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17-08-2020
Milankovitch Cycles and Global Climate Changes
Question 1 (25 pts): Enter coordinates 49°18′28′′N 87°35′41′′E into Google Earth. Turn on “Photos” in the Google Earth “Layers”. Look for photos as close to the given coordinates as you can. Using the Köppen climate classification system, describe the vegetation, climate, geographic location (i.e. maritime, continental, etc.), and any other evidence observable to describe the climate of this place. You may use readings and the internet, and if any information is used besides Google Earth or Google Maps, then please cite within text. Please answer as a short essay using a minimum of 4-6 paragraphs. Use terminology learned during the term, with emphasis on the second half of the term.
The Milankovitch cycles describe how relatively slight changes in Earth’s movement affect the planet’s climate. The cycles are named for Milutin Milankovitch, a Serbian astrophysicist who began investigating the cause of Earth’s ancient ice ages in the early 1900s, according to the American Museum of Natural History (A.M.N.H). To determine how Earth could experience such vast changes in climate over time, Milankovitch incorporated data about the variations of Earth’s position with the timeline of the ice ages during the Pleistocene. He studied Earth’s variations for the last 600,000 years and calculated the varying amounts of solar radiation due to Earth’s changing orbital parameters. In doing so, he was able to link lower amounts of solar radiation in the high northern latitudes to previous European ice ages, according to AMNH. Milankovitch’s calculations and charts, which were published in the 1920s and are still used today to understand past and future climate, led him to conclude that there are three different positional cycles, each with its own cycle length, that influence the climate on Earth: the eccentricity of Earth’s orbit, the planet’s axial tilt and the wobble of its axis.
Eccentricity. The Earth orbits the sun in an oval shape called an ellipse, with the sun at one of the two focal points (foci). Ellipticity is a measure of the shape of the oval and is defined by the ratio of the semiminor axis (the length of the short axis of the ellipse) to the semimajor axis (the length of the long axis of the ellipse), according to Swinburne University. A perfect circle, where the two foci meet in the center, has an ellipticity of 0 (low eccentricity), and an ellipse that is being squished to almost a straight line has an eccentricity of nearly 1 (high eccentricity). The Earth’s orbit slightly changes its eccentricity over the course of 100,000 years from nearly 0 to 0.07 and back again, according to NASA’s Earth Observatory. When the Earth’s orbit has a higher eccentricity, the planet’s surface receives 20 to 30 percent more solar radiation when it’s at perihelion (the shortest distance between the Earth and sun each orbit) than when it is at aphelion (the largest distance between the Earth and sun each orbit). When the Earth’s orbit has a low eccentricity, there is very little difference in the amount of solar radiation that is received between perihelion and aphelion. Today, the eccentricity of Earth’s orbit is 0.017. At perihelion, which occurs on or around Jan. 3 each year, Earth’s surface receives about 6 percent more solar radiation than at aphelion, which occurs on or around July 4.
Axial tilt. The tilt of the Earth’s axis relative to the plane of its orbit is the reason that we experience seasons. Slight changes in the tilt changes the amount of solar radiation falling on certain locations of Earth, according to Indiana University Bloomington. Over the course of about 41,000 years, the tilt of the Earth’s axis, also known as obliquity, varies between 21.5 and 24.5 degrees. When the axis is at its minimal tilt, the amount of solar radiation doesn’t change much between summer and winter for much of Earth’s surface and therefore, seasons are less severe. This means that summer at the poles is cooler, which allows snow and ice to persist through summer and into winter, eventually building up into enormous ice sheets. Today, the Earth is tilted 23.5 degrees, and slowly decreasing, according to EarthSky.
Precession. Earth wobbles just slightly as it spins on its axis, similarly to when a spinning top begins to slow down. This wobble, known as precession, is primarily caused by the gravity of the sun and moon pulling on Earth’s equatorial bulges. The wobble doesn’t change the tilt of Earth’s axis, but the orientation changes. Over about 26,000 years, Earth wobbles around in a complete circle, according to Washington State University. Now, and for the past several thousands of years, Earth’s axis has been pointed north more or less toward Polaris, also known as the North Star. But Earth’s gradual precessional wobble means that Polaris isn’t always the North Star. About 5,000 years ago the Earth was pointed more toward another star, called Thubin. And, in approximately 12,000 years, the axis will have traveled a bit more around its precession circle and will point toward Vega, which will become the next North Star.
