The retreat of the world's glaciers
Rivers of ice
Ice ages have come and gone, vast ice sheets expanding and contracting across the temperate latitudes, but through it all, glaciers have continued on their planet-altering ways, gouging out great valleys as they slowly flow downhill. Today, they cover around ten per cent of the Earth’s land surface, but thanks to global warming, they are in peril.
There are two zones along a glacier: the accumulation zone and the ablation zone. The accumulation zone is where the mass of the glacier accumulates. Ice is lost, in the ablation zone, through melting, sublimation (when ice turns to water vapour in a single step) and, where glaciers enter lakes or the ocean, the calving off of icebergs.
Healthy glaciers are like healthy bank accounts. The amount of income, in the form of snow, equals or exceeds the amount of outgoings, in the form of melting, sublimation and calving. In an unhealthy glacier, the addition of new snow doesn’t keep up with the rate at which ice is lost, and as a result, the glacier loses ice volume, which is usually expressed as the retreat of the glacier’s terminus or tongue.
Glaciers are vital at two different levels – what they are and what they indicate. They are massive reservoirs of fresh water that feed rivers around the world and they indicate the true extent of climate change. ‘We perceive that glaciers are especially sensitive to global climate change because they are highly dynamic and visible features,’ says Dr Jonathan Carrivick of the University of Leeds.
Going, going...
Glacier retreat is nothing new. ‘If you look historically at all glaciers globally, they have been retreating fairly linearly since the end of the Little Ice Age about 150 years ago, although certain decades do buck the trend,’ says Dr Alun Hubbard of Aberystwyth University.
A 2005 study of historical records of glacier length showed that for the period between 1860 and 1900, 35 of the 36 glaciers for which records were available retreated; for 1900–80, 142 of 144 glaciers retreated.
The problem now is the speed and the widespread nature of the retreat. In a recent study of 100 glaciers in Alaska and Canada, all but three were losing mass. When the Glacier National Park in the USA was originally demarcated in 1910, it contained a total of 150 glaciers. There are now around 50, and modelling carried out by the US Geological Survey predicts that ‘all glaciers in the basin will disappear by the year 2030, despite predicted increases in precipitation’.
According to one current prediction, all of the glaciers in the Himalaya could disappear by 2035. Switzerland’s 1,800 glaciers, which cover a total area of around 3,000 square kilometres and provide the water that generates half of the country’s electricity, could disappear completely by 2080 if current trends continue. The International Panel on Climate Change (IPCC) quotes models that indicate that between a third and a half of the world’s existing mountain glacier mass could disappear within the next 100 years.
The World Glacier Monitoring Service (WGMS) – which closely monitors 30 glaciers in nine mountain ranges, including the Andes, the Alps, the Rockies and the Altai – has just published preview data from 2004 and 2005. The conclusion is stark: ‘The reported period has been extreme and without precedence in
the European Alps, where new record mass losses exceeded earlier record values by at least another 50 per cent. This, together with strongly negative balance values in Scandinavia and western North America, created a new record of annual mass loss in almost a quarter of a century of documentation in the Glacier Mass Balance Bulletin.’
So why are glaciers disappearing? ‘A combination of accelerated atmospheric and oceanic warming in the past few decades,’ says Hubbard.
‘Small alpine glaciers and those in maritime locations (for example, Norway and western New Zealand) have exceptionally high mass turnovers, which are driven by fluctuations in
air temperature and/or precipitation,’ explains Carrivick. ‘Just a small temperature change (1°C, for example) or precipitation change can have dramatic consequences for the annual budget of a glacier system. Antarctic glaciers, on the other hand, particularly those on the Antarctic Peninsula, appear to be sensitive because they are at low altitude and are buttressed by ice shelves that can break up due to changes in sea level or sea temperature.’
And the ice loss is accelerating. During the late 1990s, data from airborne surveys of many of Alaska’s glaciers were compared to ground surveys from the mid-1950s. The results showed that in the four decades leading up to 1995, the glaciers lost a total of 57 cubic kilometres (gigatonnes) of ice per year; between 1995 and 2000–01, the rate of ice loss nearly doubled to 105 cubic kilometres per year.
Similarly, according to the WGMS, for the glaciers it monitors, the average annual ice loss since 2000 was about 0.6 metres, which is 1.6 times more than the average for the 1990s and three times the loss rate of the 1980s.
