The word catastrophe usually brings to mind phenomena like tsunamis, earthquakes, mudslides, or asteroid impacts-disasters that are over in an instant and have immediately evident dire consequences. The changes in Earth's climate wrought by industrial carbon dioxide emissions do not at first glance seem to fit this mold since they take a century or more for their consequences to fully manifest. However, viewed from the perspective of geological time, human-induced climate change, known more familiarly as "global warming," is a catastrophe equal to nearly any other in our planet's history. Seen by a geologist a million years from now, the era of global warming will probably not seem as consequential as the asteroid impact that killed the dinosaurs. It will, however, appear in the geological record as an event comparable to such major events as the onset or termination of an ice age or the transition to the hot, relatively icefree climates that prevailed seventy million years ago when dinosaurs roamed the Earth. It will be all the more cataclysmic for having taken place in the span of one or a few centuries, rather than millennia or millions of years.
Humans have become a major geological force with the power to commit future millennia to practically irreversible changes in global conditions. This is what Bill McKibben refers to as "The End of Nature."1 As an example of the impact life has on global climate, the imminent global warming caused by humans does not stand out as unique or even unusually impressive. When oxygen-generating photosynthetic algae evolved between one and two-and-one-half billion years ago, they changed the composition of one-fifth of the atmosphere, poisoned much of the previous ecosystem, and more or less terminated the dominant role of methane as a greenhouse gas (oxygenation also, to be fair, set the stage for evolution of multi-celled organisms-the animals and plants we know and love). And when plants colonized land half a billion years ago, they vastly increased the rate at which atmospheric carbon dioxide is converted to limestone in the soil, leading to severe global cooling. One hardly wants to contemplate the kind of environmental impact statement that would have to be filed for either of these innovations.
What makes global warming unique in the four billion year history of the planet is that the causative agents-humans-are sentient. We can foresee the consequences of our actions, albeit imperfectly, and we have the power, if not necessarily the will, to change our behavior so as to effectuate a different future. The conjuncture of foresight and unprecedented willful power over the global future thrusts the matter onto the stage where notions of responsibility, culpability, and ethics come into play. The philosopher Hans Jonas finds in this "imperative of responsibility" a need for a fundamentally new formulation of ethics-one that takes greater cognizance of future generations and of the biosphere at large.2 It is against this backdrop that the foundation of international institutions capable of dealing with the catastrophe of global warming must be seen.
II. UNIQUE PHYSICAL ASPECTS OF THE CLIMATE CHANGE PROBLEM: IMPOSING OUR WILL ON THE NEXT 5000 GENERATIONS
In this section I will review the basic physical features that make global warming fundamentally different from all other pollution problems faced by humans. The problem of ozone destruction by chlorofluorocarbons (the "ozone hole" problem) was a small warm-up act sharing some characteristics with the global warming problem. But because the ozone hole problem was somewhat more limited in scope, and abatement of chlorofluorocarbons did not force society to confront any really difficult economic decisions, it is in a qualitatively different class. Human-induced emissions of several gases other than carbon dioxide also contribute to global warming, but in the long run, carbon dioxide is by far the biggest player and the most embedded in economic activity. …