The environmental impact of industrialization is the primary cause of earth's current warming trend.

We agree that global warming is a cyclical phenomenon, but we disagree about its causes. That seems like a reasonable debate. In your previous argument you assert that "the ice back in the Ice Age was not melted down because the cavemen were driving cars or emitting harmful toxins into the air." I completely agree with this. A hunter/gatherer lifestyle has the least environmental impact of any human lifestyle. I'm not saying that prehistoric man was the source of an abnormal increase in levels of Carbon Dioxide in earth's atmosphere. In fact, your suggestion that prehistoric man had no way to influence the level of CO2 in his atmosphere supports my argument that the level of CO2 observed in ice core samples was totally natural, making these samples ideal data by which to examine the variation in CO2 caused by modern man. The method by which most of earth's warming occurs is the greenhouse effect. This effect is closely related to the level of certain gases like CO2 in earth's atmosphere. This scientific fact was discovered by Joseph Fourier in 1824, and is supported by the EPA, NOAA, NASA, and the IPCC. http://www.epa.gov... http://www.oar.noaa.gov... http://liftoff.msfc.nasa.gov... http://www.ipcc.ch... The basic concept behind the greenhouse effect is that: "Earth's atmosphere acts like a greenhouse, warming our planet in much the same way that an ordinary greenhouse warms the air inside its glass walls. Like glass, the gases in the atmosphere let in light yet prevent heat from escaping." (http://liftoff.msfc.nasa.gov...) CO2 is one such gas. So long as CO2 is present in the atmosphere it will reflect infrared radiation back to earth, causing the greenhouse effect. More CO2 in earth's atmosphere means even more reflected infrared. In recent history, there have been no abnormal natural releases of CO2 or any other greenhouse gas in a level great enough to significantly effect global climate. The current natural factors that contribute to greenhouse gas emission and reduction are the same as they were 400,000 years ago. Ice core data has shown that when natural causes were the only determining factor, the highest level of CO2 that ever occurred was 300ppmv (http://www.cnrs.fr...). The level of CO2 in the atmosphere as of 2004 was 377ppmv and rising. Direct atmospheric CO2 measurements are possible, and have been conducted by researchers at the Mauna Loa Carbon Dioxide observation station since 1959. In the first year of is operation, Mauna Loa found the atmospheric CO2 content to be at a level of 315.98ppmv. In 2004 the station found earth's atmospheric CO2 content to be 377.38ppmv. An increase this drastic is unprecedented historically, and thus can not be attributed to natural causes. Here's a graph illustrating my point: http://en.wikipedia.org... Natural causes have been shown to have an effect on the earth's climate, but these variations stay within the range of 180ppmv to 300ppmv as shown by ice core data. Because the only new sources of CO2 emission are related to human activities, those activities are the sole cause of the abnormal increase in CO2 levels observed by the Mauna Loa station.