Long term global climate change is a term used to refer to the adverse effects of the change of global climates due to human activities. Scientists have predicted that long-term effects of climate change will include a decrease in sea ice and an increase in permafrost thawing, an increase in heat waves and heavy precipitation, and decreased water resources in semi-arid regions. This long term global climate change is a process that has occurred in the past and has gone on to develop and morph into something greater and more dangerous due to the activities and negligence of humankind. It is also imperative that it will go on in the future if decisive measures are not taken in order to halt environmental degradation which brings about long term global climate change.
Global climates refer to the long-term distribution of heat and precipitation on Earth’s surface. Heat from the sun keeps the Earth’s average temperature at about 60°F (16°C), within a range that allows for biological life and maintains the planet’s life-sustaining reservoirs of liquid water. Astronomical variations and atmospheric shielding cause incoming solar radiation to fall unevenly on the Earth’s surface. A complex group of astronomical, atmospheric, geological, and oceanographic factors account for Earth’s global climate. Many of these factors vary naturally over decades, centuries, and millennia. Furthermore, astronomical and geological variations begin a cascade of compensatory adjustments in the coupled, or linked, ocean-atmosphere system, which, in turn, require major adjustments to biological systems. These variations force changes in the global pattern of long-term precipitation and temperature, or global climate change. Global climate change causes permanent redistribution of climatic zones, alteration of major weather patterns, and establishment of new ecosystems. Global climate change has occurred throughout Earth’s history, and has been a major driving force in biological evolution; species unable to adapt to new climate regimes have become extinct, while others have flourished. Scientists predict that human activities, notably combustion of carbon-based fossil fuels like oil and coal, will affect the climate-regulating properties of the atmosphere, which may cause anthropogenic (human-induced) global climate change.
Glaciers are made up of fallen snow that, over many years, compresses into large, thickened ice masses. Glaciers form when snow remains in one location long enough to transform into ice. What makes glaciers unique is their ability to flow. Due to sheer mass, glaciers flow like very slow rivers. Some glaciers are as small as football fields, while others grow to be dozens or even hundreds of kilometers long. Presently, glaciers occupy about 10 percent of the world’s total land area, with most located in Polar Regions like Antarctica, Greenland, and the Canadian Arctic. Glaciers can be thought of as remnants from the last Ice Age, when ice covered nearly 32 percent of the land, and 30 percent of the oceans. Most glaciers lie within mountain ranges that show evidence of a much greater extent during the ice ages of the past two million years, and more recent indications of retreat in the past few centuries. An ice cap is a dome-shaped glacier mass flowing in all directions, such as the ice cap on Ellesmere Island in the Canadian Arctic. An ice sheet is a dome-shaped glacier mass exceeding 50,000 square kilometers. The world’s ice sheets are confined to Greenland and Antarrctica.
Weathering, disintegration or alteration of rock in its natural or original position at or near the Earth’s surface through physical, chemical, and biological processes induced or modified by wind, water, and climate. With weathering, rock is disintegrated into smaller pieces. Once these sediments are separated from the rocks, erosion is the process that moves the sediments away from it’s original position. The four forces of erosion are water, wind, glaciers, and gravity. Water is responsible for most erosion. Water can move most sizes of sediments, depending on the strength of the force. Wind moves sand-sized and smaller pieces of rock through the air. Glaciers move all sizes of sediments, from extremely large boulders to the tiniest fragments. Gravity moves broken pieces of rock, large or small, down slope. These forces of erosion will be covered later. While plate tectonics forces work to build huge mountains and other landscapes, the forces of weathering and mass wasting gradually wear those rocks and landscapes away, called denudation. Together with erosion, tall mountains turn into hills and even plains.
Astronomers define the reflectivity of an object in space using a term called albedo. This is the amount of electromagnetic radiation that reflects away, compared to the amount that gets absorbed. A perfectly reflective surface would get an albedo score of 1, while a completely dark object would have an albedo of 0. Of course, it’s not that black and white in nature, and all objects have an albedo score that ranges between 0 and 1. Here on Earth, the albedo effect has a significant impact on our climate. The lower the albedo, the more radiation from the Sun that gets absorbed by the planet, and temperatures will rise. If the albedo is higher, and the Earth is more reflective, more of the radiation is returned to space, and the planet cools. An example of this albedo effect is the snow temperature feedback. When you have a snow covered area, it reflects a lot of radiation. This is why you can get terrible sunburns when you’re skiing. But then when the snow covered area warms and melts, the albedo goes down. More sunlight is absorbed in the area and the temperatures increase. Climate scientists are concerned that global warming will cause the polar ice caps to melt. With these melting caps, dark ocean water will absorb more sunlight, and contribute even more to global warming.
