Masiokas, M.H., Villalba, R., Christie, D.A., Betman, E., Luckman, B.H., Le Quesne, C., Prieto, M.R. and Mauget, S. 2012. Snowpack variations since AD 1150 in the Andes of Chile and Argentina (30°-37°S) inferred from rainfall, tree-ring and documentary records. Journal of Geophysical Research 117: 10.1029/2011JD016748.
With all of the hype surrounding climate-alarmist claims of global warming producing more frequent and more extreme manifestations (both negative and positive) of various types of weather phenomena (both negative and positive), the authors write that "the development of robust, statistically-validated models specifically designed to reconstruct Andean snowpack changes over most of the past millennium appears as a necessary and important contribution to evaluate the relative severity of recent observed changes in a long-term context."
What was done
Masiokas et al., as they describe it, "compiled and combined an extensive dataset of different precipitation proxies in an attempt to cross-validate the resulting time series and estimate, as reliably as possible, and extend as far back as possible, the information on winter snow accumulation levels in the central Andes of Chile and Argentina," because of the fact that "the Andean snowpack is the main source of freshwater and arguably the single most important natural resource for the populated, semi-arid regions of central Chile and central-western Argentina." This they did using rainfall data from Chile (which they say are "very strongly correlated with snow accumulation values in the adjacent mountains") to extend a regional 1951-2010 snowpack record back to AD 1866, after which "snow accumulation variations since AD 1150 were inferred from precipitation-sensitive tree-ring series."
What was learned
Based on "an innovative time series analysis approach" that "allowed the identification of the onset, duration and statistical significance of the main intra- to multi-decadal patterns in the reconstructions," the eight researchers determined that "variations observed in the last 60 years are not particularly anomalous when assessed in a multi-century context." In fact, they report that "periods ending in the late 1100s, during the early 1300s and late 1400s, during the early and late 1600s, and during the mid 1700s and mid 1800s appear to have been at least as extreme as the early 20th century period and well above the highest levels seen in recent decades of the instrumental record."
What it means
It most definitely appears that there has been nothing unusual, unnatural or unprecedented about winter snow accumulation in the Andes of Chile and Argentina over the past few decades, when the world's climate alarmists claim the earth warmed to a degree and at a rate that they describe as unprecedented over the past millennium or two.