Tuesday, April 22, 2014

New paper finds Alpine glaciers were of similar size during the Medieval Warm Period

A new paper published in The Cryosphere reconstructs Alpine glacier fluctuations over the past 1600 years and finds glacier lengths of 7 Alpine glaciers were similar during the Medieval Warm Period and the end of the 20th century. 

The paper uses a combination of observations shown as the black dots in Fig 1 below and modeled glacier lengths shown as the red lines. Lengths of the seven modeled glaciers are approximately the same or slightly less during the Medieval Warm Period 1000 years ago as compared to the end of the 20th century:

The author also finds a link between the Atlantic Multidecadal Oscillation [AMO] and reconstructed Alpine summer temperatures and glacier lengths. The AMO, in turn, has been linked to solar activity variation. 

The Cryosphere, 8, 639-650, 2014

M. P. Lüthi
1VAW Glaciology, ETH Zürich, 8093 Zurich, Switzerland
*now at: University of Zürich, 8057 Zurich, Switzerland

Abstract. Mountain glaciers sample a combination of climate fields – temperature, precipitation and radiation – by accumulation and melting of ice. Flow dynamics acts as a transfer function that maps volume changes to a length response of the glacier terminus. Long histories of terminus positions have been assembled for several glaciers in the Alps. Here I analyze terminus position histories from an ensemble of seven glaciers in the Alps with a macroscopic model of glacier dynamics to derive a history of glacier equilibrium line altitude (ELA) for the time span 400–2010 C.E. The resulting climatic reconstruction depends only on records of glacier variations. The reconstructed ELA history is similar to recent reconstructions of Alpine summer temperature and Atlantic Multidecadal Oscillation (AMO) index, but bears little resemblance to reconstructed precipitation variations. Most reconstructed low-ELA periods coincide with large explosive volcano eruptions, hinting at a direct effect of volcanic radiative cooling on mass balance. The glacier advances during the LIA, and the retreat after 1860, can thus be mainly attributed to temperature and volcanic radiative cooling.

1 comment:

  1. Well, the empirical evidence abounds:

    The Mendenhall glacier in Alaska:


    And this clever little "now you see me, now you don't, but I'll be back again" glacier in the Sierra Nevada:


    If these stories, the study here, the stories about higher sea levels in recent eras, etc., were to suddenly widely appear in the main stream media, the debate would be over about dramatic climate change suddenly happening now - caused by anthropogenic causes.

    The broad public must be exposed to the evidence which is right in front of our faces. Only then, will open and intellectual public debates begin to take place.

    Gary H.