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:

Playing with Numbers

G lobal 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. temperaturesshow no significant warming trend over the last 100 years (1). 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(2). 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 (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?
Before joining the mantra, consider the following:

Compiled by R.S. Bradley and J.A. Eddy based on J.T. Houghton et al., Climate Change: The IPCC Assessment, Cambridge University Press, Cambridge, 1990 and published in EarthQuest, vo. 1, 1991. Courtesy of Thomas Crowley, Remembrance of Things Past: Greenhouse Lessons from the Geologic Record 1. The idea that man-made pollution is responsible for global warming is not supported by historical fact. The period known as the Holocene Maximum is a good example-- so-named because it was the hottest period in human history. The interesting thing is this period occurred approximately 7500 to 4000 years B.P. (before present)-- long before human's invented industrial pollution.
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Figure 1
2. 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 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.

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Figure 2
3. Total human contributions to greenhouse gases account for only about 0.28% of the "greenhouse effect" (Figure 2). 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.

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Figure 3
4. If global warming is caused by CO2 in the atmosphere then does CO2 also cause increased sun activity too?
This chart adapted after Nigel Calder (6) illustrates that variations insun activity are generally proportional to both variations in atmospheric CO2and atmospheric temperature (Figure 3).
Put another way, rising Earth temperatures and increasing CO2 may be "effects" and our own sun the "cause".
"We have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we may have. Each of us has to decide what the right balance is between being effective and being honest."

Stephen Schneider (leading advocate of the global warming theory)
(in interview for Discover magazine, Oct 1989)http://www.clearlight.com/~mhieb/WVF.../ice_ages.html