Global warming is causing rapid and dramatic changes to ecological systems worldwide, but the changes that are being experienced due to the global meltdown of the cryosphere are the most dramatic, and may prove to have the most drastic consequences to all life on Earth as these worlds transform.
Rising atmospheric temperatures, due to heat being trapped within the atmosphere by greenhouse gases, such as carbon dioxide, nitrogen, and methane, are not only melting polar ice sheets and sea ice, but are also causing ice floes and glaciers in polar and temperate regions to meltdown. These glaciers serve important ecological functions to both the surrounding ecosystems, and to the world as a whole.
The Life Cycle of a Glacier
Glaciers are formed when snow that accumulates on land is greater than the rate of summer melting. As the snow accumulates, the weight of the accrued snow pushes down on the layers below, compacting these layers into ice. When layers of compacted ice accumulate on an incline, it will eventually start to move down the slope due to the force of its own weight and gravity, giving birth to a glacier that over time carves a deep channel into the landscape as it grinds along. During the warm summer months, when melting is highest, water may drain to the base of the glacier and act as a lubricant, which can accelerate the rate of ice flow down the slope. In winter more snow is added to the source, which over time accumulates and compresses to replenish the ice that has moved downhill. Ice is lost from a glacier by calving, where large chunks of ice at the front of the glacier shear off into tidewater to form icebergs; or by melting. When ice is removed faster than it is replenished, the glacier starts to recede.
Glaciers around the world from the Antarctic to the Arctic, including those in South America, North America, Canada, Greenland, Europe, China, New Zealand, and Africa, are rapidly melting, and are retreating at an alarming rate. The rapid loss of these glaciers has serious implications to ecosystems, and to human populations who are sustained by them. Some of the potential consequences of melting glaciers include: flooding, mudslides, and rock falls; which can jeopardize human safety, and affect tourism, trade, industry, and economic development.
Glaciers cover approximately 10 percent of the world’s land surface; they play an important role in the global water cycle, and determine the volume and variability of water runoff, plus the quality of water they supply to surrounding areas.
According to research conducted by McGill doctoral student, Michel Baraer, on Peru’s Cordillera Blanca glacier, glaciers are retreating by approximately 1% per year, and this is increasing steadily. This rate of shrinkage is much higher than initially predicted. Yet, while the glacier is steadily melting, the volume of water draining into the Rio Santa in Northern Peru from the glacier has dropped off significantly. Baraer and his fellow researchers, Prof. Jeffrey McKenzie from McGill, and Prof. Bryan Mark from Ohio State University, estimate that water levels can be reduced by as much as 30% lower than their current levels. Baraer explains that “when a glacier starts to retreat, at some point you reach a plateau and from this point onwards, you have a decrease in the discharge of melt water from the glacier. Where scientists once believed that they had 10 to 20 years to adapt to reduced runoff, that time is now up.” Almost all the watersheds that they studied provided good evidence that discharge of peak water has been passed, and is now in decline. The prospect of a severely reduced water supply could be serious for the millions of inhabitants in the region who are dependent upon this water source for drinking water, hydropower, or to irrigate their crops. It also has huge implications for ecosystems downstream that depend on the water flow to keep them functioning effectively, and ultimately, on the wildlife and people who depend on these habitats.
This is only the tip of the iceberg, so to speak. Reports of retreating glaciers around the world show a similar trend. The World Wildlife Fund (WWF) is concerned that rapidly melting glaciers will initially lead to widespread flooding, but their greater concern is that the longterm outcome will be reduced water supply draining from the glaciers.
While Greenland and Antarctica hold the largest ice reserves, the smaller glaciers dotted around the world are significant in terms of the role that they play as freshwater reservoirs. According to the WWF, glaciers contain 70% of the world’s freshwater supply, and provide a buffer against climate variability by releasing water during the dry season. The WWF has been concerned about the effects of shrinking glaciers for some time, pinpointing the regions most at risk from melting glaciers due to climate change as: Ecuador, Peru, and Bolivia, where glaciers supply water throughout the year, and in many cases are the only source of drinking water supplying major cities during dry periods; the Himalayas, where a third of the world’s population is dependent on water supplied by glacier-fed rivers, and the threat of catastrophic flooding is a real concern; and small island nations such as Tuvalu, where drinking water reservoirs and groundwater aquifers are being contaminated with saltwater as sea levels rise and submerge low-lying areas.
