Melting Himalayan glaciers: a big drop in a bucket that’s already full


Anthony Dosseto, University of Wollongong

A new report has warned that even if global warming is held at 1.5℃, we will still lose a third of the glaciers in the Hindu Kush-Himalaya (HKH) region. What does that mean for rivers that flow down these mountains, and the people who depend on them?

The HKH region is home to the tallest mountains on Earth, and also to the source of rivers that sustain close to 2 billion people. These rivers supply agriculture with water and with sediments that fertilise soils in valleys and the floodplain.

Some of these rivers are hugely culturally significant. The Ganges (or Ganga), for instance, which flows for more than 2,525km from the western Himalayas into the Bay of Bengal, is personified in Hinduism as the goddess Gaṅgā.

The Ganga River at Rishikesh, as it exits the Himalayas.
Anthony Dosseto



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When it rains, it pours… literally

Before we get to the effect of melting glaciers on Himalayan rivers, we need to understand where they get their water.

For much of Himalayas, rain falls mostly during the monsoon active between June and September. The monsoon brings heavy rain and often causes devastating floods, such as in northern India in 2013, which forced the evacuation of more than 110,000 people.

2013 floods in Uttarakhand, India.

But the summer monsoon is not the only culprit for devastating floods. Landslides can dam the river, and when this dam bursts it can cause dramatic, unpredictable flooding. Some of those events have been linked to folk stories of floods in many cultures around the world. In the Himalayas, a study tracking the 1,000-year history of large floods showed that heavy rainfall and landslide-dam burst are the main causes.

When they melt, glaciers can also create natural dams, which can then burst and send floods down the valley. In this way, the newly forecast melting poses an acute threat.

The potential problem is worsened still further by the Intergovernmental Panel on Climate Change’s prediction that the frequency of extreme rainfall events will also increase.

Come hell or high water

What will happen to Himalayan rivers when the taps are turned to high in this way? To answer this, we need to look into the past.

For tens of thousands of years, rivers have polished rocks and laid down sediments in the lower valleys of the mountain range. These sediments and rocks tell us the story of how the river behaves when the tap opens or closes.

Rock surfaces tell us where the river was carving into its bed.
Anthony Dosseto

Some experts propose that intense rain tends to trigger landslides, choking the river with sediments which are then dumped in the valleys. Others suggest that the supply of sediments to the river generally doesn’t change much even in extreme rainfall events, and that the main effect of the extra flow is that the river erodes further into its bed.

The most recent work supports the latter theory. It found that 25,000-35,000 years ago, when the monsoon was much weaker than today, sediments were filling up Himalayan valleys. But more recently (3,000-6,000 years ago), rock surfaces were exposed during a period of strong monsoon, illustrating how the river carved into its bed in response to higher rainfall.

Sediments laid down in Himalayan valleys support agriculture, but also tell us the ancient story of rivers that carried them.
Anthony Dosseto

So what does the past tell us about the future of Himalayan rivers? More frequent extreme rainfall events mean more floods, of course. But a stronger monsoon also means rivers will cut deeper into their beds, instead of fertilising Himalayan valleys and the Indo-Gangetic plain with sediments.




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What about glaciers melting? For as long as there are glaciers, this will increase the amount of meltwater in the rivers each spring (until 2060, according the report, after which there won’t be any meltwater to talk about). So this too will contribute to rivers carving into their beds instead of distributing sediments. It will also increase the risk of flooding from outburst of glacial lake dams.

So what is at stake? The melting glaciers? No. Given thousands or millions of years, it seems likely that they will one day return. But on a more meaningful human timescale, what is really at stake is us – our own survival. Global warming is reducing our resources, and making life more perilous along the way. The rivers of the Himalayas are just one more example.The Conversation

Anthony Dosseto, Associate Professor, University of Wollongong

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Himalaya and Hindu Kush Glaciers are Melting


A bird’s eye view of New Zealand’s changing glaciers



File 20180607 137298 1hi3mur.jpg?ixlib=rb 1.1
Small aircraft carry scientists high above the Southern Alps to survey glacier changes.
Hamish McCormick/NIWA, CC BY-SA

Andrew Lorrey, National Institute of Water and Atmospheric Research; Andrew Mackintosh, Victoria University of Wellington, and Brian Anderson, Victoria University of Wellington

Every March, glacier “watchers” take to the skies to photograph snow and ice clinging to high peaks along the length of New Zealand’s Southern Alps.

This flight needs to happen on cloud-free and windless days at the end of summer before new snow paints the glaciers white, obscuring their surface features.

Each year, at the end of summer, scientists monitor glaciers along New Zealand’s Southern Alps.