Earth observation satellites are constantly measuring the Earth’s albedo using a suite of sensors, and the reflectivity of the planet can actually be measured through Earthshine – light from the Earth that reflects off the Moon. Different parts of the Earth contribute to our planet’s overall albedo in different amounts. Trees are dark and have a low albedo, so removing trees might actually increase the albedo of an area; especially regions typically covered in snow during the winter. Clouds can reflect sunlight, but they can also trap heat warming up the planet. At any time, about half the Earth is covered by clouds so their effect is significant. Needless to say, the albedo effect is one of the most complicated factors in climate science, and scientists are working hard to develop better models to estimate its impact in the future. The most significant impact of the albedo effect in the Earth-sciences is its projected present and future effects on global warming. With the consistent melting of ice and snow on the Earth’s surface due to a rise in global mean temperatures, white surfaces globally are decreasing in area. This is steadily decreasing the amount of the Sun’s energy reflected back into space, leading to even greater warming of the Earth due to the trapping of heat.
The albedo effect is thus creating a positive feedback loop, especially in the case of Arctic ice, where the ice is melting and the resultant increase in heating is aggravating even more melting of ice and so on. Even when the ocean water is exposed to sunlight, the warming of the water can cause the ice to melt from beneath. The melted ice produces more water, which adds to this melting effect. This doubles the action of melting in the Arctic regions where ice melts both due to action from below and due to increased surface temperatures due to increased greenhouse gas emissions. Even an increased amount of cloud cover would mean increased water vapour, which is a greenhouse gas, contributing to the positive feedback loop of global warming (G.P. Wayne, 2016). The albedo of a surface is measured on a scale alternating between 0 to 1, with o being the ultimate dark surface with full absorption and 1 being the ultimate bright surface with full reflection of incident light energy. The albedo measurement for sea is o to 0.1, for forests is between 0.1 to 0.2, for soil is between 0.1 to 0.25, for grass is 0.15 to 0.25, for desert is between 0.25 to 0.4, and for dry snow is between 0.75 to 0.95 (National Learning Centre for Remote Sensing, undated).
Lawrence C. Nkemdirim from the University of Calgary, Canada accumulated data on measurements of albedo on various surfaces and published his study in the paper titled ‘A Note on the Albedo of Surfaces’. Nkemdirim carried out his measurements using devices called solari-albedometers in conjunction with a computerized data acquisition system. His inferences were based on average albedo out of variations in the inclination of the Sun and general cloudiness. After taking various variables such as cloudiness and the inclination of the Sun into account, Nkemdirim choose his site as a partially cropped potato farm located in a flat praire. As such irrigation was also a factor as it is responsible for moisture. The location makes a difference and although measurements might vary slightly, certain relative values can be ascertained. The co-ordinates for the location were 51oN and 114oW, with an elevation of 1080 m from sea level. Taking observations over many days, Nkemdirim found that in spite of the symmetry in global solar radiation, a great amount of diurnal variance was observed for albedo, which is incredibly relevant for energy budget studies.
In Nkemdirim’s experiment, non-irrigated potatoes displayed a greater albedo effect as the ability to reflect back the Sun’s energy, while the moist irrigated potatoes displayed a slightly lesser albedo effect, most probably due to the presence of excess water vapour, which is a greenhouse gas. Their albedo measurements varied also according to the inclination of the Sun and general cloudiness (L.C. Nkemdirim, 2000). Thus they were able to perceive how less solar heat is reflected back in the presence of greenhouse gases, which act to absorb solar heat, trapping them within the Earth’s atmosphere. They also noted how the albedo effect is dependent on the location and its various specificities as also the inclination of the Sun at a particular location and general cloudiness, although the quality of global solar radiation was more or less the same. Besides the warming and cooling of the Earth, the albedo effect can also have an influence on the general climate of the Earth. The effect of changes in albedo can influence rainfall, and in a study on semi-arid regions in North America, Africa and Asia carried out by Jule Charney, the patterns of evaporation were studied to see how an increase in the albedo effect led to a decrease in convective clouds and precipitation. Charney found that an increase in albedo effect led to a huge decrease in rainfall in the regions when it was accompanied by a lack of local evaporation.
