A series of unusually cold years in the New Zealand region is responsible for the country’s advancing glaciers, according to a study published in Nature Communications this week. Although this sequence of climate variability and its effect on New Zealand glaciers is unusual on a global scale, it remains consistent with a climate system that is being modified by humans.

The world has experienced unprecedented global ice loss during the past three decades, which were the warmest decades since records began. Despite the warming conditions, some glaciers have grown: in New Zealand, at least 58 glaciers advanced between 1983 and 2008, yet the cause of this growth has been uncertain.

Andrew Mackintosh and colleagues investigate the cause of the anomalous behaviour of New Zealand’s glaciers using a regional-scale energy balance model, which assesses the role of various factors influencing glacier growth or melt. The authors show that the favoured theory - an increase in rainfall - was not supported by their analysis and that instead, cooling in the Tasman Sea and Southern Alps, influenced by large-scale atmospheric waves that encouraged southerly winds in the New Zealand region, was the primary cause. A comparison of model simulations that included and excluded human-induced warming also suggests that Southern Alps glacier ice changes between 1980 and 2005 partly reflects man-made climate change.