Duke,
Let me see if I can explain this. One of the things that ice cores (I'll just stick with them for this argument but there are other methods) demonstrate is the amount of CO2 that was in the atmosphere in a particular place at a particular time. Cores have now been gathered from all over the world by many different scientists. Those cores have allowed scientists to now go back in time at least 750,000 years. Longer for some areas (arctic and antarctic) and shorter for others (primarily mountain glaciers). The quantity of CO2 (as well as other gases and particulates) anywhere along the cores length can be measured, which has been done. By gathering all of that data, from all over the world, from many different scientists, we can get a pretty good idea of what has happened in that time. With me so far?
OK. The cores show that atmospheric CO2 has remained fairly stable over time but periodically we see a large spike. Why? Initially the causes were not known but today, because of other scientists in other fields, we now have a good idea. I'm sure you remember only a few years ago when Mt. St. Helens exploded in Washington State. That was, from a geologic perspective, a small explosion. But that event can be precisely dated. As can eruptions from volcanoes around the world that are within human memory (Pompeii, Pinatubo, etc.) Those eruptions leave a distinct marker in the glacial record which we can now, but not 20 or 40 years ago, identify. Still with me?
OK. We now have a baseline of atmospheric CO2 for many years. But starting about the 1850's, a curious thing is seen. CO2 starts increasing at a rate that cannot be explained by natural occurances. Why? After looking at all of the different possibilities of why, the cause became clear. At that time man started building smokestacks. Smokestacks allow for escaping gases and particulates to reach portions of the atmosphere that, previously, could not be attained. As time goes on we add other things to the smokestacks: cars, tractors, trucks, etc. etc. Are we OK so far?
OK. All of these gases and particulates eventually fall back to earth and some of them fall onto glaciers and ice sheets where they are trapped, buried and become part of the atmospheric record. That record is what scientists are reading today. And that record is what allows scientists to define a particular date.
The "climate" was not changed in the 1850's. What was changed was the CO2 concentration, it began rising at a rate that could not be explained by natural processes. And what is worrisome to scientists (and now the Pentagon) is that CO2 concentrations are continuing to rise at a rate that "will" have effects on key natural (and man made) processes, such as the Atlantic Conveyor (there is a fairly good explanation of these in the Pentagon article).
As far as I know, CO2 has never been at 0 and never will be, it is natural for it to be in the environment at certain levels. The problem is that the concentrations of CO2 are increasing and that we can clearly now demonstrate where the concentrations are coming from, mans activities. This has now been demonstrated by experiments in the lab and computer programs that scientists from around the world can replicate. One thing you should remember about science is that just because a single scientist says something, that doesn't mean it is so. But when a whole lot of scientists from around the world start saying the same thing, then you had better listen.
" from zilch to change during the industrial revolution. <---IS THIS CORRECT?"
I hope that part of your question is answered.
"would you not expect the climate change to be more extreme in the current day 150 years later?"
No, not really. This is a gradual process, but accelerating. 150 years ago was the start of the industrial revolution. There were only a few industries with smokestack capabilities. Over time that increased to the point where virtually all of us that drive a car are contributing to the problem. Now, China (and other portions of the world) are modernizing and also contributing to the problem. The things you speak of,
"then shouldn't we be wearing protective gear"
will happen to successive generations unless we start to do something about it now. But protective gear is not really the main problem (you're thinking of increased UV radiation, which is related). The direct effects of global warming are much more problematic (read the Pentagon article for a very good explanation). Just a few: war, pestilence, disease, famine (sound familiar)?
Hope this helps and explains a few things. Let me know if this doesn't make sense.
