Deserts,_Glaciers_and_Climate

Deserts, Glaciers and Climate Deserts and glaciers are the two most disparate examples of Earth’s climate. However, they are linked not only by their diverse beauty and extreme climates, but also by severe erosional forces and by the fact that they are possibly the most important indicators of Earth’s climate changes. Deserts are not necessarily just the barren oceans of sand, such as the Sahara Desert of Northern Africa, which has figured so prominently in movies and on television. There are also polar deserts, where the snow builds up into thick ice sheets the way sand can build up into enormous dunes. According to the Merriam-Webster dictionary, the definition of the word “desert” is “an arid land with usually sparse vegetation and receiving less than 25 centimeters of rainfall annually”. The ice sheets that form over large areas of land, such as those located at the North and South poles, Greenland and Antarctica, are also considered continental glaciers. Both deserts and glaciers create landforms by erosion and by deposition. In the desert, landforms such as sand dunes, mesas, and buttes are formed by erosion and deposition – the wind picks up fine, loose particles of sand and gradually erodes the softer surfaces of large rock, forming them into angular, fantastic rock formations. The larger, heavier particles are deposited in depressions in the ground or sheltered areas near cliffs to form sandy dunes. The dunes of the Sahara desert are also formed by wind. Dune formation is also called surface-creep. This is the transportation of particles of sand along the ground by wind. In the glacial environment, landforms are also created by erosion and deposition. As the glacier moves along the ground, the weight and movement of the ice scrapes the material beneath it, leaving marks as small as a scratch on a rock, or gouging out areas as large as a lake. The material that is eroded by the ice is carried along with it and is eventually dropped, or deposited, somewhere else. This deposition can be either from the material being deposited in the melt water of the glacier or by it dropping out of the ice. These depositions form landforms known as tills, which are a mixture of crushed rock, sand, pebbles, and rocks of various sizes; and moraines, which are ridges or piles of debris. The Earth’s climate has been changing for millions of years. From the several Ice Ages where extremely large portions of the Earth were covered in ice and snow, thru the interglacial periods when the glaciers and ice packs retreated or melted completely – the climate has been in a continuous state of change over the last two million years. By studying and analyzing surrogate, or “proxy”, measures of climate – these include ice cores pulled from deep within glaciers, glacier lengths, ocean and land sediments, tree rings, and even fossilized pollen spores – scientist can give us a picture of Earth’s climate up to 100 million years ago. They also study things such as the change in Earth’s orbit around the sun. The shape – or eccentricity – of our planet’s orbit, as well as the plant’s tilt, affects the amount of sunlight the Earth’s surface receives. This is thought to be one of the main causes of ice ages according to the theory of a Serbian mathematician, Mulitin Milankovitch. Changes in the sun’s intensity, volcanic eruptions, changes in greenhouse gas concentrations, and changes in ocean currents are also studied as measures of climate. For approximately the last 2000 years, Earth has been in warming period, also known as an interglacial period, and the climate has been relatively stable. There have been three relatively short periods that have been anomalous to this climactic stability. These periods have been the Medieval Climate Anomaly which occurred approximately between 900 and 1300 AD. Evidence suggest that Europe, Greenland, Asia and the American West experienced warmer, drier conditions than other areas of the planet experienced during the same period. Evidence exists of a global “Little Ice Age” that occurred between 1500 and 1850 AD. And within the past 100 years, an additional warming period has occurred. This period coincides with the beginning of the Industrial Era and the rapid addition of greenhouse gases that this has caused. Scientists have discovered that over the past 100 years, the temperature over the land and the ocean areas has risen approximately 0.5 degrees Celsius. They estimate that if the current trend continues, temperatures could warm again by over 1 degree Celsius. If this holds true, then the climate shift we could possibly see in the 21st century would be drier, hotter desert climates with the desert areas of the Earth expanding while the glaciers would melt as the colder regions of the Earth warm, shrinking the expanse of the polar glaciers and ice sheets. References Visualizing Geology http://www.merriam-webster.com/dictionary/desert http://www.scienceclarified.com/landforms/Faults-to-Mountains/Glacial-Landforms-and-Features.html http://ccir.ciesin.columbia.edu/nyc/pdf/q1b.pdf http://www.epa.gov/climatechange/science/pastcc.html http://earthobservatory.nasa.gov/Features/Milankovitch/[pic][pic]