Glacier melts around the world are an area of concern, especially with regard to loss of precious freshwater reserves. However, melting of ice sheets is most dramatic in the polar regions, where ice sheets and glaciers are diminishing at an alarming rate in both the Arctic and Antarctic regions. This has serious implications – not only for these ecosystems, and the wildlife that live there – but also for the rest of the planet, and all its inhabitants. Furthermore, the melting of ice sheets produces a number of feedbacks that increases the rate of global warming exponentially.
Threats to Wildlife
The polar regions provide a habitat for a range of wildlife that are uniquely adapted to life in these harsh environments. The rapid change in both temperatures and habitat is too fast to allow them to adapt, and is catching them unawares.
Threatened Wildlife: Arctic
In the northern Arctic regions polar bears face risk of extinction as diminishing ice sheets become situated further apart, forcing them to swim longer distances when crossing between ice sheets in search of food. Polar bears have been seen swimming in large groups in open water 60 miles from the shore. The larger expanse of water makes conditions rough due to increased wave action, and the extra distance tires them out. As a result, many have drowned. Polar bears hunt on the ice, and do not eat when they are land bound. As the ice sheets are melting earlier, and the distance between ice sheets is becoming further apart, many polar bears are forced to spend longer periods on land, and consequently lose condition.
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A recent long-term study on polar bears in Hudson Bay, Canada, shows that this population is losing weight and giving birth to fewer cubs. Polar bears fast for eight months on land in summer, where they give birth to their young in the warmth and protection of an underground den. During this time an adult polar bear can lose up to 400 pounds – more than half its body weight. Come winter, the mother polar bear must venture out onto the ice to hunt seal pups in a race against time, in order to gain weight and fat reserves to carry her through the long summer land-bound phase. A polar bear’s staple diet consists largely of seals, which they hunt on the ice. Once the ice starts melting at the beginning of summer, the seals swim off into open water, and are no longer readily available as a food source for polar bears. It is critical that the female packs on the pounds during this small window period. If she loses too much weight she will stop producing milk, and will not be able to successfully raise her cubs. Adults in poor condition produce cubs that fail to thrive, and thin, lightweight cubs are less likely to survive into adulthood. This study shows that the reproduction success of polar bears is being affected by earlier melting of the ice sheets in Hudson Bay, leading to adult polar bears being in a poor condition, and consequently producing fewer cubs. The long-term outlook is a dwindling polar bear population.
Threatened Wildlife: Antarctic
In Antarctica, breeding penguins have also been effected by warming temperatures and melting ice. In 2001 a huge iceberg, the B-15, sheared off from the Ross Ice Shelf, drifted down the coastline, and crashed into the coast at Cape Crozier, alongside two major breeding colonies of Emperor penguins. The force of the impact caused large blocks of shattered ice to smash into one colony, crushing and killing many incubating penguins. The iceberg affected wind and current patterns, which allowed ice to build up. The accumulated ice, together with the huge iceberg, blocked off the penguins’ easy access route to the sea from the breeding colony. This forced them to walk or swim an extensive distance around the iceberg to reach feeding grounds, and then return by the same extra long detour back to the colony. This resulted in complete nest failure of the affected colonies, as adult penguins were forced to abandon their nests. Four years later, with portions of the iceberg still blocking their direct access to the sea, the penguins breeding success was still reduced to between 0 to 40% of the chicks produced in 2000 – before the iceberg collided with their colony, and changed the dynamics of their breeding habitat. Penguins are already threatened by food shortages due to overfishing, which is exacerbated as global warming makes the oceans less productive, and fish and krill – on which they feed and raise their chicks – becomes more scarce.
The melting of ice sheets is not only an effect of global warming, but it also provides positive feedback into the cycle to further escalate global warming. The concern is that multiple feedback loops will drive runaway global warming, escalating it to a point where it will be impossible to stop, or even slow down. This is most significant in the Arctic region, which is warming faster than any other region on Earth. There are a number of reasons for this.
First, the ice sheets reflect heat away from the Earth and help keep it cool – this is known as the albedo effect. As ice changes from a solid phase to a liquid, instead of reflecting heat away from the Earth, the heat is absorbed by the darker water. World renowned climate scientist, James Hanson, refers to this as the ‘albedo flip’ property of ice/water, which provides a powerful local feedback that can act as a trigger mechanism to increase both melt intensity, and the duration of the melt season. According to Hanson, ”A climate forcing that ‘flips’ the albedo of a sufficient portion of an ice sheet can spark a cataclysm. Inertia of ice sheet and ocean provides only moderate delay to ice sheet disintegration and a burst of added global warming. Recent greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of our control, with great dangers for humans and other creatures.”
Release of Methane
Another source of positive feedbacks to global warming are carbon reserves that are stored predominantly in the form of methane in frozen substrates. Methane is stored as methane hydrate trapped in frozen underwater sediments at the bottom of the ocean, and in the soils under permafrost. This methane is released into the atmosphere as these icy layers melt. As methane is an extremely potent greenhouse gas, the release of these trapped reserves compounds the effects of global warming.
As ocean temperatures steadily rise, the warm water being fed into the Arctic from the Atlantic Ocean is 2º C warmer than it has been in over 2000 years, as a result of Arctic warming. This is yet another feedback loop that further increases the rate at which the ice sheets diminish. Not only are the ice sheets surrounded by warmer air, but warmer water too. Cold water is essential for the formation of sea ice – without it, sea ice cannot form in winter. Moreover, this warmer water has the potential to further increase the rate of melting.