Summer of records

The summer of 2017-18 was New Zealand’s warmest on record and the Tasman Sea experienced a marine heat wave, with temperatures up to six degrees above normal for several weeks.

The loss of seasonal snow cover and older ice during this extreme summer brings the issue of human-induced climate change into tight focus. The annual flights have been taking place for four decades and the data on end-of-summer snowlines provide crucial evidence.

The disappearance of snow and ice for some of New Zealand’s glaciers is clear and irreversible, at least within our lifetimes. Many glaciers we survey now will simply vanish in the coming decades.

The Franz Josef glacier advanced during the 1980s and 1990s but is now retreating.
Andrew Lorrey/NIWA, CC BY-SA

Glaciers are a beautiful part of New Zealand’s landscape, and important to tourism, but they may not be as prominent in the future. This stored component of the freshwater resource makes contributions to rivers that are used for recreation and irrigation of farm land.

Meltwater flowing from glaciers around Aoraki/Mt Cook into the Mackenzie Basin feeds important national hydroelectricity power schemes. Seasonal meltwater from glaciers can partially mitigate the impacts of summer drought. This buffering capacity may become more crucial if the eastern side of New Zealand’s mountains become drier in a changing climate.

Pioneering glacier monitoring

When Trevor Chinn began studying New Zealand’s 3,000 or so glaciers in the 1960s, he realised monitoring all of them was impossible. He searched for cost-effective ways to learn as much as he could. This resulted in comprehensive glacier mapping and new snow and ice observations when similar work was dying out elsewhere. Mapping of all of the world’s glaciers – nearly 198,000 in total – was only completed in 2012, yet Trevor had already mapped New Zealand’s ice 30 years earlier.

Octogenarian Trevor Chinn still participates in the snowline flights every year to support younger scientists.
Dave Allen/NIWA, CC BY-SA

In addition, he wanted to understand how snow and ice changed from year to year. Trevor decided to do annual glacier photographic flights, looking for the end-of-summer snowlines – a feature about half way between the terminus and the top of a glacier where hard, blue, crevassed glacier ice usually gives way to the previous winter’s snow. The altitude of this transition is an indicator of the annual health of a glacier.

It was a visionary approach that provided a powerful and unique archive of climate variability and change in a remote South Pacific region, far removed from well-known European and North American glaciers. But what was hidden at the time was that New Zealand glaciers were about to undergo significant changes.

Trevor Chinn took part in this summer’s flight and said:

This year is the worst we’ve ever seen. There was so much melt over the summer that more than half the glaciers have lost all the snow they had gained last winter, plus some from the winter before, and there’s rocks sticking out everywhere. The melt-back is phenomenal.

New insights from old observations

The Southern Alps end-of-summer snowline photo archive, produced by the National Institute of Water and Atmospheric Research, is a remarkable long-term record. Our colleagues Lauren Vargo and Huw Horgan are leading the effort to harness this resource with photogrammetry to deliver precise (metre-scale) three-dimensional models of glacier changes since 1978, building directly on Trevor Chinn’s work.

Glaciers respond to natural variability and human-induced changes, and we suspect the latter has become more dominant for our region. During the 1980s and 1990s, while glaciers were largely retreating in other parts of the world, many in New Zealand were advancing. Our recent research shows this anomaly was caused by several concentrated cooler-than-average periods, with Southern Alps air temperature linked to Tasman Sea temperatures directly upwind.

The situation changed after the early 2000s, and we postulated whether more frequent high snowlines and acceleration of ice loss would occur. Since 2010, multiple high snowline years have been observed. In 2011, the iconic Fox Glacier (Te Moeka o Tuawe) and Franz Josef Glacier (Kā Roimata o Hine Hukatere) started a dramatic retreat – losing all of the ground that they regained in the 1990s and more.

In a series of ice collapses, New Zealand’s Fox Glacier retreated by around 300 m between January 2014 and January 2015.

Looking ahead by examining the past

How New Zealand’s glaciers will respond to human-induced climate change is an important question, but the answer is complicated. A recent study suggests human-induced climate warming since about 1990 has been the largest factor driving global glacier decline. For New Zealand, which is significantly influenced by regional variability of the surrounding oceans and atmosphere, the picture is less clear.

To assess how human-induced climate influences and natural variability affect New Zealand glaciers requires the use of climate models, snowline observations and other datasets. Our research team, with support from international colleagues, are doing just that to see how Southern Alps ice will respond to a range of future scenarios.

The ConversationContinuing the snowline photograph work will allow us to better identify climate change tipping points and warning signs for our water resources – and therefore better prepare New Zealand for an uncertain future.

