"The problem with this whole debate is that even the scientists disagree with each other.  One group uses a computer model to predict a 5 deg warming trend and another group uses the same model to predict a 5 deg cooling trend."

Long-term climactic models are notoriously unreliable.  That is why I did not bother bringing them up.  I was talking about observations that are on record and peer-reviewed.  But you are right, although it has been warming up, any talk of a trend implies prediction.

"In the United States, 50% of all-time state record highs were set in the 1930s, before industrialization was widespread."

Yes, the dustbowl.  States are localized records, and only half of them support your point.  Temperatures fluctuate quite a bit over distance.

"1999 was the warmest year on record globally. (100 years of data is less than a drop in the bucket)"

This is not true, according to NASA that title goes to 1990:

http://library.thinkquest.org/26026/Statistics/the_ten_warmest_years_from_188.html?tqskip1=1&tqtime=0307

Only the table at the top is important.  All of the 10 hottest years on record are since 1973.  It's a drop in the bucket, but it happens to be the most recent drop in the bucket.  Global temperatures have risen recently.

"Throughout natural history, overall temperatures have swung as much as 10 deg or more in one decade."

How often are decades of change in one direction adjacent?  Some of those 1-decade changes occurred as part of longer-term, greater trends, such as the beginning or end of an ice age.  I would like to see the source, it sounds interesting.

"Although the Earth's surface temperature is warming, weather balloons and satellites don't show any warming in the lower atmosphere over the last two decades."

What is your source for this?

Let's assume everything you posted is true.  None of it contradicts my post, it is mostly supplemental information: computer predictions, state records, and one-decade temperature trends throughout natural history.  The atmosphere temp is interesting, I had not heard that.  I would like to know more.

Many sources that I consider to be reliable, or at least impartial (NASA, World Meteorological Organization, academia), have reported that overall, the earth has been warmer recently than it was farther back in the recorded history of temperature.  Many of those same sources report a sharp increase in measurable levels of greenhouse gases.  I also consider the mechanism by which greenhouse gases work to be well-explained and well-proven.  After all, the earth has not frozen solid.

Even if we suppose that we are not responsible for the changes in either the temperature or the gas levels, we know that a) we do produce greenhouse gases, and b) we will be harmed if the temperature of the earth continues to rise.  While significantly lowering our greenhouse gas production would be an economic burden, it's my opinion that overall it would less of a burden than would result from a hotter earth.  In fact, I believe lowering our gas output would have tangible economic benefits as well, such as the creation and stimulation of new industries, and an increase in air quality.  I think it's the conservative and responsible course of action, the one that prepares for a problem a lot of smart people think is coming.  It they are all wrong, hey, we'll still have cool future-cars and cleaner air anyway.