‘Glaciers tend to be found in the high-altitude and high-latitude environments, which are currently experiencing the fastest temperature changes under global warming,’ says Hubbard. Hence the observed accelerated losses in regions such as Alaska, Greenland, the Antarctic Peninsula, Patagonia and the Alps.
‘Glaciers in these regions really are the “canaries down the coalmine”, he says. ‘They are very sensitive to change and they are experiencing very rapid climate shifts. For example, over the past 50 years, there has been an almost 4°C warming over the Antarctic Peninsula, which has led to around 90 per cent of the glaciers there going into retreat.’
Not a drop to drink
Although they only hold less than two per cent of the world’s water, glaciers hold the majority of the fresh water: nearly 70 per cent of it. The annual cycle of spring and summer melting brings relief for many areas with highly seasonal rainfall patterns. Estimates vary, but as many as two billion people could rely on glaciers for much of their freshwater supply. In addition, this water is important for industry, agriculture and electricity generation.
With more than 30,000 square kilometres of glaciers, the Himalaya has been described as the ‘Water Tower of Asia’. The annual cycle of melting sees these glaciers feed around 8.6 million cubic metres of water into a collection of rivers that includes seven of Asia’s most important: the Ganges, Indus, Brahmaputra, Salween, Mekong, Yangtze and Huang He. Indeed, almost 70 per cent of the discharge to the River Ganges comes from Nepalese snow-fed rivers. So, if the Himalayan glaciers disappear, these mighty rivers could dry up for at least part of the year.
In Africa, the famous white mantle of Kilimanjaro, the world’s only equatorial glacier, has shrunk by more than 80 per cent since 1912. As a result, a number of rivers in Tanzania have dried up.
Two million people living in the Bolivian capital, La Paz, and one of its suburbs, El Alto, get about a third of their drinking water from glaciers whose area has shrunk by more than half since the 1960s, according to Walter Vergara, a World Bank expert on climate change in Latin America.
Where detailed studies have been undertaken, it has been shown that glacial run-off can account for almost half of a river’s annual flow. The IPCC predicts that as temperatures increase, so, too, will the rate of snowmelt. This will be coupled with a reduction in the amount of snowfall as winter is shortened.
To begin with, this may not be noted as a problem, as the glaciers will provide the rivers with more water as the ice disappears. The increase will be dramatic. In Central Asia,
for example, there is an anticipated threefold increase by 2050. However, this can’t last forever and it’s estimated that by 2100, run-off will have reduced to two thirds of present-day volume. Already, dry season water resources are under stress, and demand continues to increase, so any reduction in glacial flow could potentially lead to widespread hardship for those who rely on glacial run-off for their water supply, which could in turn, create geopolitical tension.
In Kazakhstan, for example, there is a looming crisis that has been highlighted by the work of Stephan Harrison from Exeter University. ‘The former capital of Almaty in the southeast has two sources of water for its people, agriculture and industry,’ he says. ‘There is the River Ili, which flows in from China and is potentially going to be much reduced in volume as dams and diversions are erected to meet China’s needs. And then there is the one local source from the glaciated Bolshaya and Malaya Almatinka drainage basins lying 30 kilometres south of Almaty.’
Harrison’s study has drawn on an invaluable historical resource: the Tuyuksu glacier in the Malaya Almatinka valley has been monitored since 1879. ‘It’s clear that they are melting rapidly,’ Harrison says. ‘Between 1955 and 2000, the glaciers have lost around 0.7 per cent of their mass per year. Over this period, the glaciers reduced their total surface area from 272 to 201 square kilometres.’
As the glaciers melt, the residents of Almaty will come to rely more and more on water from the River Ili, undoubtedly leading to tensions with China.
Looming catastrophes
However, there is a more dramatic problem. As glaciers melt, the meltwater is often held back by a mass of moraine, debris left behind by the retreating glacier. This leads to the formation of a glacial lake, and the rapid rate at which many glaciers are now melting is leading some of these lakes to grow extremely quickly. Researchers have found that retreating glaciers can help fill glacial lakes so rapidly that their area can grow by 350 per cent in just 15 years; some glacial lakes in Nepal have grown to almost eight
times the size they were during the 1970s.
The natural dams holding all of this water in are very unstable, and when they break, the so-called glacial lake outburst floods (GLOFs) that result can be devastating, involving the sudden release of hundreds of millions of cubic metres of water.
