Holocene mountain glacier fluctuations: A global overview

Abstract

Since one century mountain Holocene glacier fluctuations are considered as proxies of climate changes. Starting from the Alps, studies in all the mountain regions from poles to the equator revealed a multitude of high-frequency glacier fluctuations, mainly related to local-regional climate variability. On the long trend at the millennial scale, a more coherent pattern of glacier advance/retreat phases is emerging, if not worldwide at least at the hemispheric level. In the northern hemisphere mountain glaciers at the beginning of the Holocene were still retreating from Late Glacial positions, but 10 thousand years ago they were already reduced to the present size. From 10 to 5-6 thousand years ago mountain glaciers of the northern hemisphere were mainly reduced to their minimum size, and locally they even entirely disappear. During the last 5-6 millennia mountain glaciers re-expanded, recording several phases of advances, more and more extended and long-lasting, collectively referred to as Neoglaciation. During the last of these phases, known as Little Ice Age (XIV-XIX centuries), mountain glaciers of the northern hemisphere generally reached their maximum extent. As in the previous neoglacial phases, the Little Ice Age consisted of several advances, not exactly comparable (in time and extent) in the different mountain areas. In the southern hemisphere the knowledge is more scanty, with significant differences in humid and in dry areas. Largest advances occurred during the early-mid Holocene, while the Little Ice Age moraines are ubiquitous but often not the more external. During the last century mountain glaciers are retreating all over the world (with some exceptions) at a rate accelerating in the last decades. A few small glaciers are presently reduced to pre-neoglacial size, while larger glaciers, due to decades-long response time, are not yet in equilibrium with present climate conditions.