Wellington - New Zealand's glaciers have lost 2.2 billion tonnes of permanent ice in the last year and shrunk to their smallest volume since record-keeping began 32 years ago, according to a study published Monday.

"It's one of the clearest signs that our climate is warming," Jim Salinger, principal scientist of the National Institute of Water and Atmospheric Research (NIWA), told reporters.

He said that with a predicted increase in New Zealand's average temperatures of up to 3 degrees Celsius this century, the glaciers would continue to shrink. "It will be difficult for them to grow again," he said.

NIWA has been monitoring 50 glaciers in the Southern Alps for 32 years, and Salinger said that the ice loss in the 12 months ending in March was the fourth highest recorded.

The total remaining ice volume had shrunk by 18 per cent in 20 years and at 44.9 cubic kilometres is now the lowest ever, he said.

"To have that amount of melting, you would have to reduce the precipitation at least by a half or more, or warm a degree," he said.

"We know that precipitation has not gone down in the Southern Alps. In the last quarter of a century it's gone up. So to make them retreat you've got to have more melting, which is higher temperatures. This is certainly a definite sign of warming in the New Zealand area."

Salinger said it was unlikely the glaciers, one of the South Island's biggest tourist attractions, would disappear entirely, as that would require a temperature rise of 7 degrees and no new snow, even at the top of the highest peak in the Alps, Mount Cook (3,754 metres).