Between 1977 and 1998, five GLOF events occurred in Nepal. One of the best documented took place on 4 August 1985, when a large chunk of ice broke from the upper section of
the Langmoche glacier in the country’s east and splashed into Dig Tsho glacial lake, causing the lake to break through its 50-metre bank of ice and moraine and releasing ten million cubic metres of water in three hours. The resultant floodwaters rose up to 15 metres in height and the effects were felt more than 90 kilometres downstream. Thirty houses, 14 bridges and US$4million worth of cultivated farmland were destroyed, as was the almost completed US$1.5million Namche Small Hydropower Project.
Of the 3,250 Himalayan glaciers in Nepal, 2,315 contain glacial lakes that are currently increasing in size. For example, Tsho Rolpa in the Rolwaling valley is now six times larger than it was during the 1950s. The lake represents a serious risk to the people, livestock, property and infrastructure of the village of Tribeni, which is located 108 kilometres downstream and has a population of 10,000 people.
Nepal isn’t the only country facing such threats. In Bhutan, there have already been two catastrophic outburst floods. In 1994, a lake burst free in the Lunana area, killing 21 people, washing away bridges and leaving the valley filled with debris and logs. A report produced earlier this year by the International Centre for Integrated Mountain Development identified 20 potentially dangerous glacial lakes in Nepal and 24 in Bhutan.
And it isn’t just the Himalayan glaciers that present such a threat to life. In July 1998, a GLOF in the Shahimardan valley of Kyrgyzstan and Uzbekistan killed more than 100 people. Another in August 2002 in the Shakhdara valley of the Tajik Pamir mountains claimed 23 lives. And in Peru, it has been estimated that 32,000 people were killed by GLOF events during the 20th century. For example, in 1941, a chunk of ice falling into Lake Palcacocha triggered a flood that killed 7,000 people. Recent satellite photos have revealed that another chunk of ice is poised above the lake, potentially threatening the lives of 100,000 people living in the valley below.
Rising tide
However glaciers lose their ice, whether by calving or melting, the water eventually ends up in the ocean. A number of different models have predicted what effect this will have on sea levels. Scientists at the National Snow and Ice Data Centre, based at the University of Colorado, have estimated that if all of the world’s ice fields and glaciers were to melt, global sea levels would rise by 70 metres.
However, such a scenario is unlikely to take place for several centuries. In the meantime, it’s the demise of some of the world’s smaller glaciers that should have us concerned. In a recent paper published in Science, a team led by Mark Meier of the University of Colorado predicted a 24-centimetre rise in sea level by 2100 from small glaciers alone. When this is combined with the gradual thaw of Greenland and Antarctica, Meier estimates that levels will rise by 56 centimetres, just from ice melt.
(This may not sound like much, but you have to take into account the fact that a 30-centimetre rise in sea level will typically lead to a retreat in the shoreline of 30 metres or more. Some 100 million people currently live within the equivalent of about a metre’s rise in sea level.)
The input of all of that cold fresh water is also likely to cause major shifts in ocean and atmosphere circulation, according to Hubbard. The exact nature of those shifts is still the subject of intense debate among geographers.
Special conditions
While the evidence of glacial retreat is overwhelming, and the argument for blaming global warming seemingly watertight, we must still avoid making simplistic assumptions about bigger issues from the misreading of the evidence presented by glaciers.
An important case study is Kilimanjaro. The highest mountain in Africa, near the equator in Tanzania, is famous for the glaciers at its peak. These have been disappearing at an alarming rate; in the past 100 years, 90 per cent of the ice has disappeared, and there have been predictions that the mountain will have completely lost its ice cover by 2020.
Ice core studies on Kilimanjaro have revealed frozen organic matter from 9,000 years ago, suggesting that the glaciers have been in place at least that long. So what has caused the rapid retreat? Environmentalists have leapt on the iconic mountain as symbolic of the fate of glaciers and ice sheets around the globe. But has the ice been melting because of anthropogenic climate change?
Not according to Austrian glaciologist Georg Kaser. He argues that conditions on Kilimanjaro are special, and that the loss of ice is explained by reduced rainfall in the region, creating a drier environment that allows sublimation to take place. Kaser isn’t a climate-change denier, but he believes that Kilimanjaro ‘is not an appropriate poster child for global climate change’.
