Global Catastrophe
Michael Crichton, the science-thriller author, has had his share of abuse since he infamously came out as a skeptic of global warming a few years ago. I haven't paid much attention to the kerfuffle (I never took him that seriously as an expert on scientific matters to begin with), but I ran across a presentation he gave on complexity and the environment a few months ago.
I find that, despite the fact that I don't take him seriously as a scientist, he makes a strong case for a couple of points:
Humans have a long and remarkable history of predicting imminent global catastrophe (he doesn't go back that far, but I know of predictions dating back to the middle ages), none of which have turned out to be true in retrospect. Therefore, we should treat all such claims (including, by implication, the more extreme predictions relating to climate change) with a huge amount of skepticism.
We really don't understand in any meaningful sense how extremely complex systems like global climate react to artificial changes (except, perhaps, in the most extreme and/or general cases).
I agree with both of these points (even before reading his article), though I don't agree with the implied conclusion that we shouldn't worry about the effect of increasing carbon dioxide in the atmosphere. As a general rule, I think we should tread lightly when it comes to making big changes in things we don't really understand.
On the first point, the simple fact that life continues to exist on Earth, despite billions of years of every kind of abuse the solar system can throw at us is very strong evidence that, rather than being fragile, our planet's overall climate is actually extremely robust. Sure, there have been times when many species died out at once because of climate change, but those events can be counted on the fingers of one hand despite billions of years of history, and they appear to have been triggered by truly cataclysmic events like giant meteor impacts. Events far greater than anything humans are even capable of producing at this stage in our development. Yet life continues.
On the second point, it is true that there are very sophisticated computer models, but even the best model makes absurd simplifications, and there are big swaths of knowledge about climate dynamics which are still completely unknown. We do not know the effect that these as-yet-unknown factors will have on the climate. For example, just in the past week there have been news reports that the glaciers in Greenland appear to be melting far faster than predicted by anyone's models. This trend, if it continues, will have a significant impact on global sea levels and the climate of Europe. Yet we do not yet understand why it is happening, what might accelerate the trend, or what might make it stop or reverse (though there are already lots of theories).
My own opinions on global warming run more-or-less as follows:
It is indisputable that atmospheric levels of carbon dioxide are climbing as a direct effect of human activity. We should, as responsible citizens, work to mitigate this change in an expeditious but deliberative (not panicked) manner.
It is almost certain that, as a direct result of the increase in CO2 levels, the average global temperature is increasing and will continue to increase. Even if we could somehow end all CO2 emissions tomorrow, it is probably too late to stop a meaningful change.
As anyone who lives in Minnesota knows from experience, the "average temperature" is the mythical midpoint between extremes of hot and cold. Just because the global average temperature is increasing does not imply that any given spot will get warmer. Some places will get warmer, and other places will get colder. Some places will get drier, and others wetter. Our current understanding of climate dynamics can't make any but the crudest predictions about local or regional climate changes.
The more alarmist predictions of social breakdown, chaos, dogs and cats living together, etc. are bogus. There is likely to be displacement, hardship, and significant economic harm to some groups of people, but nothing worse than the run-of-the-mill volcanoes, earthquakes, and other natural disasters we already deal with regularly (for example, a quarter of a million killed in an earthquake/tsunami--a disaster unrelated to global warming, yet something of this magnitude happens every couple hundred years or so).
Some major cities may have to be abandoned because of rising sea levels. Yet the experience of Hurricane Katrina shows that even the near-abandonment of New Orleans is something we can deal with without collapsing the fabric of our society (aside from the affected city itself). The city is unlikely to have even half its former population any time in the near future, and if New Orleans is hit by another major hurricane in the next few years it will almost certainly be permanently abandoned or nearly so. Yet people's lives will go on with out much disruption most everywhere else: it would be a disaster, but not a disaster of such magnitude that life and society as we know it would end. We will deal, as we always do.
So to summarize, I think we have already done a lot of whatever damage we're likely to do. While we should take steps to reverse what we've already done, the fact of the matter is that we're simply going to have to cope with the changes. But I don't see the changes as anything more than what civilizations have had to deal with in the past. The planet is littered with Great Cities which are abandoned or mere shadows of their former selves (plus a couple which got blown to smithereens in volcanic eruptions). Adding a few more to the list over the next couple hundred years just isn't that unusual when you look at it from the perspective of 6,000 years of human civilization.
I don't know if this makes me an optimist, a pessimist, a realist, or a skeptic on global warming (maybe it makes me a Buddhist: we're going to get what we deserve, and we'll just have to make the most of it). But I think its a much more balanced and reasonable attitude than the overheated rhetoric I've been hearing from both sides lately.