New Zealand's Southern Alps glacier melt has doubled

Date:
August 7, 2020
Source:
University of Leeds
Summary:
Glaciers in the Southern Alps of New Zealand have lost more ice
mass since pre-industrial times than remains today, according to
a new study.

The study mapped Southern Alps ice loss from the end of the Little
Ice Age -- roughly 400 years ago -- to 2019. It found that relative
to recent decades, the Southern Alps lost up to 77% of their total
Little Ice Age glacier volume.



FULL STORY ========================================================================== Glaciers in the Southern Alps of New Zealand have lost more ice mass
since pre- industrial times than remains today, according to a new study.


========================================================================== Research led by the University of Leeds, in collaboration with the
National Institute of Water and Atmospheric Research (NIWA) in New
Zealand, mapped Southern Alps ice loss from the end of the Little Ice
Age -- roughly 400 years ago -- to 2019.

The study found that the rate of ice loss has doubled since glaciers
were at their Little Ice Age peak extent. Relative to recent decades, the Southern Alps lost up to 77% of their total Little Ice Age glacier volume.

Climate change has had a significant impact on ice loss around the
world. Not only do local communities depend on glaciers as sources of
fresh water, hydropower and irrigation, but mountain glacier and ice
cap melt presently accounts for 25% of global sea-level rise.

Rapid changes observed today for mountain glaciers need to be put into
a longer-term context to understand global sea-level contributions,
regional climate-glacier systems and local landscape evolution.

The study, published in the journal Scientific Reports, determined
volume changes for 400 mountain glaciers across New Zealand's Southern
Alps for three time periods; the pre-industrial Little Ice Age to 1978,
1978 to 2009 and 2009 to 2019.



==========================================================================
The team reconstructed glacier volumes using historical records of
glacier outlines, as well as examinations of moraines and trimlines,
which are accumulations of glacial debris and clear lines on the side of
a valley formed by a glacier, respectively. Moraines and trimlines can
indicate former ice margin extent and ice thickness changes through time.

By comparing changes in the glacier surface reconstructed during the
Little Ice Age peak and the glacier surface in more recent digital
elevation models, the study found that ice loss has increased two-fold
since the Little Ice Age with a rapid increase in ice volume loss in
the last 40 years.

Up to 17% of the volume that was present at the Little Ice Age was lost
between 1978 and 2019 alone. In 2019, only 12% of ice mass remained in
what was formerly the low altitude part of the Little Ice Age glacier
region -- also called the ablation zone -- and much of the what used
to be ice-covered in the Little Ice Age ablation zone is now completely
ice free.

Study lead author Dr Jonathan Carrivick, from the School of Geography,
said: "These findings quantify a trend in New Zealand's ice loss. The acceleration in the rate of ice mass loss may only get worse as not only climate but also other local effects become more pronounced, such as
more debris accumulating on glaciers surfaces and lakes at the bottom
of glaciers swell, exacerbating melt.

"Our results suggest that the Southern Alps has probably already
passed the time of 'peak water' or the tipping point of glacier melt
supply. Looking forwards, planning must be made for mitigating the
decreased runoff to glacier- fed rivers because that affects local water availability, landscape stability and aquatic ecosystems." Co-author Dr
Andrew Lorrey is a Principal Scientist based at NIWA who was involved with
the study. He says "The long-term ice volume decline, rising snowlines,
and rapid disintegration of glaciers across the Southern Alps we have
observed is alarming. Photographic evidence that has been regularly
collected since the late 1970s show the situation has dramatically
worsened since 2010.

"Our findings provide a conservative baseline for rates of Southern
Alps ice volume change since pre-industrial times. They agree with palaeoclimate reconstructions, early historic evidence and instrumental
records that show our ice is shrinking from a warming climate."

========================================================================== Story Source: Materials provided by University_of_Leeds. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Jonathan L. Carrivick, William H. M. James, Michael Grimes, Jenna L.

Sutherland, Andrew M. Lorrey. Ice thickness and volume changes
across the Southern Alps, New Zealand, from the little ice age
to present.

Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-70276-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200807093750.htm

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