Measuring the Rise and Fall of New Zealand’s Small and Medium Glaciers

Resulting from an unprecedented marine heatwave, the nationwide average temperature in New Zealand for the record-breaking summer of 2017-2018 was 18.1oC, over 2oC above average. Sea surface temperatures varied from 2-4oC above average and even reached 6-7oC above in some areas, the highest temperature anomalies in the world at the time. More, small and medium-sized glaciers in New Zealand’s Southern Alps lost over 13 percent of their total ice volume.

The Southern Alps mountain range, which cuts diagonally across New Zealand’s South Island, is home to over 3,000 small and medium-sized glaciers, which respond to climatic changes––both anthropogenic and natural––much faster than large glaciers. Since the last Little Ice Age ended in 1860, these glaciers in the Southern Alps have notably receded, save for four periods of advancement: around 1950, 1980-1987, 1991-1997, and 2004-2008.

Aerial view of the Southern Alps, New Zealand (Source: Tim Williams/Flickr).

In a new study, published in the International Journal of Climatology, lead researcher Michael J. Salinger of Pennsylvania State University and his co-researchers provide new estimates of glacier ice volume changes and the impact of climate variability on New Zealand’s small and medium-sized glaciers. From 1977 to 2018, the total ice volume of small and medium glaciers went from 26.6 to 17.9 cubic kilometers, a 33 percent decrease.

The researchers utilized a 42-year set of measurements––an annual measurement of the altitude of the end-of-summer-snowline (EOSS)––from 1977 to 2018 to calculate the ice volume changes for a sample of 50 glaciers in the Southern Alps. The EOSS is the boundary between the current year’s new, clean snow and older, dirty snow and is measured in mid to late March, which is the end of New Zealand’s snowy season.

If a particular year experiences lots of melting, the snow line rises in elevation, whereas if snow accumulation exceeds ablation, the snow line will move down. “It’s like doing your annual budget reconciliation,” said Salinger. “So on the 31st of March, [you are] working out whether you’ve received more or less income.”

When researcher and co-author Trevor Chinn started the EOSS monitoring program in 1977, Chinn calculated the volume for all of the over 3,000 glaciers he had mapped. Salinger explained that for this study, the researchers looked at current EOSS elevation compared to years past, using that information to work out the area lost or gained, then convert that to volume of water. “I can work out the glacier contribution from sea level rise, and what I’ve found is that it has been much higher than expected,” he noted.

Valley at an entrance to the snow-covered mountains of the Southern Alps (Source: Richard/Flickr).

Natural climate variability was a primary contributor to interannual fluctuations in glacier ice volume during this time period, even though anthropogenic warming is ultimately responsible for the accelerating downward trend. Volume gains in the 1980s and 1990s were offset and quickly surpassed by rapidly accelerating ice loss from 1998-2018.

The primarily land-covered mid-latitudes of the Northern Hemisphere are much different compared to the mostly ocean-covered midlatitudes of the Southern Hemisphere, which results in strong westerly winds. Salinger cited the Southern Annular Mode (SAM) as the most important source of variability in the Southern Hemisphere. “You can think of the [SAM] as squeezing and relaxing of the westerlies, or the Roaring Forties and Furious Fifties as we call them, over the Southern Ocean,” said Salinger.

In its negative phase, the SAM produces enhanced westerlies, cooler weather, and storm activity. In the positive phase, the strong westerlies move south while westerlies in the mid-latitudes weaken, and the weather gets warmer.

“Temperatures go up and you get less precipitation producing weather and more rain than snow precipitation,” said Salinger. The SAM usually fluctuates between positive and negative phases over weeks to months, but in response to anthropogenic warming, it is becoming increasingly positive.

Salinger noted that to a lesser extent, the El Niño Southern Oscillation also causes interannual climate variability in New Zealand. During an El Niño event, the equatorial easterly trade winds are subject to westerly wind anomalies, which would enhance the negative phase of SAM, leading to even cooler temperatures. La Niña pulls the trade winds in the opposite direction, further weakening westerlies over New Zealand and contributing to more warming.

As anthropogenic warming intensified over the last century, glaciers all around the world retreated, losing ice volume, and contributing to sea level rise. At the same time, natural climate variations happening on interannual and decadal timescales also worked to temporarily offset this massive retreat, even contributing to periodic glacier advances for small and medium-sized glaciers in New Zealand. Ultimately though, glaciers are driven primarily by temperature, and so the impacts of the global warming trend will prevail.

Fox Glacier in the Southern Alps of New Zealand (Source: CameliaTWU/Flickr).

Changing glacier ice volumes throughout New Zealand pose great risks to the country, which relies heavily on hydropower for energy production and on tourism and agriculture for economic output. Salinger cited recent agricultural droughts on the South Island, and the mounting problems faced by farmers without access to irrigation on tap.

Interestingly, New Zealand uses the visual of their rapidly retreating glaciers as an opportunity to raise awareness about climate change. “Our glaciers are iconic, and people are not too far from them, so they are very familiar with them. They’ve seen the huge retreat of some of the glaciers up valleys with melting, because of global warming. It’s something tangible and people can see the long-term change,” said Salinger. “So that’s why we find our glaciers as sort of the canary in the coal mine.”

