOR]