MELTING ICE AND SEA LEVEL
3) ICE MELTS, SEA LEVELS RISE
Currently, polar ice is melting and sea levels are rising. Since the 1978, the amount of arctic ice has undergone an overall reduction of 2.7% per decade and a reduction of summer ice by 7.4% per decade (IPCC, Document I, 2007). In the past 25 years, the amount of annual ice over the Arctic ocean has decreased by 3% per decade and the amount of summer ice over the arctic is 20% less than what it was thirty years ago (IPCC, 2007; Union of Concerned Scientists, 2007; Laidre, 2005). The major ice sheet covering the arctic cracked in half in 2004, something that had never been witnessed before (Gore, 2006). Ice volume in the arctic varies throughout a typical year from its maxima in March to its minima in September (Serreze, 2007). In 2005, the minima was a 21% reduction from the average from 1979 through 2000. The reduction is ice area was comparable to the size of Alaska (Serreze, 2007). In 2005, a piece of ice the size of Manhattan broke free from a Canadian ice shelf and there is concern that it could float into shipping lanes and oil production regions (Williams, 2007). Within 50 years, the amount of Arctic ice during summers may be sufficiently reduced to allow shipping through the Arctic (Speth, 2004; Blatt, 2005).
Greenland has been losing between 50 and 100 gigatons of ice per year since 1993 (IPCC, Document I, 2007). The thickness of ice in Greenland is decreasing by about 3 feet a year. In 2005, the extent of ice melt in Greenland was the greatest that had ever been recorded and covered a far greater area than in 1992 (Blatt, 2005, Union of Concerned Scientists, 2007). During the period of 2003 to 2005, the Greenland ice sheet lost more than 110 gigatons of ice per year (Luthcke, 2006). Tourists now visit ‘ Warming Island’ an island which until recently was hidden under the Greenland ice sheet (Williams, 2007). If the Greenland ice sheet were to melt completely, sea levels would rise by about 23 feet (IPCC, 2007).
Glacial ice is melting. A large amount of water is trapped in glaciers on mountains and in permafrost areas close to the poles. Much of this ice is melting as well. In 1992, it was reported that all mid- and low-latitude glaciers were retreating and the ice record within these glaciers indicated that this is the warmest 50 years of any in the past 12,000 years (Laidre, 2005). In every major mountain chain in the Northern Hemisphere, the freezing altitude is higher than in the past. Snow cover in mountains has dropped by 5% (Union of Concerned Scientists, 2007). Since 1900, the land area covered by permafrost has decreased by 7% year-round and by 15% in spring (IPCC, Document I, 2007; Blatt, 2005). All the glaciers of Glacier National Park in the United States are expected to disappear in this century (Blatt, 2005). About 85% of the snowfields in the Western U.S. have decreased their volume since the 1950s. The famous snows of Mt. Kilimanjaro in Africa may be gone by the years 2010-2020. This mountain has already lost glaciers which were once thousands of feet thick. Mt Everest is 4 feet shorter than it once was and its glacier has retreated three miles. The Eastern Himalayas have lost 20% of their glaciers in the past century and all the glaciers may be gone by the year 2035. In some areas, the glaciers retreat 500 feet per year (Bowen, 2005). High mountain ecosystems are experiencing a retreat of glaciers, a reduction in lake size, and a loss of biodiversity (Ruiz, 2008). A number of smaller tropical glaciers are expected to be lost within the next few decades (Vuille, 2008; Gordon, 2008).
More than one sixth of the global population receives a significant amount of their water supply from seasonal glacier and snow melt. Without this frozen water supply, many areas will pass more water on to oceans and have less for human use (Barnett, 2005).
Throughout the majority of the history of the earth, the global temperature was higher than it is today, there were no polar ice caps, and sea level was higher than it is today. For example, in the mid-Cretaceous Period, much of the East Coast was underwater and an inland sea covered much of the interior of the North America. If all the earth's ice were to melt, sea level would increase 150 feet and 15% of the U.S. would be underwater including the entire states of Massachusetts, Connecticut, Rhode Island, New Jersey, Delaware, Florida, and Louisiana and the cities of New York, Philadelphia, Miami, Seattle, and San Francisco (Blatt, 2005). Warm water takes up more space than cold water. As global temperatures rise, the ocean temperature rises, causing ocean expansion and the sea level rise.
By the end of the 21st century, the rise in sea level is expected to impact the lives of millions of people. In the 21st century, the global temperature is predicted to increase between 1.4 and 5.8 degrees Celsius which would increase sea level somewhere between 9 and 88 centimeters (IPCC, 2001). During the period of 1993 to 2003, sea level rose at a rate of 3.1 mm per year. Sea level is expected to rise between .18 and .59 meters by the end of this century. (IPCC, Document I, 2007; Meier, 2007). An increase of 25 cm would have serious consequences on the delta regions of the Nile, Ganges, and Yangtze Rivers and would require the evacuation of many small island nations of the Indian Ocean and the Pacific. A one meter rise in sea level increase would flood many coastal areas, such as the beaches of the eastern United States. Florida, Louisiana, and North Carolina would be most affected; the Louisiana coast could lie 30 miles inland of its present location. A number of cities such as Venice, Bangkok, and Taipei would be threatened. Eighty percent of the Marshall Islands would be underwater. A one meter increase would flood up to 15% of the arable land in Egypt, 11% of the land of Bangladesh (where the floods of 1987-8 displaced millions of people), and require the raising of most of Miami's bridges and reconstruction costs to 1/3 of Miami's area. More than 100 million people would be displaced. Some coastal areas depend on underground freshwater aquifers (such Miami) which would be threatened by saltwater intrusion (IPCC, 1990; Mizra, 2002).
Rising seas would threaten global commerce. Ninety percent of the transport of global merchandise occurs by sea. Some countries, such as Brazil, Chile, and Peru, utilize sea travel for more than 95% of their exports. In 2005, the global merchant fleet increased by 7.2% (IPCC, Document III, 2007).
4) WEATHER CHANGES AND EXTREME WEATHER
In the U.S., flooding causes $6 billion in damages annually. The floods throughout the Midwest in the summer of 1993 cost $16 billion in damages. During this time the Mississippi (pictured below) rose 46 feet over its normal level and three feet over its record level (Blatt, 2005).
About 60% of the country of Bangladesh is less than 20 feet above sea level and is vulnerable to seasonal floods. On average, about 21% of Bangladesh is flooded per year with as much as 70% in severe floods. As a result of global warming, Africa will experience higher levels of desertification and additional droughts and floods. Asia will experience an increase in the number of tropical cyclones which will displace tens of millions of people (IPCC, 2001). There has been a significant increase in the number of heavy precipitation events, droughts (especially in the tropics and subtropics) and tropical cyclone activity.Between 1999 and 2003, many areas of central Asia experienced extreme drought, the worst in 50 years. By June 2000, some areas of Iran had gone without rain for 30 months. The drought in the Western U.S. in recent years is the second most extensive and one of the longest in the past century Flooding in Europe in the summer of 2002 included the Elbe cresting 9.4 meters above normal, the highest point since records were kept in the year 1275 (IPCC, Document I, 2007).
Warmer temperatures lead to increases in the number and severity of hurricanes. When the surface temperature of ocean water increases 1oF, the risk of hurricanes doubles. Forty five million Americans live in coastal areas vulnerable to hurricanes (Blatt, 2005). Recent years have seen an increase in the number of hurricanes and tropical storms and nine of the past 11 years have witnessed above average numbers of hurricanes. In 2003, three simultaneous hurricanes existed in different regions of the Caribbean and Atlantic; this was the first time such an event was observed. In 2004, a record number of hurricanes (four) hit Florida. The first recorded tropical cyclone in the south Atlantic occurred in 2004. In 2005, the hurricane season began earlier than ever before, ended later than ever before, and witnessed the greatest number of hurricanes and tropical storms (26 named storms including 3 which reached Category 5 strength). In 2005, hurricane Katrina (which was a Category 5 storm just before landfall) flooded New Orleans, costing more than 1,300 lives and $125 billion in damage. The recent increase in the number of strong tropical cyclones in the North Pacific has been attributed to global warming (Stowasser, 2007). The damage done to Gulf Coast forests by hurricane Katrina resulted in a loss of sequestered carbon about equal to the annual carbon sequestration by all U.S. forests (Chambers, 2007).
