Climate Change Impact on Sea Ice Decline. In the Arctic, temperature has increased at twice the rate as the rest of the globe, and could increase by another 8. The warming atmosphere along with new weather pattern extremes is causing Arctic sea ice to melt at an alarming rate—1. Arctic will be ice- free by 2. The impacts of dwindling ice cover in the Arctic are far- reaching, from species endangerment to enhanced global warming, to the weakening or shut- down of global ocean circulation. In today's climate regime, sea ice has been observed as far south as Bohai Bay in China—a latitude comparable to the Mediterranean Sea. Sea ice begins to form when water temperature dips just below freezing, at around - 1. It grows into small sheets that look like pancakes, and eventually merge together to form large ice floes which can span miles. As the ice forms, it expels the salt, which increases the density of the surrounding water and thus plays a critical role in global ocean circulation. Figure 1. Bright white sea ice reflects almost all of the incoming solar radiation back to space, whereas the dark ocean surface absorbs nearly all of it. Image source: Stephen Hudson / Norsk Polarinstitutt. Winter temperature has increased more than summer temperature, which is a trend that is expected to continue. While some have suggested that these variations in temperature and associated sea ice melt are a natural cycle, recent research tells us that the Arctic was in a 2,0. Sea ice is generally moderated by sunlight—it grows in the winter and melts in the summer—but there are other factors at play in the decline of ice in the Arctic Ocean. Warm ocean currents travel north from the equator and usher in warmer and warmer water, making sea ice growth difficult. Weather patterns over the high mid- latitudes and the Arctic can also affect sea ice growth. Under normal climate conditions, cold air is confined to the Arctic by the polar vortex winds, which circle counter- clockwise around the North Pole. As sea ice coverage decreases, the Arctic warms, high pressure builds, and the polar vortex weakens, sending cold air is spilling southward into the mid- latitudes, bringing record cold and fierce snowstorms. As soon as the ice falls into the ocean, the ocean rises a little. If the rising temperature affects glaciers and icebergs, could the polar ice caps be in danger of melting and causing the oceans to rise? Discovering the Ice Age As early as 1787, Bernard Kuhn believed that erratic boulders in Swiss Jura were the result of ancient glaciation. Although climate scientists have worked hard to determine the ultimate trigger of abrupt climate change during the last ice age, it is likely that a combination of ocean and atmospheric circulation changes were involved. At the same time, warm air will flowing into the Arctic to replace the cold air spilling south, which drives more sea ice loss. This reversal could be partially driven by sea ice loss, and so is expected to surface more often in the coming years. The primary role that sea ice plays in global climate its ability to efficiently reflect the Sun's radiation. This property is called . The albedo of snow- covered sea ice is 0. Sun's radiation. Just like wearing a white shirt will keep you cool when you're out in the Sun, the sea ice covering the Arctic keeps the thermostat low. The ocean surface, however, is almost black, and it only reflects 1. After something absorbs sunlight, it emits heat. Less sea ice and more ocean surface will lead to a warmer Arctic, and a warmer climate. Observed Sea Ice Melt. Modeling Thermodynamic Ice–Ocean Interactions at the Base of an Ice Shelf DAVID M. HOLLAND Lamont-Doherty Earth Observatory, Palisades, New York ADRIAN JENKINS British Antarctic Survey, Cambridge, United Kingdom (Manuscript received 6 May. Oceanographers and ice experts have begun a five-year field campaign to study how the ocean might be melting Greenland’s icy edges. At 1.7 million square kilometers (660,000 square miles), the Greenland ice sheet is three times the size of Texas. Loss of sea ice contributes to global warming by exposing dark open surfaces of water that then absorbs the sun's energy and in turn leads to additional warming. Global Warming Causes. Satellite data show that since the late 1. September Arctic sea ice extent has decreased by about 1. What's especially alarming is the decrease in multi- year ice. Sea ice is classified by age, usually as . While new ice is very shallow, multi- year ice can grow to be quite thick, typically between 6 and 1. A remarkable study was published in 2. Arctic. In 1. 98. When they surveyed the Arctic again in 2. Likewise, sea ice thickness and volume have decreased markedly since the beginning of the satellite era. Figure 2. September Arctic sea ice extent. Sea ice extent measurements are made with satellite instruments, and are given in millions of square kilometers. Sea ice measurements are available within the satellite era, and are shown here from 1. Data source: National Snow and Ice Data Center. Recent years have set a number of sea ice records in the Arctic. The summer of 2. 00. Unusually strong high pressure over the Arctic led to clear skies and plenty of sunshine. The polar vortex weakened, injecting large amounts of warm air into the Arctic. Sea ice loss doubled to 3. National Snow and Ice Data Center. In one year, as much ice was lost as in the previous 2. In 2. 01. 1, the University of Bremen reported that sea ice had reached a new all- time low on September 8th, and was 2. Extraordinary melting of sea ice in the Arctic in 2. September 2. 00. 