Record floods. Raging storms. Deadly heat. Climate change manifests itself in myriad ways, and it’s the ultimate equalizer: a challenge faced by every living being. Here are the basics on what causes climate change, how it’s affecting the planet, and what we can do about it. Climate change is a significant variation of average weather conditions—say, conditions becoming warmer, wetter, or drier—over several decades or more. It’s that longer-term trend that differentiates climate change from natural weather variability. And while “climate change” and “global warming” are often used interchangeably, global warming—the recent rise in the global average temperature near the earth’s surface—is just one aspect of climate change. Earth-orbiting satellites, remote meteorological stations, and ocean buoys are used to monitor present-day weather and climate, but it’s paleoclimatology data from natural sources like ice cores, tree rings, corals, and ocean and lake sediments that have enabled scientists to extend the earth’s climatic records back millions of years. These records provide a comprehensive look at the long-term changes in the earth’s atmosphere, oceans, land surface, and cryosphere (frozen water systems). Scientists then feed this data into sophisticated climate models that predict future climate trends—with impressive accuracy.
The mechanics of the earth’s climate system are simple. When energy from the sun is reflected off the earth and back into space (mostly by clouds and ice), or when the earth’s atmosphere releases energy, the planet cools. When the earth absorbs the sun’s energy, or when atmospheric gases prevent heat released by the earth from radiating into space (the greenhouse effect), the planet warms. A variety of factors, both natural and human, can influence the earth’s climate system. Natural causes of climate change. As we all know, the earth has gone through warm and cool phases in the past, and long before humans were around. Forces that contribute to climate change include the sun’s intensity, volcanic eruptions, and changes in naturally occurring greenhouse gas concentrations. But records indicate that today’s climatic warming—particularly the warming since the mid-20th century—is occurring much faster than ever before and can’t be explained by natural causes alone. According to NASA, “These natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades.”
Humans—more specifically, the greenhouse gas (GHG) emissions we generate—are the leading cause of the earth’s rapidly changing climate. Greenhouse gases play an important role in keeping the planet warm enough to inhabit. But the amount of these gases in our atmosphere has skyrocketed in recent decades. According to the Intergovernmental Panel on Climate Change (IPCC), concentrations of carbon dioxide, methane, and nitrous oxides “have increased to levels unprecedented in at least the last 800,000 years.” Indeed, the atmosphere’s share of carbon dioxide—the planet’s chief climate change contributor—has risen by 40 percent since preindustrial times. The burning of fossil fuels like coal, oil, and gas for electricity, heat, and transportation is the primary source of human-generated emissions. A second major source is deforestation, which releases sequestered carbon into the air. It’s estimated that logging, clear-cutting, fires, and other forms of forest degradation contribute up to 20 percent of global carbon emissions. Other human activities that generate air pollution include fertilizer use (a primary source of nitrous oxide emissions), livestock production (cattle, buffalo, sheep, and goats are major methane emitters), and certain industrial processes that release fluorinated gases. Activities like agriculture and road construction can change the reflectivity of the earth’s surface, leading to local warming or cooling, too. Though our planet’s forests and oceans absorb greenhouse gases from the atmosphere through photosynthesis and other processes, these natural carbon sinks can’t keep up with our rising emissions. The resulting buildup of greenhouse gases is causing alarmingly fast warming worldwide. It’s estimated that the earth’s average temperature rose by about 1 degree Fahrenheit during the 20th century. If that doesn’t sound like much, consider this: When the last ice age ended and the northeastern United States was covered by more than 3,000 feet of ice, average temperatures were just 5 to 9 degrees cooler than they are now.
Works Cited
Ross, Rachel. “What Are the Milankovitch Cycles?” Livescience.com, 20 Feb. 2019, www.livescience.com/64813-milankovitch-cycles.html.
“What Are the Long-term Effects of Climate Change?” USGS.gov | Science for a Changing World, 2019, www.usgs.gov/faqs/what-are-long-term-effects-climate-change-1?qt-news_science_products=0#qt-news_science_products.
“Global Climate.” Encyclopedia.com | Free Online Encyclopedia, www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/global-climate.
“What is a Glacier? | National Snow and Ice Data Center.” National Snow and Ice Data Center |, 16 Mar. 2020, nsidc.org/cryosphere/glaciers/questions/what.html.
“Weathering.” Encyclopedia Britannica, www.britannica.com/science/weathering-geology.
“Weathering Processes | Physical Geography.” Lumen Learning – Simple Book Production, courses.lumenlearning.com/suny-geophysical/chapter/weathering-processes/.
“The Albedo Effect and the Reflectance of Solar Heat.” Geography and You – A Development and Environment Magazine, geographyandyou.com/reflectance-of-solar-heat/.
“Global Climate Change: What You Need to Know.” NRDC, www.nrdc.org/stories/global-climate-change-what-you-need-know.
