New Zealand's Glaciers Are Melting At Twice The Rate Of Pre-Industrial Times

New Zealand's glaciers are a vital source of fresh water for local communities. Jonathan Carrivick, University of Leeds

New research has found that New Zealand’s glaciers are melting faster and faster as time goes by. The study, published in the journal Scientific Reports, reveals that the glacier's rate of ice loss has doubled since pre-industrial times, having now lost around 77 percent of their volume compared to their size during the Little Ice Age.

Climate change is a significant concern for icy landscapes across the globe. Researches from the University of Leeds in collaboration with the National Institute of Water and Atmospheric Research (NIWA) wanted to investigate how temperature-related ice loss had impacted the Southern Alps’ glaciers in recent years, so they mapped the ice loss from the end of the Little Ice Age (around 400 years ago) to 2019. They determined volume changes from ice loss for 400 mountain glaciers across three time periods: the pre-industrial Little Ice Age to 1978, 1978 to 2009 and 2009 to 2019.

Using historical records of glacier outlines and moraines and trimlines, which act like guidelines for the glacier’s previous reach, they calculated the glacier’s historic volumes. By comparing these, they were able to estimate the rate of glacier melt following the Little Ice Age peak and compare it to the rate of ice loss unfolding in the last 40 years.

Comparison of Lyell Glacier in 1866 (A) and in 2018 (B). A Haast, Johann Franz Julius von, 1822-1887/Turnbull Library, Wellington. B  A. Lorrey - NIWA

Their results showed that ice loss has sped up two-fold compared to previous rates of melting, with a rapid increase in ice volume loss in the last four decades. Of the ice volume present during the Little Ice Age, 15 percent of this was lost between 1978 and 2019 alone, a huge increase when you consider this glacier has been melting for around 400 years. In 2019, only 12 percent of the glacier’s historic ice volume remained, demonstrating that if rates continue the glacier could be lost far sooner than expected.

The glacier is of great value to New Zealand, not just as a site of outstanding natural beauty but also as a vital supply of freshwater for local communities. It also provides hydropower and irrigation for the landscape, improving stability and boosting the health of aquatic ecosystems.

Rob Roy glacier in the Matukituki valley in December 2018; this glacier on steep hillslopes is now disconnected from a (out of sight) valley floor part. Jonathan Carrivick, University of Leeds

"These findings quantify a trend in New Zealand's ice loss,” said lead author Dr Jonathan Carrivick, from Leeds' School of Geography, in a statement. “The acceleration in the rate of ice mass loss may only get worse as not only climate but also other local effects become more pronounced, such as more debris accumulating on glacier surfaces and lakes at the bottom of glaciers swell, exacerbating melt.

"Our results suggest that the Southern Alps has probably already passed the time of 'peak water' or the tipping point of glacier melt supply. Looking forwards, planning must be made for mitigating the decreased runoff to glacier-fed rivers because that affects local water availability, landscape stability and aquatic ecosystems."

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