Andrew Lorrey, Principal Scientist & Programme Leader of Climate Observations and Processes, National Institute of Water and Atmospheric Research; Andrew Mackintosh, Professor & Director of Antarctic Research Centre, expert on glaciers and ice sheets, Victoria University of Wellington, and Brian Anderson, Senior Research Fellow, Victoria University of Wellington

This article was originally published on The Conversation. Read the original article.

Don’t worry about the huge Antarctic iceberg – worry about the glaciers behind it


Chen Zhao, University of Tasmania; Christopher Watson, University of Tasmania, and Matt King, University of Tasmania

Icebergs breaking off Antarctica, even massive ones, do not typically concern glaciologists. But the impending birth of a new massive iceberg could be more than business as usual for the frozen continent.

The Larsen C ice shelf, the fourth-largest in Antarctica, has attracted worldwide attention in the lead-up to calving an iceberg one-tenth of its area – or about half the area of greater Melbourne. It is still difficult to predict exactly when it will break free.

But it’s not the size of the iceberg that should be getting attention. Icebergs calve all the time, including the occasional very large one, with nothing to worry about. Icebergs have only a tiny direct effect on sea level.

The calving itself will simply be the birth of another big iceberg. But there is valid concern among scientists that the entire Larsen C ice shelf could become unstable, and eventually break up entirely, with knock-on effects that could take decades to play out.

Ice shelves essentially act as corks in a bottle. Glaciers flow from land towards the sea, and their ice is eventually absorbed into the ice shelf. Removal of the ice shelf causes glaciers to flow faster, increasing the rate at which ice moves from the land into the sea. This has a much larger effect on sea level than iceberg calving does.

While the prediction that Larsen C could become unstable is based partly on physics, it is also based on observations. Using aerial and satellite images, scientists have been able to track very similar ice shelves in the past, some of which have been seen to retreat and collapse.

The death of an ice shelf

The most dramatic ice shelf collapse observed so far is that of Larsen C’s neighbour to the north – the imaginatively named Larsen B. Over the course of just six weeks in 2002 the entire ice shelf splintered into dozens of icebergs. Almost immediately afterwards, the glaciers feeding into it sped up by two to six times. Those glaciers continue to flow faster to this day.

Satellite photo series of Larsen B Ice Shelf collapse from January 2002 to April 2002.
NASA

In our new study, published in Earth and Planetary Science Letters, we turn the clock back even further to look at the Wordie ice shelf, on the west coast of the southern Antarctic Peninsula, which began to retreat in the 1960s and eventually disappeared in January 2017.

Over the past 20 years, observations have shown that the main glacier feeding into the Wordie ice shelf, the Fleming Glacier, has sped up and thinned. Compared with the glaciers feeding Larsen B and C, Fleming Glacier is massive: 80km long, 12km wide, and 600m thick at its front.

Locations of the Larsen C Ice Shelf and the Wordie Ice Shelf-Fleming Glacier system with ice front positions from 1947 to 2016.
Author provided

We used historic aerial photographs from 1966 to create an elevation map of the Fleming Glacier, and compared it to elevation measurements from 2002 to 2015. Between 1966 and 2015 the Fleming Glacier thinned by at least 100m near the front. The thinning rate, which is the elevation change rate, rapidly increased: the thinning rate after 2008 is more than twice that during 2002 to 2008, and four times the average rates from 1966 to 2008.

Ice thinning rate of the Fleming Glacier region during (a) 2002-2008 and (b) 2008-2015.
Author provided

Ice flow speeds have also increased by more than 400m per year at the front since 2008. This is the largest speed change in recent years of any glacier in Antarctica. These changes all point to ice shelf collapse as the cause.

We estimate the total glacier ice volume lost from all glaciers that feed the Wordie is 179 cubic kilometres since 1966, or 319 times the volume of Sydney Harbour. The weight of this ice moving off the land and into the ocean has caused the bedrock beneath the glaciers to lift by more than 50mm.

Other research has suggested this lift could have acted to slow the glacier’s retreat, but it’s clear that the bedrock deformation has not stopped the ice movement speeding up. It seems the Fleming Glacier has a long way to go before it will return to a new stable state (in which snowfall feeding the glacier equals the ice flowing into the oceans).

Fifty years after the Wordie Ice Shelf began to collapse, the major feeding glaciers continue to thin and flow faster than before.

The ConversationWe can’t yet predict the full consequences of the new iceberg calving from Larsen C. But if the ice shelf does begin to retreat or collapse, history tells us it is very possible that its glaciers will flow faster – making yet more sea level rise inevitable.

Chen Zhao, PhD candidate of Antarctic Science, University of Tasmania; Christopher Watson, Senior Lecturer, Surveying and Spatial Sciences, School of Land and Food, University of Tasmania, and Matt King, Professor, Surveying & Spatial Sciences, School of Land and Food, University of Tasmania

This article was originally published on The Conversation. Read the original article.