Recent temperature variations in southern South America

Results from a critical appraisal of surface mean air temperature in Chile and Argentina and extreme air temperature in Chile during the present century are presented. Observations were homogenized to produce a set of time series as reliable as possible. Linear trends computed for the period 1933-1992 resulted in warming rates from 1.3 to 2.0 degrees C 100 years(-1); during the last three decades warming rates are twice as large. The generalized warming is not present around 41 degrees S, where a cooling period from the 1950s to the 1970s prevails. Both positive and negative trends are due mostly to changes in minimum temperatures. The influence of El Nino-Southern Oscillation on surface temperature along the Pacific South American coast from 18 degrees S to 53 degrees S was estimated and found to decrease southward. When its effect is extracted, warming trends become more uniform through time. In particular, the Southern Oscillation Index change around 1976 is felt in minimum temperatures at almost all stations, starting a period with higher values along the Chilean Pacific coast. Trend corrections for autocorrelation in the series introduce only small local changes.