Global Warming

I've been reading some discussions on Global Warming lately on a website I check almost daily, the Stormtrack.org forums. I've not posted anything there, because the site is for storm chasers, and I'm mostly a wannabe. I suspect that my opinions would not be highly regarded, and so they would probably not add much to the discussion.

I am a skeptic. I not only have doubts about anthropogenic GW, but GW itself. I admit I have not looked into the research behind GW claims, so I classify myself as a doubter more than a denier.

GW proponents claim they have the numbers to show that worldwide average temperatures have risen. My question is, where did those numbers come from? In the few college-level science courses I have taken, the validity of numbers from measurements depend on the accuracy of the instrument used, and any envrionmental factors that could affect the measurement. Are the thermometers of 100 years ago as accurate as the ones we use today? The placement of those thermomters could also be an issue. Before WW2, in the US, themometers for the Weather Bureau (now the NWS) were placed in downtown areas where the Bureau offices were. As the use of radar spread, NWS offices moved to airports where the radars where. With the modernization of the NWS, Automated Surface Observation System (ASOS) stations were placed at airports near the ends of runways. Sure the sensors are now placed in areas away from heat-retaining buildings, but they are now exposed to jet exhaust. Have these GW studies accounted for these changes?

In Introductory Meteorology, I learned that the earth's heat budget is always balanced, unlike our federal budget. All the heat that enters our atmosphere eventually leaves by radiating out into space. Greenhouse gases are said to retain heat, so the questions that come to my mind are these: How long do the gases "hold on" to the heat? What will happen because of this reatined heat? How much heat is retained?

Another thing I learned in Intro Meteorol. is the compostion of the atmosphere is a known mixture of gases of known porportion. If man is adding carbon dioxide to the atmosphere, are we changing the compostion of the atmosphere? Is it enough to account the amount of warming claimed?
Combustion of fossil fuels not only produces carbon dioxide, but water vapor as well. Water vapor is also a greenhouse gas. Do the climate models account for water vapor? Have humidity values gone up?

Averages are statistics. We hear of scientists conducting studies that produce the GW claims, but have statisticians reviewed the math?

I suppose I shall have to look at these studies for myself to find the answers to these questions.