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
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.