Read more on GlacierHub:

Photo Friday: New Zealand’s Glacier Retreat from Space

The Curious Case of New Zealand’s Shrinking Glaciers

What the Newest Global Glacier-Volume Estimate Means for High Mountain Asia

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Precipitation Controls Retreat of Kerguelen’s Glaciers

An aerial view of the Kerguelen Islands and its glaciers (Source: NASA Earth Observatory)
An aerial view of the Kerguelen Islands and its glaciers (Source: NASA Earth Observatory)

Islands in the Indian Ocean are not the first to come to mind when glacier retreat is mentioned. However, glaciers in the Kerguelen Islands, located at sub-polar latitudes in the southern hemisphere, have been experiencing widespread and rapid retreat in recent years.

While rising temperatures are generally assumed to be the main cause of glacial retreat, a recent study published in Nature revealed that a reduction in precipitation is the dominant factor controlling the retreat of glaciers in the Cook Ice Cap on the Kerguelen. Similar conclusions were made in a study of Kilimanjaro’s melting glaciers, and this study could offer further insight into the effect of circulation changes on glaciers.

A Macaroni Penguin, one of thirty bird species that nest on the Kerguelen Islands (Source: Magnus Manske).
A Macaroni Penguin, one of thirty bird species that nest on the Kerguelen Islands (Source: Liam Quinn/Wikimedia Commons).

The Kerguelen Islands are among the most isolated places on Earth. Located on the seaway between South Africa and Antarctica, they are only accessible by boat and serve as a nesting ground for many bird species, such as the Macaroni Penguin. Glaciers cover about 500 square kilometers of the islands, and the loss of ice from these glaciers was among the most serious in the world in the 2000s, according to the study mentioned above.

Uncertainty surrounding the effects of climatic changes on glaciers in the southern mid-latitudes is particularly high due to a lack of observational data on glaciers and ice caps. Along with a lack of full modeling studies, this has led to the general assumption that warming is the main driver of glacial loss, as is the case in the northern mid-latitudes.

A team of scientists led by Vincent Favier, a researcher at Université Grenoble Alpes, set out to test the hypothesis that glacial retreat on the Kerguelen was largely due to increasing temperatures. The Cook Ice Cap was a suitable site for study because it is mainly made up of glaciers, which links its mass variations more strongly to climate variations than other ice caps at similar latitudes. In addition,  the availability of long term climate and glaciological observations in the region made it possible to produce accurate models of glacial mass balance from 1850-2011.

A glaciologist uses a steam drill to make a hole in the ice of the Cook Ice Cap to set up an ablation stake (Source: Vincent Favier).
A glaciologist uses a steam drill to make a hole in the ice of the Cook Ice Cap to set up an ablation stake (Source: Vincent Favier).

Using a combination of field data, satellite data, and climate and glacial models, the team was able to attribute 77% of ice loss since the 1960s to atmospheric drying, with temperature increases only amplifying the losses. The researchers used the decade between 1950 and 1960 as a reference period for glacial mass and modelled changes in glacial mass using different hypothetical temperature and precipitation values.

1000 different simulations were run, revealing that dryness is the dominant influence on glacier wastage despite the increase in temperatures in the Kerguelen since the 1960s. The dominant influence of precipitation is particularly evident in glacier mass balance trends between 1963-1975, when both temperatures and mass balance increased. This seemingly paradoxical observation was due to higher levels of precipitation experienced during this period.

Precipitation over the Kerguelen is influenced by the north-south movement of wind belt in the middle latitudes of the Southern Hemisphere – the Southern Annular Mode (SAM). It brings stormy weather to the Kerguelen when it is in a more northerly position, also known as its negative phase. Since 1975, the SAM has been in southerly positions more frequently, increasing atmospheric dryness over the Kerguelen. This is associated with ozone layer depletion and increases in greenhouse gas emissions, suggesting that the frequency of positive phases of SAM is likely to increase over the course of the century and worsen glacier retreat in the Kerguelen.

The terminus of a glacier at the southern end of Cook Ice Cap (Source: B. Navez)
The terminus of a glacier at the southern end of Cook Ice Cap (Source: B. Navez)

Darker surfaces exposed by this loss of glacial ice could exacerbate melting in what is known as the ice-albedo negative feedback mechanism. These surfaces absorb more heat than light colored surfaces like ice, amplifying the effects of temperature changes on glacier loss.

As the SAM is a hemispheric feature, other glaciers within similar latitudes may also have been affected. As Favier explained in an interview with GlacierHub, “We chose this location because we believe it is an example of what is occurring under the same latitude but at other longitudes, in particular in New Zealand… Indeed, this drying trend is suggested at a large scale in the mid latitudes.” However, the lack of long-term sets of observational data for other locations at similar latitudes makes it difficult to determine possible effects, he said.

The difficulty of determining the effects of these changes on other locations within similar latitudes is exacerbated by the poor simulation of temperature and precipitation patterns over the Kerguelen in climate models used by the Intergovermental Panel on Climate Change. 95% of the models used by Favier and his colleagues to model patterns of glacial mass loss in the Kerguelen underestimated glacial mass losses at Cook Ice Cap. As such, projections of ice losses in the southern mid-latitudes based on model simulations should be used with great caution, particularly in areas where circulation changes are expected.

While glacier retreat is usually associated with increasing temperatures, it seems that circulation changes are important too. Remote locations like the Kerguelen Islands can offer clues about some of the impacts of climate change.

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