A period where some of New Zealand's glaciers grew bigger, while those worldwide were shrinking, was likely to have been due to a series of unusually of cold years, according to new research.
At least 58 New Zealand glaciers advanced between 1983 and 2008, with Franz Josef Glacier doing so almost continuously during this time.
Increased rainfall has previously been thought to be the reason.
But a study by Victoria University and Niwa scientists has found that regional climate variability was the likely explanation.
Lead author Associate Professor Andrew Mackintosh says the anomaly between what was happening in New Zealand and the trend overseas hadn't been satisfactory explained.
"So this physics-based study used computer models for the first time to look into it in detail," he said.
"We found that lower temperature caused the glaciers to advance, rather than increased precipitation as previously thought."
Assoc Prof Mackintosh said the reduced temperature was significant enough for the glaciers to grow bigger again in spite of human-induced climate change.
He said the study, published in the scientific journal Nature Communications, found New Zealand glaciers that advanced had certain characteristics, including specific elevation and geometry.
Franz Josef Glacier regained almost half of the total length it had lost in the 20th century.
However, Tasman Glacier, New Zealand's largest and which has about a third of all of the country's ice volume, continued to retreat.
Because of that, New Zealand glaciers lost mass overall over the period.
Assoc Prof Mackintosh said that, although glaciers advancing sounded promising, the future didn't look good.
Since 2008, Franz Josef Glacier had already retreated more than 1.5km.