The example of Kilimanjaro illustrates the complexity of both glacial systems themselves and the way in which they respond to climatic changes. ‘Glacier response isn’t straightforward,’ says Hubbard. ‘It’s complicated by a number of other factors that may dampen or amplify that response. These factors include the configuration and shape of the landscape in which the glacier sits (steep glaciers tend to respond more rapidly but less extensively than low-gradient ones), the mechanics and the dynamics at the base of the glacier – if the ice melting at the surface reaches the glacier bed, it tends to accelerate the glacier flow and hence its response to climate warming.
‘Glaciers also respond to nuances in the seasonal climate,’ he continues. ‘Across Europe, the 1970s tended to be a time of shorter summers, with the onset of ‘winter’ taking place much earlier than it does now and with more precipitation – snow in September, for example. It isn’t well known that more than half of the glaciers in the Swiss Alps were advancing during the 1970s.’
Even today, many of the world’s glaciers are holding their own and, paradoxically, about ten per cent are actually increasing in size.
A March 2005 survey of 50 glaciers in New Zealand by the National Institute of Water and Atmospheric Research (NIWA) found that on average, the glaciers in New Zealand’s Southern Alps had gained considerably more ice than they had lost during the previous year. The gains were due to increased snow in the Southern Alps, particularly from late winter to early summer of the previous year, at which time temperatures were 0.6°C below average, producing more snow. ‘Over the past three years, the glaciers have gained in mass, halting the declines seen between 1998 and 2002,’ said NIWA principal scientist Dr Jim Salinger at the time. ‘This past year was the seventh-largest gain since we started aerial surveys in 1977.’
Similarly, a number of glaciers in Pakistan’s Upper Indus River Basin have been growing. Although meteorological data show that winter temperatures have been rising in parts of the Western Himalaya, Karakoram and Hindu Kush mountain ranges, the region’s winter snowfall has also been on the rise. And the average summer temperatures have been dropping, reducing the rate of melting.
Do these examples provide a glimmer of hope that the doom-mongers might have been wrong? Unfortunately not. In fact, they provide further support to the contention that the planet is in the process of great climatic change. Warming can generate more precipitation and this can fall as snow on glaciers, contributing to their growth.
Mount Shasta, the fifth-highest mountain in California, is a case in point. In 2002, Slawek Tulaczyk and Ian Howat of the University of California, Santa Cruz, undertook the first detailed survey of the mountain’s glaciers in 50 years. To their surprise, they found not retreat, but growth. The tongue of the Whitney Glacier, for example, is moving forward at around ten centimetres per day. In the past 50 years, the glacier has expanded by almost a third, the only glacier in the world known to be larger than it was in 1890, at the height of the Little Ice Age.
The researchers suspect that the growth is actually the result of global warming. Shasta is part of the Cascade Range, which runs down the USA’s west coast. Increases in temperature of the air over the Pacific Ocean has meant that it’s able to carry more moisture, which then falls on Shasta’s glaciers as snow. The annual snowfall that the mountain receives currently exceeds the summer melt by as much as 40 per cent.
And things can change quickly. During the late 1990s, it was reported that numerous glaciers in Norway and Sweden were growing at unprecedented rates. Again, this was down
to changing patterns of precipitation. Not long after, a further rise in air temperature saw the glaciers begin to retreat.
Serious threat
Glaciers are contradictory. They allow people to live when the rains don’t fall, yet they threaten the very lives of the people they nurture. Perhaps they are more important than we imagine – as they offer so distinct and clear an indication of changes in our climate, they might just be charismatic enough to get more people
to take the threat seriously: because if we don’t, these mighty water towers will vanish and we will all feel the consequences.
Two-minute warning
If a 15-metre-high wall of water was hurtling down a river valley towards your village, you would want to know about it. And with such a scenario becoming increasingly likely as glaciers melt and glacial lakes grow, numerous organisations are setting up glacial lake outburst flood (GLOF) early warning systems designed
to detect impending GLOFs in sufficient time to relay a warning to those who might be affected so they can move to safer ground.
Nepal’s Department of Hydrology and Meteorology has installed an early warning system in the villages of the Tama Koshi valley, which are threatened by Tsho Rolpa glacial lake. Six water-level sensors have been installed in the river channel immediately downstream of the lake outlet. Armoured and shielded cables connect the sensors to a transmitter station located about 80 metres away, higher up the slope.
Within two minutes of the initiation of a flood, the system will immediately set off warning stations in the villages, which consist of an air-powered horn backed up by an electric horn. The entire warning system is fully automated, redundant and requires no human intervention.