According to a recent study conducted by Jianjun Yin, an assistant professor of geosciences at the University of Arizona, the subsurface ocean layers surrounding the polar ice sheets will warm substantially as global warming progresses. Using complex models, he predicts that the subsurface waters surrounding the Greenland coast could increase by 3.6° F (2° C) by 2100. This has significant implications for ice sheets and sea level increase. ”Ocean warming is very important compared to atmospheric warming because water has a much larger heat capacity than air,” Yin explains. ”If you put an ice cube in a warm room, it will melt in several hours. But if you put an ice cube in a cup of warm water, it will disappear in just minutes.”
Yin’s models estimate an average increase of subsurface sea temperature at depths of 650 to 1,650 feet (200 to 500 meters) of approximately 1.8° F (1° C) by 2100. However, subsurface water is expected to increase by twice as much along the Greenland coast – 3.6° F (2° C), and only half as much along Antarctica – 0.9° F (0.5° C). The difference in the rate of warming between the North and South is attributed to the effect of currents. Warmer subtropical water is carried northwards by the Gulf Stream, while the Antarctic Circumpolar Current inhibits the subtropical warmth from entering the Antarctic’s coastal waters.
Yin predicts that warming of the oceans subsurface layers surrounding ice sheets will melt underwater portions of ice much faster than scientists originally anticipated. Furthermore, much of the ice is made up of tidewater glaciers, where a large portion of the glacier’s leading edge is submerged underwater in a deep fjord. As warm sea water melts the submerged part of the glaciers, they will no longer be able to support the top of the glacier that is visible above water. This will cause the glaciers to collapse into the sea, to form icebergs. As the glaciers melt, the meltwater will lubricate the base of the glaciers, speeding up their seaward movement.
Effect on Oceans
Sea levels rise and fall in response to shifts in global temperatures. More snow and ice accumulates on land during periods of low global surface temperatures, causing sea levels to drop. When global temperatures increase, this causes the snow and ice that has accumulated on land as glaciers and ice sheets to melt, resulting in rising sea levels. Wildlife living on ice sheets, and in coastal regions, are threatened with extinction as these habitats transform to a watery world. The rising sea levels are also a threat to coastal communities, especially island nations, who are less able to move inland as sea levels gradually rise. But there is another less obvious threat that could affect the whole planet.
The global ocean circulation system, commonly referred to as the ‘Ocean Conveyor’, circulates heat around the world. One of the currents that makes up the Ocean Conveyor is the Gulf Stream. Water is warmed by the sun in the tropical equatorial regions, which increases the rate of evaporation, leaving the warm surface waters saltier in the tropics. This warm, salty subtropical surface water is transported northwards up the East Coast of the United States by the Gulf Stream, and is then carried in a northwesterly direction out toward Europe by the North Atlantic Drift. These currents play a vital role in transferring heat and moisture, and thus regulating the climate and weather of North America and Europe. The warm surface water carried in the Gulf Stream cools as it reaches the northern latitudes, releasing heat to the atmosphere. As cold water is denser than warm water, the cooled water sinks to the depths of the ocean, and flows back towards the equator as a deep cold water oceanic current, to replace the warm water transported northwards in the Gulf Stream. When it reaches the tropics it is warmed once again, and the cycle is repeated.
There are primarily two things that drive ocean circulation: temperature and salinity. As ice sheets, ice shelves, glaciers and sea ice continue to melt at an alarming rate, they add vast quantities of fresh water to the ocean. As they melt, the surface area of ice is decreased, and the surface area of the ocean is increased, allowing more moisture to be evaporated from the surface of the ocean. As the moisture in the atmosphere increases, so too does rainfall; which adds yet more freshwater to the oceans surrounding the ice sheets. Scientists are concerned that the addition of all this surplus freshwater is steadily decreasing salinity levels, and is causing the seawater to become less dense. This has significant implications to oceanic currents and ocean circulation,as it could reduce the rate of sinking – the mechanism that is chiefly responsible for driving the downward motion of the water, and circulation of cold deep water back to the equatorial regions. As warm water is less dense than cold water, rising North Atlantic sea temperatures could also affect the density of North Atlantic water, further impacting downward flow. Scientists fear that the reduction in the rate of sinking and deep water flow could initially slow the Gulf Stream, and over time it could halt – or even change direction – with serious implications to global climate and weather.
A recently published study conducted by Uwe Send, of the Scripps Institute for Oceanography, shows observational evidence that the North Atlantic currents have weakened by 20% over a ten year period (2000-2009). Is this just a natural fluctuation, or is it something we need to be concerned about? The disruption of the Ocean Conveyor is believed to have triggered sudden climate change and ice-ages in the past, so maybe we should sit up and take note.
The effects of global warming are approaching the stage where they may run out of our control. Unless we can pull together and slow down the effects of global warming by reducing greenhouse gas emissions – which are largely contributing to global warming, and driving climate change – our world faces risk of runaway global warming that could potentially lead to unprecedented changes to both climate, and land features, in a very short time-frame. While many species are able to adapt to environmental changes over time, when changes occur too rapidly, a large number are not able to adapt to these sudden changes, with vulnerable species that are already threatened being most at risk of extinction. The same is true for vulnerable human populations, mostly from poor nations, who do not have the capacity to minimize risk associated with drastic environmental and climate changes.
An ecosystem is made up of complex interactions between living and non-living components of that system. Every living and non-living component has as essential role to play in maintaining the balance and healthy functioning of that ecosystem. If any component is altered, tampered with, or removed, it can upset the delicate balance, and cause the system to malfunction. It’s time that we start looking at the Earth holistically as one giant ecosystem. Essentially, it functions along the same principals as the teeny weeniest microhabitat – upset any of the components that are essential for the healthy functioning of the system, and it will surely malfunction. Global warming has the capacity to alter and remove vital components of the giant ecosystem that we call Earth, and in so doing, could cause the system to malfunction horribly, and drastically change the face of the planet as we know it.
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