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UNM ENVS 101 - Earth's Climatic Change, and Why Climates Change
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ENVS 101 1st Edition Lecture 22 Outline of Last Lecture I. Earth’s Climatic System II. Evidence of climatic ChangeOutline of Current Lecture II. Evidence of Climatic ChangeIII. Why Climates ChangeCurrent LectureThroughout nature, there are various other organisms that act as climate proxies to help scientists study the climate of the Earth. Organisms that lay down annual growth rings such as trees and corals are commonly used to study climate change, as well as some lake sediments which form pairs of layers that are deposited in a single year, (known as varves). Deep sea sediment is another proxy, as cores of this particular sediment contain fossils of foraminifera, which are small surface dwelling organisms. Lake and ocean sediments also contain pollen from nearby plants, and speleothems (cave formations) are also proxies, which contain datable growth layers.Climate of the past millennium included a Little Ice Age that took place around 400-150 years ago, in which temperatures throughout Western Europe were 1-2oC cooler than they are today, as well as a lowering of the world’s snowline by about 100 meters. There was also a time period known as the Medieval Warm Period, which was an episode of relatively mild climate that took place about 800 years ago.The last glaciation took place around 70,000 to 10,000 years ago. The maximum ice sheet extentwas about 24,000 years ago by comparison. During the last glaciation, sea level fell 120 meters or so, which ended up exposing continental shelves, allowing the ice sheets to spread over those as well.During this time period, global temperatures were up to 8o C cooler, but despite this change, thetropics region had been the least affected by the cold changes in temperature, due to their location along the Equator of the Earth. The greatest cooling that took place was near the large ice sheet near the upper region of North America. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.The last glaciation/ Pleistocene Epoch: at the height of the glacial age, middle latitudes were windier and dustier than they are today. Reduced precipitation was likely du to reduced evaporation occurring within the environment. Pollen studies show a very different vegetation distribution than today. Species of the Earth were displaced in various directions, forming new plant communities. In Europe, various specieswere driven to the point of extinction, and the continent now has only 30 different naturally occurring trees. Compare this to the variety of naturally occurring of trees found in North America, which is about 150 different trees by contrast.For the majority of the last 800,000 years the average length of a glacial-interglacial cycle was 100,000 years. Prior to this time period, the duration of each cycle averaged only about 40,000 years. Why climates change: There are external causes, such as solar variation. There is an elven year sun spot cycle which takes place, which is a temporary cool dark spot on the Sun, surrounded byhotter areas. This increases overall solar luminosity. At the Maunder minimum, there are few sunspots, which means cooler climate as a result. Earth’s orbit and tilt influence the distribution of solar radiation, which in turn brings about the seasons. Bear in mind that the seasons are flipped in the southern hemisphere, so the time period that we consider the summer solstice is their winter solstice, and vice versa. Milankovitch cycles are minor variations in the Earth’s orbit around the Sun and in the tilt of the Earth’s axis. Eccentricity: The shape of the Earth’s orbit becomes more circular or more oval (eccentric), thus the Earth’s orbit is nearly a perfect circle. 100,000 year time period is the average time in which this cycle takes place. This time period is also the same as recent major glaciations that have occurred on the Earth. Obliquity: Earth’s axis tilts at an average angle of 23.5o and shifts about 1.5o to either side. This process takes place over a time period of 41,000 years, which happens to match up with the duration of some of the earlier glacial cycles which have taken place on


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UNM ENVS 101 - Earth's Climatic Change, and Why Climates Change

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