December 2007
Ice ages have come and gone, vast ice sheets expanding and contracting across the temperate latitudes, but through it all, glaciers have continued on their planet-altering ways, gouging out great valleys as they slowly flow downhill. Today, they cover around ten per cent of the Earth’s land surface, but thanks to global warming, they are in peril.
There are two zones along a glacier: the accumulation zone and the ablation zone. The accumulation zone is where the mass of the glacier accumulates. Ice is lost, in the ablation zone, through melting, sublimation (when ice turns to water vapour in a single step) and, where glaciers enter lakes or the ocean, the calving off of icebergs.
Healthy glaciers are like healthy bank accounts. The amount of income, in the form of snow, equals or exceeds the amount of outgoings, in the form of melting, sublimation and calving. In an unhealthy glacier, the addition of new snow doesn’t keep up with the rate at which ice is lost, and as a result, the glacier loses ice volume, which is usually expressed as the retreat of the glacier’s terminus or tongue.
Glaciers are vital at two different levels – what they are and what they indicate. They are massive reservoirs of fresh water that feed rivers around the world and they indicate the true extent of climate change. ‘We perceive that glaciers are especially sensitive to global climate change because they are highly dynamic and visible features,’ says Dr Jonathan Carrivick of the University of Leeds.
Going, going...
Glacier retreat is nothing new. ‘If you look historically at all glaciers globally, they have been retreating fairly linearly since the end of the Little Ice Age about 150 years ago, although certain decades do buck the trend,’ says Dr Alun Hubbard of Aberystwyth University.
A 2005 study of historical records of glacier length showed that for the period between 1860 and 1900, 35 of the 36 glaciers for which records were available retreated; for 1900–80, 142 of 144 glaciers retreated.
The problem now is the speed and the widespread nature of the retreat. In a recent study of 100 glaciers in Alaska and Canada, all but three were losing mass. When the Glacier National Park in the USA was originally demarcated in 1910, it contained a total of 150 glaciers. There are now around 50, and modelling carried out by the US Geological Survey predicts that ‘all glaciers in the basin will disappear by the year 2030, despite predicted increases in precipitation’.
According to one current prediction, all of the glaciers in the Himalaya could disappear by 2035. Switzerland’s 1,800 glaciers, which cover a total area of around 3,000 square kilometres and provide the water that generates half of the country’s electricity, could disappear completely by 2080 if current trends continue. The International Panel on Climate Change (IPCC) quotes models that indicate that between a third and a half of the world’s existing mountain glacier mass could disappear within the next 100 years.
The World Glacier Monitoring Service (WGMS) – which closely monitors 30 glaciers in nine mountain ranges, including the Andes, the Alps, the Rockies and the Altai – has just published preview data from 2004 and 2005. The conclusion is stark: ‘The reported period has been extreme and without precedence in
the European Alps, where new record mass losses exceeded earlier record values by at least another 50 per cent. This, together with strongly negative balance values in Scandinavia and western North America, created a new record of annual mass loss in almost a quarter of a century of documentation in the Glacier Mass Balance Bulletin.’
So why are glaciers disappearing? ‘A combination of accelerated atmospheric and oceanic warming in the past few decades,’ says Hubbard.
‘Small alpine glaciers and those in maritime locations (for example, Norway and western New Zealand) have exceptionally high mass turnovers, which are driven by fluctuations in
air temperature and/or precipitation,’ explains Carrivick. ‘Just a small temperature change (1°C, for example) or precipitation change can have dramatic consequences for the annual budget of a glacier system. Antarctic glaciers, on the other hand, particularly those on the Antarctic Peninsula, appear to be sensitive because they are at low altitude and are buttressed by ice shelves that can break up due to changes in sea level or sea temperature.’
And the ice loss is accelerating. During the late 1990s, data from airborne surveys of many of Alaska’s glaciers were compared to ground surveys from the mid-1950s. The results showed that in the four decades leading up to 1995, the glaciers lost a total of 57 cubic kilometres (gigatonnes) of ice per year; between 1995 and 2000–01, the rate of ice loss nearly doubled to 105 cubic kilometres per year.
Similarly, according to the WGMS, for the glaciers it monitors, the average annual ice loss since 2000 was about 0.6 metres, which is 1.6 times more than the average for the 1990s and three times the loss rate of the 1980s.
