It is undeniable and very convincing to anyone with enough technical background to follow the scientific arguments, and no ideological biases to force a different conclusion. We know a 2 deg Celsius rise in average global temperature is enormous, but it would never be detected without a well funded program of sophisticated measurement. The data is just too noisy for it to be immediately obvious, or so it could not be explained away as differences in measurement techniques or historical archives. If you don't WANT to believe, or if you don't want anyone ELSE to believe, its easy to obscure the truth if you've got the funding. Unfortunately, the average person is much more afraid of losing his job or house or car than he is of losing his planet. Life on earth has survived massive swings in weather and climate, but they have been spread over millennia and centuries. We've never had a global civilization forced to adapt to change like that over a span of a few decades, especially when we are already approaching the max carrying capacity of the global ecosystem with a population that has doubled over my lifetime.

However, for the non-specialist, the honest (but naive) observer, the first impression is that the earth is just so big and we are so small. There are so few people on the planet, we would all fit easily into a box 2 kilometers on a side that would easily vanish if dropped anywhere in the ocean beyond the continental shelves. Sure, our agricultural and industrial activities have an impact way out of proportion to our biomass, but how many people are actually aware of how many hectares of arable land it takes to feed one human being, or how much water and energy are needed to grow our food, much less power our suburban lifestyles? And if you walk into a room with a CO2 concentration of 1000 ppm of the gas, you would feel no change in temperature or shortness of breath.

And for the first time in human history, a substantial portion of the population of earth thinks they are entitled to live like the Americans they see in our movies. Sure, if you think about it, these arguments are bogus, but its easy to see how easily they could be manipulated by those who are hoping to profit from the coming catastrophe.

Its the Tragedy of the Commons. One day you go out and see there are lily pads on your pond. The next day there are twice as many, and the next twice as many more. The weeds spread across the pond, doubling each day, but the pond is big and its mostly clear. Then one day, you notice the pond is half covered, and you've only got one more day to do something about it.

TB was right, the argument about global warming is not about science, its economic and political. It is ideological. What it will take to mitigate the damage (its too late to actually turn the problem around) is going to mean a lot of people are going to have to tighten their belts, a lot more people will never get their own single-family suburban house with 2.3 automobiles, and a very few people are not going to be able to prosper as much as they think they are entitled to because of their entrepreneurial purity and heritage. And those people just don't want to hear it. And they don't care who they have to kill to get their way.