Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations

M P Lüthi

doi:10.5194/tc-8-639-2014

Abstract

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.

Highlights

Proxy-based climate reconstructions are an important source of information on past climate variability and help to assess whether the climate change presently observed is unprecedented in a long-term context (IPCC, 2007)
Modeled terminus positions calculated with the bestperforming equilibrium line altitude (ELA) histories are compared to the historical records in Fig. 1 (Table 1 for data sources)
This result justifies a posteriori the important assumption that all glacier length changes (GLCs) are caused by the same ELA history

Summary

Introduction

Proxy-based climate reconstructions are an important source of information on past climate variability and help to assess whether the climate change presently observed is unprecedented in a long-term context (IPCC, 2007). Some of these proxies, notably tree-ring data, give a detailed picture of summer temperature variations (e.g., Mann et al, 2009; Büntgen et al, 2006, 2011), while historic records provide more qualitative, but very detailed information (e.g., Pfister, 1999; Casty et al, 2005). GLCs have been used in a qualitative manner to confirm climate reconstructions from other proxies (Guiot et al, 2010) or compare them with solar forcing reconstructions (e.g., Beer et al, 2009; Nussbaumer et al, 2011) Such comparisons suffer from the delayed response of glacier length to climatic or radiative forcing, and are only valid on long timescales. Analytical approximations (Callendar, 1950; Nye, 1963, 1965; Klok and Oerlemans, 2003; Roe and O’Neal, 2009), neural networks (Steiner et al, 2005) and numerical ice flow models (Greuell, 1992; Schmeits and Oerlemans, 1997) have been applied to either single glaciers, an ensemble of glaciers in the same climate region (Oerlemans, 2007), or glaciers distributed around the globe (Hoelzle et al, 2003; Oerlemans, 2005; Leclercq et al, 2011; Leclercq and Oerlemans, 2012)

Results

Discussion

Conclusion