‘Glaciers tend to be found in the high-altitude and high-latitude environments, which are currently experiencing the fastest temperature changes under global warming,’ says Hubbard. Hence the observed accelerated losses in regions such as Alaska, Greenland, the Antarctic Peninsula, Patagonia and the Alps.
‘Glaciers in these regions really are the “canaries down the coalmine”, he says. ‘They are very sensitive to change and they are experiencing very rapid climate shifts. For example, over the past 50 years, there has been an almost 4°C warming over the Antarctic Peninsula, which has led to around 90 per cent of the glaciers there going into retreat.’
Not a drop to drink
Although they only hold less than two per cent of the world’s water, glaciers hold the majority of the fresh water: nearly 70 per cent of it. The annual cycle of spring and summer melting brings relief for many areas with highly seasonal rainfall patterns. Estimates vary, but as many as two billion people could rely on glaciers for much of their freshwater supply. In addition, this water is important for industry, agriculture and electricity generation.
With more than 30,000 square kilometres of glaciers, the Himalaya has been described as the ‘Water Tower of Asia’. The annual cycle of melting sees these glaciers feed around 8.6 million cubic metres of water into a collection of rivers that includes seven of Asia’s most important: the Ganges, Indus, Brahmaputra, Salween, Mekong, Yangtze and Huang He. Indeed, almost 70 per cent of the discharge to the River Ganges comes from Nepalese snow-fed rivers. So, if the Himalayan glaciers disappear, these mighty rivers could dry up for at least part of the year.
In Africa, the famous white mantle of Kilimanjaro, the world’s only equatorial glacier, has shrunk by more than 80 per cent since 1912. As a result, a number of rivers in Tanzania have dried up.
Two million people living in the Bolivian capital, La Paz, and one of its suburbs, El Alto, get about a third of their drinking water from glaciers whose area has shrunk by more than half since the 1960s, according to Walter Vergara, a World Bank expert on climate change in Latin America.
Where detailed studies have been undertaken, it has been shown that glacial run-off can account for almost half of a river’s annual flow. The IPCC predicts that as temperatures increase, so, too, will the rate of snowmelt. This will be coupled with a reduction in the amount of snowfall as winter is shortened.
To begin with, this may not be noted as a problem, as the glaciers will provide the rivers with more water as the ice disappears. The increase will be dramatic. In Central Asia,
for example, there is an anticipated threefold increase by 2050. However, this can’t last forever and it’s estimated that by 2100, run-off will have reduced to two thirds of present-day volume. Already, dry season water resources are under stress, and demand continues to increase, so any reduction in glacial flow could potentially lead to widespread hardship for those who rely on glacial run-off for their water supply, which could in turn, create geopolitical tension.
In Kazakhstan, for example, there is a looming crisis that has been highlighted by the work of Stephan Harrison from Exeter University. ‘The former capital of Almaty in the southeast has two sources of water for its people, agriculture and industry,’ he says. ‘There is the River Ili, which flows in from China and is potentially going to be much reduced in volume as dams and diversions are erected to meet China’s needs. And then there is the one local source from the glaciated Bolshaya and Malaya Almatinka drainage basins lying 30 kilometres south of Almaty.’
Harrison’s study has drawn on an invaluable historical resource: the Tuyuksu glacier in the Malaya Almatinka valley has been monitored since 1879. ‘It’s clear that they are melting rapidly,’ Harrison says. ‘Between 1955 and 2000, the glaciers have lost around 0.7 per cent of their mass per year. Over this period, the glaciers reduced their total surface area from 272 to 201 square kilometres.’
As the glaciers melt, the residents of Almaty will come to rely more and more on water from the River Ili, undoubtedly leading to tensions with China.
Looming catastrophes
However, there is a more dramatic problem. As glaciers melt, the meltwater is often held back by a mass of moraine, debris left behind by the retreating glacier. This leads to the formation of a glacial lake, and the rapid rate at which many glaciers are now melting is leading some of these lakes to grow extremely quickly. Researchers have found that retreating glaciers can help fill glacial lakes so rapidly that their area can grow by 350 per cent in just 15 years; some glacial lakes in Nepal have grown to almost eight
times the size they were during the 1970s.
The natural dams holding all of this water in are very unstable, and when they break, the so-called glacial lake outburst floods (GLOFs) that result can be devastating, involving the sudden release of hundreds of millions of cubic metres of water.
