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22561429-IBWG-Climate-Change-Notes -...

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Unformatted text preview: http://guidesbyjulie.blogspot.com/ IB World Geography Climate Change Climates naturally vary from place to place Climates also vary over time The world’s climate maps are based place. time. on averages over periods of a few decades of the mid- 20th century However, the world climate map has not midcentury. century always looked like this. Considerable change has taken place over the years, and will continue in the future. Humans have long been able to modify their environments sometimes radically, by building settlements environments, settlements, clearing forests for agriculture domesticating animals manufacturi ng goods, damming rivers, and spreading agriculture, animals, manufacturing waste through the air and seas across the land. The Earth’s land surface is profoundly different today from what it was only 200 years ago. For example, the forests of the eastern United States were almost completely completely 1900, Plains, removed between 1600 and 1900 and an entire ecological community, the Great Plains has been replaced by agricultural crops since 1800. Only recently has anyone attempted to make a link between humankind’s modifications of the Earth’s surface, and global -scale climate changes global balchanges. The entirety of geological time is about 4.6 billion years The last 2 million years have been what geologists call years. the Quaternary Period The Earth has experienced more climatic variability during this time than in most of the Period. previous 200 million years. Climate during the Quaternary Period has included periods in which global average temperature was as much as 18 degrees cooler than the present and warm intervals that were much warmer than the present. In the last 1 million years there have been about 10 of these cold intervals occurring regularly about once every 100,000 intervals, years. During these cold intervals, great continental ice sheets covered most of the Northern Hemisphere These Hemisphere. periods of glaciations were also periods of lowered sea level because precipitation was taken out of the sea level, and stored on land in the form of glacial ice This portion of the Quaternary Period in which glaciers occurred is ice. called the Pleistocene Epoch In our everyday language, we call these periods Ice Ages Epoch. Ages. The climate shifted between warm and cool periods between 10 and 30 times during the Pleistocene Epoch The Epoch. exact number is not known. The last period reached this maximum as indicated by the extent of glacial ice only about 180,000 years ago; well within the human archaeological record. The melting of the ice back to its . present extent was completed about 9,000 years ago. Climatic fluctuations during the Pleistocene Epoch (2,000,000 to 10,000 years ago) caused glaciers to grow and decay. As the last ice sheet that covered British Columbia retreated at the end of the Pleistocene, it left behind many distinctive landforms and sediments. During the last glaciation, east-flowing glaciers scoured the bedrock and deposited till a poorly till, sorted sediment containing stones up to boulder size. Till blankets flat to moderately sloping terrain above the valley floor. Elongate and spoon-shaped hills of glacial debris (drumlins are oriented drumlins) drumlins parallel to the direction of glacier flow. http://guidesbyjulie.blogspot.com/ IB World Geography Climate Change Streams of meltwater flowed through tunnels within, beneath, and on the glaciers. Sand and gravel accumulated in these tunnels, forming long, narrow, sinuous ridges (eskers The ridges are an excellent source of sand and eskers). eskers gravel. Where meltwater streams flowed away from the ice front, they deposited sand and gravel as outwash plains. fans and outwash plains Isolated and buried ice blocks in the outwash melted to form depressions known as kettles. lakes. kettles Meltwater was also dammed in places by ice or sediments, forming glacial lakes When the ice sheet disappeared, the lakes drained, leaving behind nutrient-rich silty and clayey sediments that form some of the best agricultural land in central British Columbia. Within the past 1,000 years, the climate has varied, though less dramatically than in the distant past. Recent climate changes shave been important in European history. Between A.D. 800 and 1,000 sea-faring pirates and 1,000, adventurers from present day Scandinavia called the Vikings extensively explored the North Atlantic Ocean Scandinavia, Vikings, and established settlements in Greenland and North America Lack of sea ice during this exploration period was America. a result of especially warm temperatures which aided the Vikings exploration and farming of the far North. temperatures, Ages, 1,200. 1500Cooling occurred in the Middle Ages beginning about 1,200 The period from about 1500-1750 is known as the Age. Europe, America, Asia. Little Ice Age Glaciers advanced in Europe North America and Asia Since the early 1800s and especially 1900, after 1900 climates have warmed steadily. Most of the Earth’s glaciers have been shrinking since the early 1800s. There has been some significant cooling periods though, such as the time period of 1884-1887 caused periods, 1884by the eruption of the volcanic island of Krakatau in Indonesia The amount of ash and sulfur dioxide into the Indonesia. atmosphere was so thick that it prevented some of the sun’s short-wave rays from reaching the Earth’s shortsurface. The 1930 s and 1940s were relatively warm then cooling occurred from about 1945 to 1970 Climate has 1930s warm, 1970. 1975. warmed increasingly since 1975 It is important that these major fluctuations have occurred well within the period of human occupation of Earth. Glacial meltdow n from the most recent ice age was particularly rapid meltdown about 15,000 to 10,000 years ago. Archaeologists have discovered that agriculture and cities probably developed about 10,000 to 8,000 years ago. Many scholars of early human culture believe climate change was fundamental to the development of civilizations influencing the availability of water for crops and perhaps civilizations, driving major migrations migrations. The period of glacial melting and warming between 15,000 to 5,000 years ago coincided with expansion of human settlement in northern Europe and North America. Settlement extended gradually northward into the settlement America European mainland and became well established in the British Isles by 2,000 B.C. Meltwater from the glaciers raised sea level, flooding low-lying areas and separating land areas. Water filled the English Channel, isolating level separating areas Channel the British Isles from Europe, and “Beringia” the land bridge that connected North America to Asia went underwater, halting migration from Asia into North America. This rising sea level also led to rapid filling of the Black Sea about 7,500 years ago. ...
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