I would agree that climate change is not fully understood and the ozone layer is not fully understood. But I personally believe that both are legitimate problems caused by human activity.

I think the ozone depletion was something that no one expected when we started releaseing so many CFCs into the atmosphere years ago, and it is a disaster that was just narrowly averted. Ozone depletion was not an obvious consequence of using CFCs, and the role of the ozone layer in protecting us was not fully appreciated. Once we realized that we were depleting the ozone layer and that the ozone layer was important, we took action to stop damaging it. I think that one nearly got past us, and we were lucky to figure it out in time to do something about it. I think you don't hear very much about it now, because the problem is considered to be "solved." I would not conclude that we don't hear about it now bacuse it never was a legitimate problem.

Climate change is definitely not fully understood. Some of it is certainly due to non-human factors such as natural fluctuation in CO2 levels, variations in the earth's orbit and angle, changes in the output of the sun, and probably other things that we do not understand.

But I do not think you can discount the fact that human activity has changed the composition of the atmosphere. All of that carbon was under ground and we have dug it out, burned it, and put it into the air. The processes that took it out of the air in the first place and put it undersground in the form of fossil fuels took many millions of years, and we have reversed that process in a hundred years or so. It's a very rapid rate of change to a system we do not fully understand, so it seems like a dangersous thing to do. There is a lot of evidence that in the geologic past, periods of higher temperature climate corresponded to periods of higher CO2. So there is a lot of evidence to suggest that chaniging the CO2 content of the atmosphere could change the climate. Even if the evidence is not conclusive, you have to wonder how much we should be willing to gamble.

One of the factors that comes into play when you talk about changes to complex systems is the idea of equilibrium and the resiliency of the status quo. Complex systems like the climate have thousands of inputs and feedback loops that keep the system in relative equilibrium, with minor variations. So maybe adding some CO2 would encourage plant growth that would pull that CO2 back out of the air and restore equilibrium. Or maybe a small increase in temperature might somehow change the pattern of cloud cover, and reflect more heat away into space, and restore the equilibrium. But in many complex systems, if you apply a large enough or constant enough new input into the system, the system will suddenly fall into a new and different equilibrium. Often the system goes through a period of chaotic change before it finds it's new equilibirum. Sometimes it remains in a chaotic state and never finds a new equilibrium.

My fear would be that the climate and systems dependent on climate, such as natural ecologies and agriculture, would change suddenly into a new equilibrium. Even worse than a new equilibrium would be a period of chaotic climate fluctuation. I'm not really worried that the planet would experience a runaway climatic disaster and become as hot as venus. I'm more worried that we could experinece several years of crazy weather that would cause massive worldwide crop failure and begin a cascade of famine and war. Our population is so high, so well armed, and so interdependent, that I think a disruption in food supply could trigger a collapse of our society.

If you move beyond the question of climate change, there are a lot of other human activities that cannot be sustained at current levels. There are many historical examples of different societies that collapsed because intensive agricultural techniques destroyed the long term sustainabity of their crop land. Generally it is belived that these collapses occurred suddenly with very little warning.

Regarding your last point about people motivated by greed and power --- well, I agree that people in power often use fear to get what they want. But most of my experience with poeple invloved in environmental debate has not led me to believe that people concerned about the environemnt are seeking power. Maybe some are, but not most. It seems to me like it is more common that people who resist changes designed to protect the environment are motivated by their own vested interest in the status quo. So it is important to look at the details of both sides of the debate.