This study analyzed surface temperature trends along the Andes Mountains using over 850 stations in Ecuador, Peru and Chile between 1961-2010. It found that temperatures have generally increased along the Andes, with the strongest warming occurring in earlier decades. However, a cooling trend was observed near sea level along the Pacific coast. The study aimed to determine how much of the overall temperature increase could be attributed to natural climate variability versus human-caused greenhouse gas emissions. It found that climate modes like El Niño and the Pacific Decadal Oscillation influence interannual temperature changes but explain only a small portion of the long-term warming observed.

1. This study investigated the spatiotemporal trends and variability in surface temperature along the Andes using 859 stations in
Ecuador, Peru, and Chile. Glacier mass balance in the region is directly affected by higher temperature, and as regional
temperature has been increasing, glacier retreat has accelerated. Vuille and Bradley (2000) first reported a general trend toward
higher temperatures along the Andes, and highlighted the role of El Niño during extreme warm years. Here we analyze what
fraction of the overall temperature trend is attributed to natural variability of climate modes such as the El Niño-Southern
Oscillation, versus anthropogenic forcing due to emissions of greenhouse gases.
References
Falvey, M., Garreaud, R., 2009. Regional cooling in a warming
world: Recent temperature trends in the southeast Pacific
and along the west coast of subtropical South America (1979-
2006). J. Geophys. Res., 114, D04102,
doi:10.1029/2008JD010519, 2009.
Vuille, M., Bradley, R.S., 2000. Mean annual temperature
trends and their vertical structure in the tropical Andes.
Geophys. Res. Lett. 27, 3885–3888.
Acknowledgements
We would like to thank Rene Garreaud, Bolivar Caceres, and
Waldo Lavado for providing the temperature data.
An Analysis of Surface Temperature
Trends and Variability Along the Andes
Eric Franquist & Mathias Vuille – University at Albany – SUNY, Albany, NY USA
efranquist@albany.edu • mvuille@albany.edu
INTRODUCTION
--85 --80 --75 --70 --65
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1961-1990
Nino3.4Correlation PDOCorrelation SAMCorrelation
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Nino3.4Correlation PDOCorrelation SAMCorrelation
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1981-2010
Nino 3.4Correlation PDOCorrelation SAMCorrelation
<0.0
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Temperature
Trend(K/decade)
Temperaturetrend
(K/decade)attributed
toNino3.4
Temperaturetrend
(K/decade)attributed
toPDO
Temperaturetrend
(K/decade)attributed
toSAM
< -0.3
-- 8 5
1971-2000
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Temperature
Trend(K/decade)
Temperaturetrend
(K/decade)attributed
toNino3.4
Temperaturetrend
(K/decade)attributed
toPDO
Temperaturetrend
(K/decade)attributed
toSAM
<-0.3
--85
1981-2010
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Temperature
Trend(K/decade)
Temperaturetrend
(K/decade)attributed
toNino3.4
Temperaturetrend
(K/decade)attributed
toPDO
Temperaturetrend
(K/decade)attributed
toSAM
<-0.3
--85
Fig. 2 Frequency histograms of temperature
trends using stations with 80% complete data
per time period. Temperature trend is in
°C/decade
Fig. 4 Vertical profiles of temperature trends
in (a) southern, (b) central, and (c) northern
Chile. The upper portion of each graph (white
background) represents the atmosphere and the
lower (blue background) portion represents the
ocean. The solid orange lines are radiosonde
derived trends at 100 m intervals, the lighter
shaded region indicating the 90% confidence
interval (Falvey and Garreaud, 2009).
Fig. 1 Area averaged time series of first difference annual temperatures for 2°N-24°S. Vertical bars extend two
standard errors of the mean on either side of the annual average.
Fig. 5 Correlations between monthly
temperature anomalies and monthly climate
mode anomalies. Stations were only included if
they were at least 80% complete per time period.
Fig. 6 Temperature trend for each station is depicted on far
left, followed by temperature trend attributed to Niño3.4,
PDO, and SAM. Stations were only included if they were at
least 80% complete per time period.
Fig. 3 10°x10° area-averaged temperature
trends, x-axis is temperature trend in °C/decade,
y-axis is latitude.
Summary
Temperatures along the Andes have warmed (Fig. 1), but the warming
has slowed down as compared to previous decades (Fig. 2). A cooling
trend can be observed close to the sea level along the Pacific coast
(Fig. 3), consistent with previous reports from Chile (Fig. 4).
Interannual variability of surface air temperature is driven by natural
modes of climate variability (Fig. 5), but these modes can only
explain a small fraction of the observed warming (Fig. 6).