Regional climate control of glaciers in New Zealand and Europe during the pre-industrial Holocene

Mountain glaciers worldwide have undergone net recession over the past century in response to atmospheric warming, but the extent to which this warming reflects natural climate change remains unclear. Knowledge of global patterns of Holocene climate variability provides context for interpreting industrial-age warming and glacier retreat. Between about 11,000 years ago and the nineteenth century, progressive atmospheric cooling over the European Alps induced glacier expansion, culminating with several large-scale advances during the seventeenth to nineteenth centuries. However, it is unclear whether this glacier behavior reflects a global or more regional forcing. Here, we present a ¹⁰Be chronology for glacier fluctuations, and associated temperature variations derived from glacier snowlines, for the past ~11,000 years in the Southern Alps of New Zealand - on the opposite side of the planet from the European Alps. We show that snowlines changed asynchronously in these antipodal regions on orbital as well as sub-millennial timescales. We suggest that such persistent asynchrony resulted from the atmospheric and oceanic effects of migrations of Earth's thermal equator. Thus net glacier recession and atmospheric warming in both regions over the past century is anomalous in the context of detected Holocene changes, and corresponds with the recent addition of fossil CO₂ to the atmosphere.