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Climate Change and Debris-Flow Events in Southern Norway
Matthews, J.A., Dahl, S.O., Dresser, P.Q., Berrisford, M.S., Lie, O., Nesje, A. and Owen, G. 2009. Radiocarbon chronology of Holocene colluvial (debris-flow) events at Sletthamn, Jotunheimen, southern Norway: a window on the changing frequency of extreme climatic events and their landscape impact. The Holocene 19: 1107-1129.

Just about everything that goes wrong in the world nowadays is blamed on global warming or the "climate crisis," as Al Gore and his followers like to describe it. And "if global warming is associated with an increase in the frequency of extreme precipitation events" -- as Matthews et al. say "has been inferred from studies over the short term" -- they write in their new study of the subject that "an increase in landscape instability would be expected in response to an increase in frequency of debris flows," which could also be initiated by "the rapid melting of snow or the thawing of frozen ground." But is this simple thinking correct?

What was done
In an effort to explore this question using real-world data, the seven scientists conducted detailed investigations at three alpine slope-foot mires located in the valley of Leirdalen in an area known as Sletthamn, above the treeline among some of the highest mountains in southern Norway, where they say that "exceptionally detailed radiocarbon-dating controlled chronologies of Holocene debris-flow events have been reconstructed," which allowed them to analyze "the frequency and timing of debris flows since c. 8500 cal. BP which, in turn, are related to climatic variability, extreme climatic events and site conditions."

What was learned
Matthews et al. report they could find "no obvious correlation between debris-flow frequency and a relative warm climate." In fact, they say that "debris-flow frequency was lowest post-8000 cal. BP during the Holocene Thermal Maximum," and that most of the "century- to millennial-scale phases of enhanced debris-flow activity appear to correlate with Neoglacial events," one of which was the "Little Ice Age." In addition, they write that "the Sletthamn record agrees quite closely with a compilation of other debris-flow records from widely distributed sites in east and west Norway." What is more -- citing the work of Berrisford and Matthews (1997), Stoffel and Beniston (2006), Pelfini and Santilli (2008) and Stoffel et al. (2008) -- they report that "there appears to be no consistent upward trend in debris-flow frequencies over recent decades," when one might have expected them to be growing in both number and magnitude if climate-alarmist claims were correct.

What it means
The Norwegian and UK researchers conclude that there is little real-world evidence "for the association of higher debris-flow frequencies with an increasingly warm climate." In fact, they say that "the evidence suggests the opposite."

Berrisford, M.S. and Matthews, J.A. 1997. Phases of enhanced rapid mass movement and climate variation during the Holocene: a synthesis. In: Matthews, J.A., Brunsden, D., Frenzel, B., Glaser, B. and Weiss, M.M. (Eds.) Rapid mass movement as a source of climatic evidence for the Holocene. Palaoklimaforschung 19: 409-440.

Pelfini, M. and Santilli, M. 2008. Frequency of debris flows and their relation with precipitation: a case study in the Central Alps, Italy. Geomorphology 101: 721-730.

Stoffel, M. and Beniston, M. 2006. On the incidence of debris flows from the early Little Ice Age to a future greenhouse climate: a case study from the Swiss Alps. Geophysical Research Letters 33: 10.1029/2006GL026805.

Stoffel, M., Conus, D., Grichting, M.A., Lievre, I. and Maitre, G. 20098. Unraveling the patterns of late Holocene debris-flow activity on a cone in the Swiss Alps: chronology, environment and implications for the future. Global and Planetary Change 60: 222-234.

Reviewed 10 March 2010