For the record, I'm skeptical of the whole premise of the (non-)event. But, since 9000 other bloggers are holding forth, there's little harm in adding one more voice to the din.
Climate change is in large measure a problem of scalar mismatch : activities at the local scale of households and neighborhoods have spillover effects at much larger scales, which in turn change the configuration of opportunities and constraints at the local scale. With this come both problems of perception and problems of legitimacy.
On the problem of perception, I put it this way in a paper published in 2007, called "A Little Knowledge of Dangerous Things":
First, the effects of climate change are dispersed in time. Climate is not weather: I cannot look out the window and tell you what the climate is. Rather, climate can only be perceived, if at all, over a long period of time as that which binds the weather together in a given place, or over the surface of the Earth as a whole; it might be described as the cyclical style or mood of the weather, or as the habitual relation of weather to the seasons. If there is a permanent change in the climate, then it will be visible to us, if at all, as a kind of background radiation that pervades the whole of the visible. The effects of a change in global climate would be more directly perceptible, but they would be scattered through an array of events - a flood, a dry spell, a storm - that are not connected together in a way that is obvious on the face of things. If I am content simply too observe the weather, I might eventually come to grasp that the mood of things has changed, but perhaps only vaguely, and perhaps with a sense that the mood might yet change back. To connect such events together in a systematic way, and to grasp that the change in climate is accelerating and irreversible, requires something other than unaided perception.I go on in that paper to talk about some of the difficulties of bringing scientific knowledge into ordinary perception and understanding of the world. The question is: Is it possible to really feel "in my bones", to see in this particular place, the theoretical connection from local action to global consequence and back to some vague future constraints on local action? If it's possible - and if it would help in making better decisions - how do I bring this about?
Much the same can be said of the physical and chemical causes of climate change, the second dimension along which the threat is dispersed. Here the difficulty is to relate human activities that are not otherwise connected, from flipping on a light switch to raising cattle. The challenge of grasping the threat theoretically, then, is to connect together my actions now with diverse and often subtle changes in observable weather patterns years or even decades from now. The connection between them passes out of sight, into the depths of the world. In effect, climate researchers claim to peer into the invisible depths of the world, to espy the hidden order of real objects that explains the shifting and apparently disconnected fragments of our lived experience.
The problem of scalar mismatch also plays out in the question of how, if at all, we may legitimately coordinate action in response to the threat of global climate change. Here again, there is a global process to which I as an individual have very little direct connection. I voted last year in the election that brought in a new American administration, which will in turn appoint delegates who will travel to Copenhagen in December for a new round of negotiations that may result in an international agreement on climate change. Whether they succeed or not, what happens at the COP-15 will likely have some effect on the contours of opportunity and constraint in my local place.
It seems appropriate to address a global problem on a global scale, even if it is a global problem with roots in lots of particular places. Climate change does begin at home, with the choices each of us makes as citizens and as consumers, but it begins in everyone's home. It's what economist colleagues of mine call a collective action problem.
The question is whether a global agreement can really have political legitimacy along the lines of democratic theory: your consent and mine seems almost beside the point, and the delegates to COP-15 are our "representatives" in only the most abstract sense of that term. Yet we will be bound by any agreement they reach or, perhaps, harmed by their failure to reach an agreement.
How, then, can the process be made more legitimate? How can it be made more responsive and accountable to the governed?
There have been some experiments along these lines. Blog Action Day is supposed to be one, though, as noted above, I have doubts about its usefulness. The World Wide Views project is another, one I think much more promising. Still, the questions remain open.
 The Ethics of Metropolitan Growth, p.123.
 Robert Kirkman, "A Little Knowledge of Dangerous Things: Human Vulnerability in a Changing Climate" in Suzanne L. Cataldi and William S. Hamrick, eds, Merleau-Ponty and Environmental Philosophy: Dwelling on the Landscapes of Thought, Albany: SUNY Press, 2007, p.27