Mean annual temperature trends and their vertical structure in the tropical Andes

Mean annual temperature trends in the tropical Andes were determined over t he last six decades (1939-1998), to investigate the apparent inconsistency between the observed glacier retreat and the reported slight cooling trend in the lower tropical troposphere after 1979. Our results indicate that tem perature in the tropical Andes has increased by 0.10 degrees - 0.11 degrees C/decade since 1939. The rate of warming has more than tripled over the las t 25 years (0.32 degrees- 0.34 degreesC/decade) and the last two years of t he series, associated with the 1997/98 El Nino, were the wannest of the las t six decades. Temperature trends vary with altitude and show a generally r educed warming with increasing elevation. However, despite the lower rate o f warming, the trend toward increased temperatures is still significant at the 95% confidence level, even at the highest elevations. Clearly high elev ation surface stations in the: Andes do not reflect the slight cooling tren d observed in the tropical lower-troposphere.