THE CLIMATE CHANGE IN SOUTH AMERICA DUE TO A DOUBLING IN THE CO2 CONCENTRATION: INTERCOMPARISON OF GENERAL CIRCULATION MODEL EQUILIBRIUM EXPERIMENTS

Abstract

Climatic mean sea-level (MSL) pressure, temperature, and precipitation fields simulated by five general circulation models are compared with observations within the area of the South American subcontinent in order to assess their accuracy. Equilibrium climate experiments with doubled atmospheric CO2 concentration are also intercompared to find consistent climate trend patterns in the region. Results are analysed through statistical methods to appreciate the relative model performance at a regional scale. Descriptive analysis is applied to evaluate each model's ability to simulate outstanding climate features. Statistical analysis of control runs indicates comparable and acceptable model performance in seasonal MSL pressure field and surface temperature field simulations, but less satisfactory results in precipitation. Descriptive analysis reveals that some of the local climate characteristics, such as the location of the summer continental warm centre, and the seasonal variation in the mean latitudinal pressure gradient at the southern end of the continent, are not simulated adequately. Regarding precipitation, even those models that perform better in the statistical comparison fail to simulate some of the major precipitation regimes, either in mean magnitude or seasonality of the rainfall rate. Comparison of the 2×CO2 equilibrium experiments allow us to establish some related and physically consistent trend patterns. Among them: (i) a southward shift in two main pressure systems, the summer continental low and the Pacific anticyclone, consistent with a simulated displacement in the arid zone of central Chile and western Argentina, and a noticeable warm-up in the region; (ii) maximum warming in Paraguay and southern Brazil up to the Atlantic coast and concurrent weakening of two pressure systems, the Atlantic anticyclone and the continent al high, during winter; (iii) precipitation increase in the tropical central and eastern part of the continent south of about 15°S, and an opposite trend to the north of this latitude, coincident with a maximum warming in the lower Amazon basin and northern coast of South America, and an intensification of the longitudinal pressure difference between the equatorial Pacific and Atlantic Oceans during summer; (iv) enhanced convective activity in the Inter Tropical Convergence Zone (ITCZ) along the Pacific coast of South America north of the Equator; (v) precipitation increase in the southern end of the continent, consistent with increasing warming at higher latitudes. © 1997 by the Royal Meteorological Society. Int. J. Climatol. 17, 377–398 (1997).