Working Group II: Impacts, Adaptation and Vulnerability

Other reports in this collection Large-scale atmospheric circulation

Latin America's climate is influenced mainly by the northern Atlantic anticyclone and the migration of the inter-tropical convergence zone, which also affects large areas of tropical South America. The southern part of the continent is more affected by Atlantic and Pacific anticyclones, the thermic low pressure of northwestern Argentina, and mid-latitudes westerlie. All of these circulation features interact strongly with the complex topography of Latin America.

Analysis of ice cores in west Antarctica indicate that meridional atmospheric circulation intensity between middle and high latitudes has experienced substantial strength variability, increasing in the Little Ice Age (Kreutz et al., 1997; Leckenbush and Speth, 1999). At paleoclimatic time scales, analyses of fossilized pollen and lake sediments have shown more intense and frequent incursion of polar air from the Antarctic region 12,000-8,000 years before the present (BP) (Ledru et al., 1994).

In southern Brazil, there has been a tendency over the past 20 years for fewer wintertime cold fronts and polar outbreaks (Marengo and Rogers, 2000), which is somewhat consistent with reported interdecadal variations in the mean position and intensity of the south Atlantic anticyclone (Venegas et al., 1998).

For mid-latitude South America, important changes in zonal circulation have been observed between 1899 and 1986, with wintertime circulation weaker for the period 1939-1949 and strong during 1967-1977—suggesting interdecadal changes. Over Paraguay, southern Brazil, Uruguay, and northeast Argentina, northeasterly circulation associated with the subtropical Atlantic anticyclone increases after 1954 (Hoffman et al., 1987; Minetti and Sierra, 1989; Cantañeda and Barros, 1993; Barros et al., 1999).

Instrumental records, sounding information, and satellite data show changes, fluctuations, and "sudden jumps" in some features of atmospheric circulation over Latin America and its adjacent oceans, in connection with detected changes in the global climate system.

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