What does geologic history have to offer in sorting through the confusion? Quite a bit, actually.
"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
Periods 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. Compiled by R. S. Bradley and J. A. Eddy based on J. T. Houghton et al., Climate Change: The IPCC Assessment, Cambridge UniversityPress, Cambridge, 1990 and published in EarthQuest, vol 5, no 1, 1991. Courtesy of Thomas Crowley, Remembrance of Things Past: Greenhouse Lessons from the Geologic Record
Earth's climate was in a cool period from A.D. 1400 to about A.D. 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 A.D. 1000 to A.D. 1350.
"...the Earth was evidently coming out of a relatively cold period in the 1800s so that warming in the past century may be part of this natural recovery."
Dr. John R. Christy
(leading climate and atmospheric science expert- U. of Alabama in Huntsville)
Global warming alarmists maintain that global temperatures have increased since about A.D. 1860 to the present as the result of the so-called "Industrial Revolution,"-- caused by releases of large amounts of greenhouse gases (principally carbon dioxide) from manmade sources into the atmosphere causing a runaway "Greenhouse Effect."
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. So what causes the up and down cycles of global climate change?
Causes of Global Climate Change
Climate change is controlled primarily by cyclical eccentricities in Earth's rotation and orbit, as well as variations in the sun's energy output.
"Greenhouse gases" in Earth's atmosphere also influence Earth's temperature, but in a much smaller way. Human additions to total greenhouse gases play a still smaller role, contributing about 0.2% - 0.3% to Earth's greenhouse effect.
Major Causes of Global Temperature Shifts
(1) Astronomical Causes
11 year and 206 year cycles: Cycles of solar variability (sunspot activity)
21,000 year cycle: Earth's combined tilt and elliptical orbit around the Sun ( precession of the equinoxes)
41,000 year cycle: Cycle of the +/- 1.5° wobble in Earth's orbit (tilt)
100,000 year cycle: Variations in the shape of Earth's elliptical orbit (cycle of eccentricity)
(2) Atmospheric Causes
Heat retention: Due to atmospheric gases, mostly gaseous water vapor (not droplets), also carbon dioxide, methane, and a few other miscellaneous gases-the "greenhouse effect"
Solar reflectivity: Due to white clouds, volcanic dust, polar ice caps
(3) Tectonic Causes
Landmass distribution: Shifting continents (continental drift) causing changes in circulatory patterns of ocean currents. It seems that whenever there is a large land mass at one of the Earth's poles, either the north pole or south pole, there are ice ages.
Undersea ridge activity: "Sea floor spreading" (associated with continental drift) causing variations in ocean displacement.
For more details see:
http://www.ngdc.noaa.gov/paleo/milankovitch.html
http://www.abc.net.au/science/news/e...ish_233658.htm
Playing with Numbers
Global climate and temperature cycles are the result of a complex interplay between a variety of causes. 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 Earth's 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 Earth's climate.
During the last 100 years there have been two general cycles of warming and cooling recorded in the U.S. We are currently in the second warming cycle. Overall, U.S. temperatures show no significant warming trend over the last 100 years. This has been well established but not well publicized.
Each year Government press releases declare the previous year to be the "hottest year on record." The UN's 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 little or no warming.
Dr. 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 time. Satellite measurements are not limited in this way, and are accurate to within 0.1° 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.
A Matter of Opinion
Has manmade pollution in the form of carbon dioxide (CO2) and other gases caused a runaway Greenhouse Effect and Global Warming?
Before joining the mantra, consider the following:
CO2 in our atmosphere has been increasing steadily for the last 18,000 years-long before humans invented smokestacks. Unless you count campfires and intestinal gas, man played no role in the pre-industrial increases.
CO2 concentrations in earth's 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, earth's temperature and CO2 levels today have reached levels similar to a previous interglacial cycle of 120,000 - 140,000 years ago. From beginning to end this cycle lasted about 20,000 years. This is known as the Eemian Interglacial Period and the earth returned to a full-fledged ice age immediately afterward.
Total human contributions to greenhouse gases account for only about 0.28%of the "greenhouse effect". Anthropogenic (man-made) carbon dioxide (CO2) comprises about 0.117% of this total, and man-made sources of other gases (methane, nitrous oxide (NOX), other misc. gases) contributes another 0.163% .
Approximately 99.72% of the "greenhouse effect" is due to natural causes -- mostly water vapor and traces of other gases, which we can do nothing at all about. Eliminating human activity altogether would have little impact on climate change.
If global warming is caused by CO2 in the atmosphere then does CO2 also cause increased sun activity too?
Put another way, rising Earth temperatures and increasing CO2 may be "effects" and our own sun the "cause".
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