Abstract
Observational evidence indicates that a number of glaciers have lost mass in the past. Given that glaciers are highly impacted by the surrounding climate, human-influenced global warming may be partly responsible for mass loss. However, previous research studies have been limited to analyzing the past several decades, and it remains unclear whether past glacier mass losses are within the range of natural internal climate variability. Here, we apply an optimal fingerprinting technique to observed and reconstructed mass losses as well as multi-model general circulation model (GCM) simulations of mountain glacier mass to detect and attribute past glacier mass changes. An 8,800-year control simulation of glaciers enabled us to evaluate detectability. The results indicate that human-induced increases in greenhouse gases have contributed to the decreased area-weighted average masses of 85 analyzed glaciers. The effect was larger than the mass increase caused by natural forcing, although the contributions of natural and anthropogenic forcing to decreases in mass varied at the local scale. We also showed that the detection of anthropogenic or natural influences could not be fully attributed when natural internal climate variability was taken into account.
Highlights
The aforementioned previous study compared glacier masses from simulations forced by all known external forcing and only natural forcing, it would be useful to analyze an additional simulation with only anthropogenic forcing to quantify its contributions to past glacier mass
A multivariate regression method of the optimal fingerprinting was applied to the observed and modeled glacier masses to statistically assess the detection quality, taking into account the natural internal climate variations derived from control GCM simulations (CTL) simulations
The contributions of natural and anthropogenic forcing to the change varied among the five glaciers
Summary
The first was an ordinary detection and attribution analysis of a fingerprinting method using direct glacier mass measurements obtained between 1949 and 2003 from the Glacier Mass Balance Bulletin[12] as well as a set of modeled glacier mass using a global glacier model, HYOGA213, forced by the output of GCM experiments. This analysis was conducted for five glaciers in Western Europe, where direct long-term observations of mass balance were available (Supplementary Table S1). We assumed that the control run of a climate model could estimate the distribution of natural internal climate variability[10]
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