But humans are not the only species that face problems in the future due to melting glaciers. Many species will be threatened by habitat loss as their worlds transform. Animals that live on ice are threatened as their icy habitat shrinks, while those that live in coastal habitats are threatened by rising sea levels that will engulf low-lying regions. Wildlife cited as being at risk of extinction by the WWF include: the Royal Bengal tiger, which is threatened by habitat loss due to rising sea levels; the Kittlitz’s murrelet, a bird that lives and breeds exclusively on glaciers, is threatened as these unique habitats disappear; and even tropical coral reefs, far removed from glaciers, will be affected as sea levels rise, reducing the ability of sunlight to penetrate to the deeper waters, which will thus limit the ability of coral to sustain themselves through photosynthesis.
Rising Sea Levels
While there has been much focus on the melting of large polar ice sheets and sea ice, in terms of their contribution to rising sea levels, the contribution of meltwater from smaller glaciers to sea level increases has been given much less attention. Several recent studies show that glaciers are important contributors to rising sea levels. In a paper recently published in Nature Geoscience, Valentina Radić from the University of British Columbia, used complex models to predict the future rate of glacier melt, and the contribution of this meltwater to global sea level increases. These projections indicate that glaciers will be reduced by approximately 21% by 2100, while the most important contributors to global sea level increases will be reduced by more than 50%, with some glaciers losing up to 75% of their total ice volume. These modeled projections, which exclude glacial calving to form icebergs at the glacier/tidal interface, and the contribution from melting polar ice sheets and sea ice, show that glaciers are expected to contribute 12 centimeters (4.7 inches) to sea level increases by the end of this century.
According to another study, published in Science by Professor Mark Meier and fellow researchers from the University of Colorado at Boulder, in 2007 glaciers were contributing 60% of the world’s ice to the oceans, with Greenland contributing about 28%, and Antarctica 12%. This rate has been accelerating over the last decade. ”The contribution is presently about 100 cubic miles of ice annually – a volume nearly equal to the water in Lake Erie – and is rising by about three cubic miles per year,” states Meier. The study attributes the speeding up of the rate at which glaciers and ice caps are contributing to rising sea levels, to rapid changes in the flow of tidewater glaciers that discharge icebergs directly into the ocean. According to co-author, Professor Robert Anderson, ”Many tidewater glaciers are undergoing rapid thinning, stretching and retreat, which causes them to speed up and deliver increased amounts of ice into the world’s oceans. Water controls how rapidly glaciers slide along their beds. When a glacier with its ‘toe in the water’ thins, a larger fraction of its weight is supported by water and it slides faster and calves more ice into the ocean at the glacier terminus.”
The researchers estimated that the accelerating rate of melt from glaciers and ice caps could contribute between 4 to 9.5 inches (approximately 10 to 24 centimeters) to global sea level rise by 2100. This estimate is higher than that projected by the previous study undertaken by Radić, as it includes ice lost from glaciers by calving. However, it does not take into account the fact that warming ocean water expands, which could potentially double the estimated figures. This could have severe implications to coastal communities, considering that 100 million people live within three feet of the current high water mark, and an increase in sea level by one foot can cause the shoreline to retreat by 100 feet or more, as the high water mark advances.
Persistent organic pollutants (POPs), such as PCBs and DDT, used as chemical pesticides in the mid-1900′s, persist in the environment, and accumulate up the food chain, becoming more concentrated in animals higher up the food chain – including man, often with grave health consequences. As a result, these chemicals have since been banned in most countries across the world, except Africa, where DDT is still used to combat malaria, which poses an even greater threat to human health. During their use these chemical pesticides were carried by wind, and deposited on ice sheets and glaciers, where they have remained trapped within the ice. However, the recent meltdown of glaciers and ice sheets has facilitated the release of these pollutants back into the environment, where they can once again affect the health of both wildlife and humans that are exposed to them. In addition, toxic heavy metals, such as mercury, are still circulating to the Arctic from the industrialized nations, and accumulating in species at levels that can pose a health risk.