The onset of spring continues to occur earlier throughout the world but this change is greatest in high arctic areas such as Greenland (Hoye, 2007). The freezing of lakes and rivers in the Northern Hemisphere occurs an average of 5.8 days later in winter and 6.5 days earlier in spring when compared to a century ago (IPCC, 2007).
ICE AGES AND THE CLIMATE OF EARTH'S PAST
For the majority of the past 500 million years, the earth's climate has been significantly warmer than modern times. For the majority of this period tehere were no polar ice caps and sea level was higher. The earth’s climate of the period prior to 2.6 million years ago was typically warmer than it is today. Three million years ago, the temperature is estimated to have been 2 to 3 degrees warmer than modern times (IPCC, Document I, 2007). It is possible to estimate global climatic conditions from the past 650,000 years from the ice and air trapped with ice sheets. The isotopes ratios of certain elements in rocks (such as oxygen) can allow estimates of more ancient time periods. Since ice sheets leave traces on underlying rock, it is possible to estimate the extent of past glaciations. Combined data indicate that the earth has been warmer and completely devoid of ice sheets for most of the past 500 million years (IPCC, Document I, 2007).
Louis Agassiz first proposed the possibility of Ice Age in 1837. A series of Ice Ages occurred over the past 1.5 million years. In North America, two ice sheets formed: one originating in the Northwest Rocky Mountains (the Cordilleran ice sheet) and another originating around the Hudson Bay (the Laurentide ice sheet). When the glaciations reached their greatest extent, these two ice sheets joined and formed an ice area of 6 million square miles—an area greater than the ice of Antarctica and possibly representing the largest ice sheet to ever form in earth’s history. Ice sheets also covered parts of Europe, Asia, Greenland, Antarctica, and the southern regions of South America, Africa, and Australia. Because so much water was locked up in ice sheets, sea level dropped an estimated 300 feet. As a result, many regions which are currently covered by ocean were exposed such as an ice-free land bridge which connected Alaska and Siberia (the land bridge is referred to as Beringia) (Kurten, 1988).
The Late Tertiary was cooler than the earlier part had been and a variation of cooler and warmer periods occurred although the magnitude was less than the more recent glaciations and interglacial periods. In the past 1.5 million years, a series of glaciations were interrupted by interglacial periods of comparable warmth. The Nebraskan Glaciation began 1.5 million years ago and ended about 1.1 million years ago. After the Aftonian interglacial period, the Kansan Glaciation began about 900,000 years ago and ended about 600,000 years ago. Following the Yarmouthian Interglacial, the Illinoian Glaciation began about 600,000 years ago and ended 100,000 years ago. After the Sangamonian interglacial period, the Wisconsonian Glaciation began about 100,000 years ago and ended only recently (about 10,000 years ago). The last interglacial period lasted 11,000 years and the prior interglacial period lasted 16,000 years. Since it has been 10,000 years since the last glaciation ended, the current period might be another interglacial period which will end in another Ice Age. The alternation between glacial and interglacial periods is largely due to variations in the earth’s orbit (which changes regularly from elliptical to circular over a period of about 100,000 years), the tilt of the earth’s axis (which changes over a period of about 41,000 years), and the variation of the time period in which the earth is closest to the sun (the precession of the equinox) (Kurten, 1988). Pollen studies indicated climate changes in Greenland including a spruce filled boreal forest which existed about 400,000 years ago (De Vernal, 2008).
During the last interglacial period (130 to 116 thousand years ago), there was less ice on earth than there is today. During the glacial and interglacial periods, more than 20 abrupt climatic changes have been recorded. For example, the Dansgaard-Oeschger events included an 8 degree Celsius temperature increase in Greenland over a few decades. The Heinreich events were rapid periods of warming in which ice sheet melting in the North Atlantic led to sea level rises of up to 15 meters and dramatic changes of the major currents. Sea level during the last glacial maximum was 140 feet below modern sea level. About 8,200 years ago, a sudden drop of temperature of 2 to 6 degrees Celsius apparently resulted from a reorganization of the Atlantic’s MOC following the massive release of 10 14 cubic meters of water from melting glaciers in the Hudson Bay area (the postglacial “Lake Agassiz”) (IPCC, Document I, 2007).