Between 1977 and 1998, five GLOF events occurred in Nepal. One of the best documented took place on 4 August 1985, when a large chunk of ice broke from the upper section of
the Langmoche glacier in the country’s east and splashed into Dig Tsho glacial lake, causing the lake to break through its 50-metre bank of ice and moraine and releasing ten million cubic metres of water in three hours. The resultant floodwaters rose up to 15 metres in height and the effects were felt more than 90 kilometres downstream. Thirty houses, 14 bridges and US$4million worth of cultivated farmland were destroyed, as was the almost completed US$1.5million Namche Small Hydropower Project.
Of the 3,250 Himalayan glaciers in Nepal, 2,315 contain glacial lakes that are currently increasing in size. For example, Tsho Rolpa in the Rolwaling valley is now six times larger than it was during the 1950s. The lake represents a serious risk to the people, livestock, property and infrastructure of the village of Tribeni, which is located 108 kilometres downstream and has a population of 10,000 people.
Nepal isn’t the only country facing such threats. In Bhutan, there have already been two catastrophic outburst floods. In 1994, a lake burst free in the Lunana area, killing 21 people, washing away bridges and leaving the valley filled with debris and logs. A report produced earlier this year by the International Centre for Integrated Mountain Development identified 20 potentially dangerous glacial lakes in Nepal and 24 in Bhutan.
And it isn’t just the Himalayan glaciers that present such a threat to life. In July 1998, a GLOF in the Shahimardan valley of Kyrgyzstan and Uzbekistan killed more than 100 people. Another in August 2002 in the Shakhdara valley of the Tajik Pamir mountains claimed 23 lives. And in Peru, it has been estimated that 32,000 people were killed by GLOF events during the 20th century. For example, in 1941, a chunk of ice falling into Lake Palcacocha triggered a flood that killed 7,000 people. Recent satellite photos have revealed that another chunk of ice is poised above the lake, potentially threatening the lives of 100,000 people living in the valley below.
Start the slideshow (6 pictures)
Rising tide
However glaciers lose their ice, whether by calving or melting, the water eventually ends up in the ocean. A number of different models have predicted what effect this will have on sea levels. Scientists at the National Snow and Ice Data Centre, based at the University of Colorado, have estimated that if all of the world’s ice fields and glaciers were to melt, global sea levels would rise by 70 metres.
However, such a scenario is unlikely to take place for several centuries. In the meantime, it’s the demise of some of the world’s smaller glaciers that should have us concerned. In a recent paper published in Science, a team led by Mark Meier of the University of Colorado predicted a 24-centimetre rise in sea level by 2100 from small glaciers alone. When this is combined with the gradual thaw of Greenland and Antarctica, Meier estimates that levels will rise by 56 centimetres, just from ice melt.
(This may not sound like much, but you have to take into account the fact that a 30-centimetre rise in sea level will typically lead to a retreat in the shoreline of 30 metres or more. Some 100 million people currently live within the equivalent of about a metre’s rise in sea level.)
The input of all of that cold fresh water is also likely to cause major shifts in ocean and atmosphere circulation, according to Hubbard. The exact nature of those shifts is still the subject of intense debate among geographers.
Special conditions
While the evidence of glacial retreat is overwhelming, and the argument for blaming global warming seemingly watertight, we must still avoid making simplistic assumptions about bigger issues from the misreading of the evidence presented by glaciers.
An important case study is Kilimanjaro. The highest mountain in Africa, near the equator in Tanzania, is famous for the glaciers at its peak. These have been disappearing at an alarming rate; in the past 100 years, 90 per cent of the ice has disappeared, and there have been predictions that the mountain will have completely lost its ice cover by 2020.
Ice core studies on Kilimanjaro have revealed frozen organic matter from 9,000 years ago, suggesting that the glaciers have been in place at least that long. So what has caused the rapid retreat? Environmentalists have leapt on the iconic mountain as symbolic of the fate of glaciers and ice sheets around the globe. But has the ice been melting because of anthropogenic climate change?
Not according to Austrian glaciologist Georg Kaser. He argues that conditions on Kilimanjaro are special, and that the loss of ice is explained by reduced rainfall in the region, creating a drier environment that allows sublimation to take place. Kaser isn’t a climate-change denier, but he believes that Kilimanjaro ‘is not an appropriate poster child for global climate change’.