7. The new sea ice record was set on August 2. National Snow and Ice Data Center. A comprehensive collection of sea ice graphs shows the full story. Satellite records of sea ice extent date back to 1. Kinnard et al. The Northeast Passage is a shipping route that runs along the northern Russian coast and to the Bering Strait, and is sometimes called the . These passages have been elusive since the early 1. The Northeast Passage opened for the first time in recorded history in 2. Northwest Passage in 2. For four years in a row, the Northwest Passage was open for ice- free sailing. It now appears that the opening of one or both of these northern passages is the new norm, and business interests are taking note—commercial shipping in the Arctic is on the increase, and there is increasing interest in oil drilling. The great polar explorers of past centuries would be astounded at how the Arctic has changed in the 2. When was the last time the Arctic was this ice- free? It is very unlikely the Northwest Passage was open between 1. Ships periodically attempted the Passage and were foiled during this period. Research by Kinnard et al. We may have to go back to at least 4,0. B. C. Funder and Kjaer (2. North Greenland coast, which suggested the Arctic Ocean was ice- free in the summer for over 1,0. Earth's orbital variations brought more sunlight to the Arctic in summer than at present. Prior to that, the next likely time was during the last inter- glacial period, 1. Arctic temperatures then were 2 - 3 . A July 2. 01. 2 study by Day et al. The AMO has two phases, negative (cold) and positive (warm), which impact Arctic sea ice. The negative phase tends to create sea surface temperatures in the far north Atlantic that are colder than average. In this study, the AMO only accounted for 5% - 3. September sea ice decline since 1. The scientists concluded that given the lack of evidence that natural forces were controlling sea ice fluctuations, the majority of sea ice decline we've seen during the 1. The Forecast. Figure 3. Sea ice extent observations (1. NOAA GFDL model. Yearly extent represents an average 8. Click on the image for a larger view. Scientists use numerical models to predict how fast Arctic sea ice is expected to melt in coming decades. Until recently, these climate models have done a poor job predicting the recent record loss of Arctic sea ice. None of the models used in the 2. Intergovernmental Panel on Climate Change (IPCC) report have foreseen the recent, remarkable sea ice loss. This is likely because the models have a hard time understanding the transport of heat within the ocean itself, which some argue causes over 5. Arctic sea ice loss. The NOAA GFDL model paints a similar picture as that of the IPCC models: an ice- free Arctic summer by 2. However, these forecasts are too conservative, and it's looking more and more like the Arctic will be ice- free in the next few decades. Does 2. 01. 2 mark a fundamental change in Arctic ice loss? The previous record low extent in 2. This year, though we did see two strong storms in the Arctic, they weren't like what we saw in 2. It's arguable that 2. Arctic than the minimum we saw in 2. Mark Serreze, the Director the National Snow and Ice Data Center, said about this year's sea ice minimum, . The ice is so thin and weak now, it doesn't matter how the winds blow. However, sea ice minimum has been declining sharply over the past 3. IPCC report. Annual minimum sea ice extent is decreasing at a rate of 1. Forecasts of an ice- free Arctic range from 2. Peter Wadhams of Cambridge University predicted that the Arctic will be ice- free within four years. A recent study by Stroeve et al. These updated models suggest that . The polar ice caps help to regulate global temperature by reflecting sunlight back into space. White snow and ice at the poles reflects sunlight, but dark ocean absorbs it. Replacing bright sea ice with dark ocean is a recipe for more and faster global warming. The Autumn air temperature over the Arctic has increased by 4 - 6. Another non- trivial impact of the absence of sea ice is increased melting in Greenland. We already saw an unprecedented melting event in Greenland this year, and as warming continues, the likelihood of these events increase. The impacts of an ice- free Arctic are far- reaching, and could be a trigger for abrupt, cataclysmic climate change in the future. Although it is difficult to see exactly how sea ice decline will impact the local and global environment, basic understanding of the Arctic as well as recent observations give us a good idea of how things might change. Sea level rise. Direct effect: The melting of the Arctic sea ice will not change ocean sea levels appreciably, since the ice is already floating in the ocean. Sea ice melting does slightly contribute to sea level rise since the fresh melt water is less dense than the salty ocean water it displaces. Robert Grumbine of NOAA's sea ice group, if all the world's sea ice melted, it would contribute to about 4 millimeters of global sea level rise. This is a tiny figure compared to the 2. Greenland Ice Sheet, which is on land. Indirect effect: The biggest concern regarding Arctic sea ice loss is the warmer average temperatures it will bring to the Arctic in coming years. Warmer temperatures will accelerate the melting of the Greenland ice sheet, which holds enough water to raise sea level 2. Although the IPCC's 2. Greenland ice sheet and other factors, these estimates will probably need to be revised upwards in light of the unexpectedly high sea ice loss in the Arctic. Weather patterns. NOVA - Official Website . Maasch. Posted 0. NOVA. During the past billion years, the Earth's climate has fluctuated between warm periods—sometimes even completely ice- free—and cold periods, when glaciers scour the continents. In this article, climate scientist Kirk Maasch offers perspective on these historic changes, including the likely causes of the last great ice age—which contrary to common knowledge, we are still in the midst of. To understand changing climate today, we need a perspective on changes of the past. During an ice age, the polar regions are cold, there are large differences in temperature