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Global warming began 18,000 years ago as the earth started warming its way out of the Pleistocene Ice Age - a time when much of North America, Europe, and Asia lay buried beneath great sheets of glacial ice. Earths climate and the biosphere have been in constant flux, dominated by ice ages and glaciers for the past several million years. We are currently enjoying a temporary reprieve from the deep freeze. Approximately every 100,000 years Earths climate warms up temporarily. These warm periods, called interglacial periods , appear to last approximately 15,000 to 20,000 years before regressing back to a cold ice age climate. At year 18,000 and counting our current interglacial vacation from the Ice Age is much nearer its end than its beginning. Global warming during Earths current interglacial warm period has greatly altered our environment and the distribution and diversity of all life. For example: Approximately 15,000 years ago the earth had warmed sufficiently to halt the advance of glaciers, and sea levels worldwide began to rise. By 8,000 years ago the land bridge across the Bearing Strait was drowned, cutting off the migration of men and animals to North America. Since the end of the Ice Age, Earths temperature has risen approximately 16 degrees F and sea levels have risen a total of 300 feet ! Over the past 750,000 years of Earths history, Ice Ages have occurred at regular intervals, of approximately 100,000 years each. Courtesy of Illinois State Museum D uring ice ages our planet is cold, dry, and inhospitable - supporting few forests but plenty of glaciers and deserts . Like a spread of collosal bulldozers, glaciers have scraped and pulverized vast stretches of Earths surface and completely destroyed entire regional ecosystems not once, but several times.
I n the 1970s concerned environmentalists like Stephen Schneider of the National Center for Atmospheric Research in Boulder, Colorado feared a return to another ice age due to manmade atmospheric pollution blocking out the sun . Since about 1940 the global climate did in fact appear to be cooling. Then a funny thing happened- sometime in the late 1970s temperature declines slowed to a halt and ground-based recording stations during the 1980s and 1990s began reading small but steady increases in near-surface temperatures. Fears of global cooling then changed suddenly to global warming ,- the cited cause: manmade atmospheric pollution causing a runaway greenhouse effect . What does geologic history have to offer in sorting through the confusion? If ice age is used to refer to long, generally cool, intervals during which glaciers advance and retreat, we are still in one today. Our modern climate represents a very short, warm period between glacial advances. Illinois State Museum P eriods of Earth warming and cooling occur in cycles. This is well understood, as is the fact that small-scale cycles of about 40 years exist within larger-scale cycles of 400 years, which in turn exist inside still larger scale cycles of 20,000 years, and so on. Example of regional variations in surface air temperature for the last 1000 years, estimated from a variety of sources, including temperature-sensitive tree growth indices and written records of various kinds, largely from western Europe and eastern North America. Shown are changes in regional temperature in C, from the baseline value for 1900.
Courtesy of Thomas Crowley, Remembrance of Things Past: Greenhouse Lessons from the Geologic Record Earths climate was in a cool period from AD 1400 to about AD 1860, dubbed the Little Ice Age . This period was characterized by harsh winters, shorter growing seasons, and a drier climate. The decline in global temperatures was a modest 1/2 C, but the effects of this global cooling cycle were more pronounced in the higher latitudes. The Little Ice Age has been blamed for a host of human suffering including crop failures like the Irish Potato Famine and the demise of the medieval Viking colonies in Greenland. Today we enjoy global temperatures which have warmed back to levels of the so called Medieval Warm Period , which existed from approximately AD 1000 to AD 1350.
Was man really responsible for pulling the Earth out of the Little Ice Age with his industrial pollution? If so, this may be one of the greatest unheralded achievements of the Industrial Age! Unfortunately, we tend to overestimate our actual impact on the planet. In this case the magnitude of the gas emissions involved, even by the most aggressive estimates of atmospheric warming by greenhouse gases, is inadequate to account for the magnitude of temperature increases. Causes of Global Climate Change C limate change is controlled primarily by cyclical eccentricities in Earths rotation and orbit , as well as variations in the suns energy output . Greenhouse gases in Earths atmosphere also influence Earths temperature, but in a much smaller way.
Because these cycles and events overlap, sometimes compounding one another, sometimes canceling one another out, it is inaccurate to imply a statistically significant trend in climate or temperature patterns from just a few years or a few decades of data. Unfortunately, a lot of disinformation about where Earths climate is heading is being propagated by scientists who use improper statistical methods, short-term temperature trends, or faulty computer models to make analytical and anecdotal projections about the significance of man-made influences to Earths climate. During the last 100 years there have been two general cycles of warming and cooling recorded in the United States We are currently in the second warming cycle. Overall, United States temperatures show no significant warming trend over the last 100 years 1. Each year Government press releases declare the previous year to be the hottest year on record. The UNs executive summary on climate change, issued in January 2001 , insists that the 20th century was the warmest in the last millennium. The news media distribute these stories and people generally believed them to be true. However, as most climatologists know, these reports generally are founded on ground-based temperature readings, which are misleading. The more meaningful and precise orbiting satellite data for the same period which are generally not cited by the press have year after year showed no warming. Patrick Michaels has demonstrated this effect is a common problem with ground- based recording stations, many of which originally were located in predominantly rural areas, but over time have suffered background bias due to urban sprawl and the encroachment of concrete and asphalt the urban heat island effect . The result has been an upward distortion of increases in ground temperature over time2. Satellite measurements are not limited in this way, and are accurate to within 01 C. They are widely recognized by scientists as the most accurate data available. Significantly, global temperature readings from orbiting satellites show no significant warming in the 18 years they have been continuously recording and returning data 1. A Matter of Opinion H as manmade pollution in the form of carbon dioxide CO2 and other gases caused a runaway Greenhouse Effect and Global Warming?
CO2 in our atmosphere has been increasing steadily for the last 18,000 years- long before humans invented smokestacks Figure 1 . Unless you count campfires and intestinal gas, man played no role in the pre-industrial increases. As illustrated in this chart of Ice Core data from the Soviet Station Vostok in Antarctica , CO2 concentrations in earths atmosphere move with temperature. Both temperatures and CO2 have been steadily increasing for 18,000 years. Ignoring these 18,000 years of data global warming activists contend recent increases in atmospheric CO2 are unnatural and are the result of only 200 years or so of human pollution causing a runaway greenhouse effect. Incidentally, earths temperature and CO2 levels today have reached levels similar to a previous interglacial cycle of 120,000 - 140,000 years ago. This is known as the Eemian Interglacial Period and the earth returned to a full-fledged ice age immediately af...
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