We wrapped up the latest snowline survey over New Zealand's South Island earlier this month, giving a birds eye view of how glaciers have performed over the past year.
A collection of aerial photos shows the impact of climate change on New Zealand.
New Zealand's glaciers look very thin. The hottest year on record nationwide at the end of 2016 was set off by another Tasman Sea marine heat wave. The pattern continued into the summer of 2022.
As New Zealand's glaciers continue to feel the heat and shrink, bedrock that has not seen daylight for ages becomes exposed. There are basins filled with meltwater. Some of New Zealand's largest lakes are marked by a ring of dirt and rock.
The exposed rocky ridges are being explored to retrace New Zealand's climate history.
The mounds of rocks left behind by retreating glaciers are called moraines. In front of some of the largest glaciers in the Southern Alps, fresh moraines circumscribe turquoise-tinted lakes. There is room for denial of the rapid retreat of ice from the landscape.
Downstream, more extensive moraines are wrapped around massive lake basins that lie along the edge of the Southern Alps. The landforms show ice was much more extensive in the past.
The Mueller, Hooker and Tasman lakes are surrounded by moraines, in Mt Cook National Park. (Andrew Lorrey, CC BY-SA)
The processes that formed those moraines must have been similar to what we see today. How old are they? What happened to the massive ice that was once there?
A new mechanism that explains a rapid shift at the end of the last ice age is based on New Zealand evidence. The new hypothesis is challenging the view that glaciers changed in the recent past.
We think that the Zealandia switch may explain what is happening with our glaciers right now.
(Map: David Barrell, GNS Science; Photos: Aaron Putnam & George Denton, University of Maine, CC BY-SA)
The map shows the ages of the Lake Ohau and Lake Pukaki moraines. moraines show ice rapidly retreated 18,000 years ago.
Glacial geologists use rare chemical isotopes trapped in rocks to trace the history of Earth's surface with a technique called cosmogenic surface exposure dating.
The method shows how long the rocks have been exposed to the rays. Boulders that have been carried inside flowing ice have no exposure history.
When they are dropped onto a moraine and exposed to the rays of outer space, their Cosmic clock starts and the rare isotopes begin to accumulate in the rock.
Exposure dates for moraine boulders are linked to maps that show ice advance and retreat. The major moraines around central Southern Alps lakes have hundreds of results showing rapid change.
The ocean currents and boundaries are visible in the microfossils from the cores. Climate modelling can explain the simultaneous land and sea changes through a major switch of Southern Hemisphere westerly winds over the nearly-submerged Zealandia continent.
The Zealandia Switch helps to promote water vapour export from the tropics and atmospheric circulation patterns that drive warming in both hemispheres. The story about the impact of the Quaternary ice age on global climate, plant ecology and ancient fauna will need to be rewritten if the Zealandia switch hypothesis is upheld.
The southern winds of change are moving again after 18,000 years. Subtropical waters are being pumped into the Tasman Sea, which is driving more frequent marine heatwaves. The temperature in New Zealand is soaring.
Record temperatures are being recorded with the atmospheric rivers loaded with tropical water. The current situation has hallmarks of the Zealandia Switch playing an enhanced role, but this time, Earth is in an interglacial rather than an ice age state.
A rising snowline trend and austral warm season temperatures are tightly coupled. The snowline trend is on the rise.
(Andrew Lorrey, CC BY-SA)
New Zealand's summer snowline has continued to rise in recent years. It is expected to be at least 200m above the 1981-2010 average elevation by next decade.
A series of extremely hot years with high snowlines have been linked to greenhouse gas emissions. Similar conclusions have been drawn for the recent ice loss.
(Reproduced from Lorrey et al. 2022, CC BY-SA)
The snowline is rising in the Southern Alps. Many glaciers monitored by NIWA are expected to be extinct by the year 2035.
It is possible that human activities have moved the Zealandia Switch to a higher level, and it may remain there for the foreseeable future.
We can expect big, fast and global climate re-organization impacts if what unfolds is anything like the Zealandia switch.
The beginning of the end for many glaciers north and south may be brought about by the changes ahead.
Andrew Lorrey is the Principal Scientist of the National Institute of Water and Atmospheric Research.
This article is free to use under a Creative Commons license. The original article is worth a read.
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