from the equator to the pole, and large, continental- size glaciers can cover enormous regions of the Earth. For the Cenozoic period, which began about 7. This record indicates decreasing deep- water temperature, along with the build- up of continental ice sheets. Much of this deep- water cooling occurred in three major steps about 3. Our climate today is actually a warm interval between these many periods of glaciation. The most recent period of glaciation, which many people think of as the . Tropical conditions actually extended all the way into the mid- latitudes (around northern Spain or the central United States for example), polar regions experienced temperate climates, and the difference in temperature between the equator and pole was much smaller than it is today. Indeed it was so warm that trees grew in both the Arctic and Antarctic, and alligators lived in Ellesmere Island at 7. North. Between 5. East Antarctica, reaching down to sea level in some places. Close to Antarctica, the temperature of the water near the surface dropped to between 5 and 8 degrees Celsius. Between 3. 6 and 2. Earth experienced the first of three major cooling steps. At this time a continental- scale temperate ice sheet emerged in East Antarctica. Meanwhile, in North America, the mean annual air temperature dropped by approximately 1. Celsius. The Earth was once more released from the grip of the big chill between 5 and 3 million years ago, when the sea was much warmer around North America and the Antarctic than it is today. Warm- weather plants grew in Northern Europe where today they cannot survive, and trees grew in Iceland, Greenland, and Canada as far north as 8. North. Around 2 and a half million years ago, tundra- like conditions took over north- central Europe. Soon thereafter, the once- humid environment of Central China was replaced by harsh continental steppe. And in sub- Saharan Africa, arid and open grasslands expanded, replacing more wooded, wetter environments. Many paleontologists believe that this environmental change is linked to the evolution of humankind. Plate motions lead to cycles of ocean basin growth and destruction, known as Wilson cycles, involving continental rifting, seafloor- spreading, subduction, and collision. Several explanations of the latest cooling trend that involve a climate- tectonic connection are summarized below. The re- distribution and changing size and elevation of continental land masses may have caused climate change on long time scales. Computer climate models have shown that the climate is very sensitive to changing geography. It is unlikely, however, that these large variations in the Earth's geography were the primary cause of the latest long- term cooling trend as they fail to decrease temperatures on a global scale. Computer model experiments performed to test the climate's sensitivity to mountains and high plateaus show that plateau uplift in Tibet and western North America has a small effect on global temperature but cannot explain the magnitude of the cooling trend. Plateau uplift does, however, have a significant impact on climate, including the diversion of North Hemisphere westerly winds and intensification of monsoonal circulation. This theory suggests that the redistribution of heat on the planet by changing ocean circulation can isolate polar regions, cause the growth of ice sheets and sea ice, and increase temperature differences between the equator and the poles. But atmospheric climate modeling experiments show that even if the ocean did transport enough heat up to the coast of Antarctica to maintain sea surface temperatures at 1. Celsius, the interior conditions would still be much colder—and this is contrary to the geologic record. It is possible, however, that changes in heat transport caused by variations in ocean gateways may have played a significant role in cooling trends over the last 6. Carbon dioxide influences the mean global temperature through the greenhouse effect. The globally averaged surface temperature for the Earth is approximately 1. Celsius, and this is due largely to the greenhouse effect. Solar radiation entering earth's atmosphere is predominantly short wave, while heat radiated from the Earth's surface is long wave. Water vapor, carbon dioxide, methane, and other trace gases in the Earth's atmosphere absorb this long wave radiation. Because the Earth does not allow this long wave radiation to leave, the solar energy is trapped and the net effect is to warm the Earth. If not for the presence of an atmosphere, the surface temperature on earth would be well below the freezing point of water. Degassing reactions associated with volcanic activity and the combining of organic carbon with oxygen release carbon dioxide into the atmosphere. Conversely, the burial of organic matter removes carbon dioxide from the atmosphere. It has been suggested that the Eocene, the early warm trend 5. One mechanism proposed as a cause of this decrease in carbon dioxide is that mountain uplift lead to enhanced weathering of silicate rocks, and thus removal of carbon dioxide from the atmosphere. While topography may not be enough to explain the cooling trends, another mechanism may account for changing climate. The uplift may have caused both an increase in the global rate of chemical erosion, as well as erode fresh minerals that are rapidly transported to lower elevations, which are warmer and moister and allow chemical weathering to happen more efficiently. Through these mechanisms, then, it has been hypothesized that the tectonically driven uplift of the Tibetan Plateau and the Himalayas is the prime cause of the post- Eocene cooling trend. This feature originally appeared on the site for the NOVA program Cracking the Ice Age. Kirk A. Maasch is a professor at the University of Maine, in the Department of Geological Sciences.
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