The example of Kilimanjaro illustrates the complexity of both glacial systems themselves and the way in which they respond to climatic changes. ‘Glacier response isn’t straightforward,’ says Hubbard. ‘It’s complicated by a number of other factors that may dampen or amplify that response. These factors include the configuration and shape of the landscape in which the glacier sits (steep glaciers tend to respond more rapidly but less extensively than low-gradient ones), the mechanics and the dynamics at the base of the glacier – if the ice melting at the surface reaches the glacier bed, it tends to accelerate the glacier flow and hence its response to climate warming.
‘Glaciers also respond to nuances in the seasonal climate,’ he continues. ‘Across Europe, the 1970s tended to be a time of shorter summers, with the onset of ‘winter’ taking place much earlier than it does now and with more precipitation – snow in September, for example. It isn’t well known that more than half of the glaciers in the Swiss Alps were advancing during the 1970s.’
Even today, many of the world’s glaciers are holding their own and, paradoxically, about ten per cent are actually increasing in size.
A March 2005 survey of 50 glaciers in New Zealand by the National Institute of Water and Atmospheric Research (NIWA) found that on average, the glaciers in New Zealand’s Southern Alps had gained considerably more ice than they had lost during the previous year. The gains were due to increased snow in the Southern Alps, particularly from late winter to early summer of the previous year, at which time temperatures were 0.6°C below average, producing more snow. ‘Over the past three years, the glaciers have gained in mass, halting the declines seen between 1998 and 2002,’ said NIWA principal scientist Dr Jim Salinger at the time. ‘This past year was the seventh-largest gain since we started aerial surveys in 1977.’
Similarly, a number of glaciers in Pakistan’s Upper Indus River Basin have been growing. Although meteorological data show that winter temperatures have been rising in parts of the Western Himalaya, Karakoram and Hindu Kush mountain ranges, the region’s winter snowfall has also been on the rise. And the average summer temperatures have been dropping, reducing the rate of melting.
Do these examples provide a glimmer of hope that the doom-mongers might have been wrong? Unfortunately not. In fact, they provide further support to the contention that the planet is in the process of great climatic change. Warming can generate more precipitation and this can fall as snow on glaciers, contributing to their growth.
Mount Shasta, the fifth-highest mountain in California, is a case in point. In 2002, Slawek Tulaczyk and Ian Howat of the University of California, Santa Cruz, undertook the first detailed survey of the mountain’s glaciers in 50 years. To their surprise, they found not retreat, but growth. The tongue of the Whitney Glacier, for example, is moving forward at around ten centimetres per day. In the past 50 years, the glacier has expanded by almost a third, the only glacier in the world known to be larger than it was in 1890, at the height of the Little Ice Age.
The researchers suspect that the growth is actually the result of global warming. Shasta is part of the Cascade Range, which runs down the USA’s west coast. Increases in temperature of the air over the Pacific Ocean has meant that it’s able to carry more moisture, which then falls on Shasta’s glaciers as snow. The annual snowfall that the mountain receives currently exceeds the summer melt by as much as 40 per cent.
And things can change quickly. During the late 1990s, it was reported that numerous glaciers in Norway and Sweden were growing at unprecedented rates. Again, this was down
to changing patterns of precipitation. Not long after, a further rise in air temperature saw the glaciers begin to retreat.
Serious threat
Glaciers are contradictory. They allow people to live when the rains don’t fall, yet they threaten the very lives of the people they nurture. Perhaps they are more important than we imagine – as they offer so distinct and clear an indication of changes in our climate, they might just be charismatic enough to get more people
to take the threat seriously: because if we don’t, these mighty water towers will vanish and we will all feel the consequences.
Two-minute warning
If a 15-metre-high wall of water was hurtling down a river valley towards your village, you would want to know about it. And with such a scenario becoming increasingly likely as glaciers melt and glacial lakes grow, numerous organisations are setting up glacial lake outburst flood (GLOF) early warning systems designed
to detect impending GLOFs in sufficient time to relay a warning to those who might be affected so they can move to safer ground.
Nepal’s Department of Hydrology and Meteorology has installed an early warning system in the villages of the Tama Koshi valley, which are threatened by Tsho Rolpa glacial lake. Six water-level sensors have been installed in the river channel immediately downstream of the lake outlet. Armoured and shielded cables connect the sensors to a transmitter station located about 80 metres away, higher up the slope.
Within two minutes of the initiation of a flood, the system will immediately set off warning stations in the villages, which consist of an air-powered horn backed up by an electric horn. The entire warning system is fully automated, redundant and requires no human intervention.
December 2007
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