According to research undertaken by Professor Bjorn Munro Jenssen, an eco-toxicologist from the Norwegian University of Science and Technology (NTNU), many of the pollutants that are stored in the ice are endocrine-disrupting chemicals (EDCs), which affect the endocrine system, particularly the thyroid hormones, sex steroid hormones, and glucocorticosteroids. These hormonal imbalances can compromise the immune system; effect metabolic processes, including growth and development; and can impair cognitive and learning capacity, which is vital for hunting and survival in a harsh and rapidly changing environment. In addition, disruption of the sex hormones can cause changes in sexual behavior, infertility, and birth defects, resulting in reduced reproductive success. Jenssen is concerned that these factors may ultimately compromise an animal’s ability to adapt to climate change. ”Climate change and exposure to endocrine-disrupting chemicals (EDCs) are currently regarded as two of the most serious anthropogenic threats to biodiversity and ecosystems. We should, therefore, be especially concerned about the possible effects of EDCs on the ability of Arctic marine mammals and seabirds to adapt to environmental alterations caused by climate change”, says Jenssen. ”Because different endocrine systems are important for enabling animals to respond adequately to environmental stress, EDCs may interfere with adaptations to increased stress situations.”
As these pollutants are stored in the organs and body fat of animals, they become more concentrated up the food chain. Consequently, top predators are most at risk from the effects of the contaminants. As the ice melts, the pollutants are released into the surrounding seawater, where they enter filter feeding organisms at the bottom of the food chain, such as plankton and fish. When predators, such as seabirds or seals, feed on fish that have the pollutants stored in their body tissue, these are then absorbed into the body tissue of the predator. While consuming one or two contaminated prey items is not likely to cause any significant harm, the effects of long-term exposure may be far more damaging to predators. Polar bears are particularly at risk, as they are not only apex predators in the arctic food chain, but they also consume large quantities of seals, eating only the fat, which is where the contaminants are stored. Considering that an adult polar bear can eat a few hundred seals a year, it is quite easy to see how the cumulative affect of these pollutants can be detrimental to the health and wellbeing of the bears.
The problem is not limited to seals and polar bears; even people are at risk, particularly indigenous populations, who are effectively top predators that depend on many of these animals for their survival. According to a statement delivered by the Arctic Indigenous Delegation to the Fourth Conference of Parties in Geneva, May 2009, ”Arctic Indigenous Peoples suffer levels of persistent organic pollutants contamination in blood and breast milk that are among the highest of any population on earth, even though these chemicals have never been produced in the Arctic.” This is the real tragedy – people and animals who live in remote and seemingly pristine corners of the world, who are the least responsible for the current mess the planet is in, are the most vulnerable, and the most at risk of extinction.
As glaciers and ice sheets continue to melt in the future, there will be an increase in widespread flooding; the resultant sea level rise will threaten coastal communities and coastal habitats; and millions of people will face water shortages as glaciers steadily recede. All living organisms need water to survive; it is our most precious resource, yet it is often taken for granted. Glaciers act as a storage facility for 70% of the Earth’s freshwater reserves, and if these freshwater reservoirs systematically dry up, it could spell disaster for many ecosystems and organisms that depend on them for survival, including man. The resurfacing of chemicals and heavy metal pollutants that have been out of circulation for many years should be a strong warning that the sins of our past will come back to haunt us. If we do not make a concerted effort to reduce industrial pollution, and slow down the rate of global warming, we may be in for more nasty surprises in the future.
Bjorn Munro Jenssen. ‘Endocrine-Disrupting Chemicals and Climate Change: A Worst-Case
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McGill University. ‘Retreating glaciers threaten water supplies.’ 20 Dec. 2011. Web. 30 Dec. 2011. http://www.eurekalert.org/pub_releases/2011-12/mu-gti121511.php
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