Glaciers spared melting summer
Scientists say temperatures closer to average offered respite but many still in peril
Relative to [surveys in recent years], I’d say the 2020-21 summer was an okay one for many of our glaciers — even offering a bit of respite from more harsh conditions and a string of poor years since 2017. Niwa climate scientist Drew Lorrey
An aerial stocktake has found New Zealand’s glaciers fared better than expected over summer — but the long-term prognosis for the icy wonders remains dire.
Glaciologists last week made their 43rd annual flight over about 50 glaciers across the Southern Alps, some of which have lost millions of cubic metres of ice in the past five years alone.
Over the last four decades, the alps have shed nearly a third of their ice volume — equivalent to the basic daily water use requirements of our current population for that whole period.
Niwa climate scientist Drew Lorrey, who joined other scientists for the Friday fly-over, described current snowlines as being close to “normal” in terms of their altitude.
“But they looked really variable across the range of glaciers we survey,” he added.
“In some cases, the snowline was clear, and in others it was not.”
Ahead of last summer, Lorrey and other scientists aired concerns over the potential impact of La Nina, given the system usually brought hotter, drier conditions to the West Coast.
But the climate driver, which peaked in January, didn’t bring its traditional patterns and appeared to have spared the glaciers its usual melting effects.
“The glaciers looked quite different from 2014, and other recent La Nina years we’ve experienced, where dirty glaciers and a higher-than-normal snowline are typically observed.”
Lorrey said he’d been initially doubtful about seeing any remnant snow cover up in the alpine reaches, until stations in the central alps indicated summer temperatures had actually kept close to average.
“Temperatures leading into the survey this year were not nearly as warm as the lead-in to March 2018 and March 2019, when we had scorching summers ahead of the survey flight,” he said.
“Relative to those recent surveys, I’d say the 2020-21 summer was an okay one for many of our glaciers — even offering a bit of respite from more harsh conditions and a string of poor years since 2017.”
But many had taken a “severe beating” over the past decade, he said — especially smaller ones.
When the renowned glaciologist Dr Trevor Chinn set up the survey in the late 1970s, he travelled as far north as the Kaikoura Ranges, capturing photographic evidence of glaciers in north Canterbury along the way.
In 2018, the team visited some of those sites and decided it was virtually pointless to return to several.
“Some are either in their death throes and past the point of no return or gone altogether.”
One tragic case was the Faerie Queene glacier, in the Spenser Mountains at the southern end of the Nelson Lakes National Park.
“It’s a great example of recent catastrophic ice loss for a small glacier,” he said.
“The combined elements of rising snowlines, warmer temperatures, and expansion of a proglacial lake helped to drive that glacier to collapse.”
Regardless of last season’s bump,
Lorrey pointed out that glaciers took many years to accumulate enough mass of snow and ice to survive over the long-term.
“Normal years, where the balance between snow gain and loss occurs from one season to the next . . . aren’t going to counteract the significant impacts negative mass balance years and ice reduction we’ve experienced recently,” he said.
“The current trajectory of rising temperatures also means we’re going to continue to see our glaciers shrink this century. We will still have ice and some of our largest glaciers, like Tasman Glacier, will survive in one form or another.
“But it’s clear that we do have a role in determining just how much more ice we lose or how much we can keep both in this century and beyond.” — NZ Herald