Keep in mind that I am not someone who is happy about Global Warming. I'm not thinking that it will teach the bad naughty Western Civilizations to love and cuddle their Mother Earth. I don't have anything to gain by Global Warming happening. I just have a fair amount of education (degree in Environmental Science and active study since 1992) in the area and know more about it than most (not all).
It is true that no one is 100% sure as to exactly how Global Warming would work. There are too many variables to be able to account for them all. Remember, Doctors almost never really know exactly what is wrong with you. 9 times out of 10 they are taking an educated guess. Even so, it takes a fairly dim person to ignore a doctors diagnosis simply because they are 100% positive. We do have pretty good odds given to us by the people who know this stuff (almost all of them smarter than almost all of us AND have spent a lot more time checking the problem out). What we do have is a pretty good understanding of what things account for the cycles that maintain the environment that we live it. Scientists (the same ones that have nothing to gain from Global Warming and really know the topic well) have been able to do studies on the atmospheric conditions of the past and also back-track to get pretty close to figuring out what we put in the atmosphere and where it goes. Their figures pretty much account for what is going on, especially for the rise in Global CO2, Methane, et al. and the rate at which people have been dumping it into the air. If it was an impending Ice Age there would be a large discrepancy in the calculations, of which there isn't. What are the chances that an Ice Age just so happens to be coming at just the right time and rate to co-inside with these people's calculations AND that the CO2 greenhouse gases we have been pumping out are magically disappearing? Fairly slim. Lots of people have the Rush Limbaugh approach. They learn a little bit from other people who don't want it to happen and pick and choose what facts paint the picture they way they want it to be. I understand wanting things to work that way, but they just don't. They tend to say "well look, the average temp. has only risen an average of one degree over the last X-number of years (different people quote the stat differently). For one thing that is a global average. If you have winters that are 9 degrees cooler and summers that are 10 degrees hotter, then you have a one degree increase, and that doesn't even cover the regionally warming and cooling. If the grain belt of the United States raises only a few degrees (projected) and Europe cools a few degrees (also projected) then it isn't just nicer in South Dakota in January. You have the agricultural center of the world no longer with the proper climate to support the farming necessary. So what? It shifts north into Canada and we farm there, right? No. Top soil North of the grain belt is not able to support the intensive agriculture that would be needed. over half of the World's cereals would no longer be able to be grown. They also ignore the fact that the usage of the things that are responsible for Global Warming is increasing exponentially. Thus, things will get much worse much more quickly than in the past. They also ignore the positive and negative feedback loops that will exacerbates the problem (disruptions in the Thermalhaline Cycle due to the reduction in salinity of the Atlantic Ocean will slow or halt the nutrient dispersal system that allows the coccoliths to flourish. Coccoliths are one of the primary ways that CO2 is stripped from the atmosphere.) Thus increasing the rate at which CO2 builds up in the atmosphere. And that is just one of many loops that will make things worse once the critical threshold is reached. It is just like moving your hand towards a lit candle. Everything is fine for a long time, but once you cross a certain boundary you have a problem. The big problem with waiting until allthe evidence is in is that it will be to late. It is sort of like not being sure that jumping off a bridge will kill you until you hit the ground. You might survive, but why not re-think jumping in the first palce and take the stairs? Just a little rationality and some extra time for technological advances will go a long way.
I'm not sure why I am writing this. Those that refuse to learn about the problem and just want to ignore it aren't going to read it anyway.