New Zealand's glaciers have again suffered one of the worst melts on record, scientists say – and it's doubtful they'll get the top-up they desperately need before summer.

Data being analysed by a team of researchers shows a dismal trend of shrinking glaciers across the Southern Alps only continued during the country's third warmest summer.

Under climate change, many of these icy wonders could vanish completely, while others would become much higher and harder for people to reach.

Being highly sensitive indicators of atmospheric temperature and precipitation levels, glaciers are regarded by scientists as coalmine canaries in a warming world.

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By the numbers