I don’t think there is any real doubt that climate change is happening, or that human activity is an important cause. There is still doubt as to the nature and extent of the effects it will have. These sorts of questions are largely imponderable. This sort of change is unprecedented in recorded human history, so we cannot realistically expect to get any sort of precise idea of the likely impacts.
At this point, the debate seems to have become about what should be done. I think this move can be put down to a number of factors, including the noticeable effects climate change is already having on the environment, the widespread agreement in the scientific community, and the increasing support of public and political figures, such as Al Gore.
As far as responses go, I find it pretty odd to hear people talk about carbon credits, and restricting emissions to say, 1990 levels as solutions. These kinds of measures only serve to keep the emissions where they are now, and to redistribute who gets to do the emitting. The problem with this approach is that it is the current levels that have gotten us into this situation in the first place! Keeping levels static, or somewhat decreasing them will only serve to reduce the rate of acceleration of global warming, but cannot help to solve the problem. An incremental response to global warming is only going to work if the increments are large and frequent.
It seems to me that we need to fundamentally change the types of energy generation we use, and how we use the energy generated. To do this, we need to change the incentives involved. At the moment, oil is too cheap, because the price of it does not represent the environmental costs of using it (these costs are left to be borne by future generations, in the form of a degraded environment). One response to this would be to tax oil. This would be a good response, as it would give incentives to develop alternative energy sources. However, it risks stunting the world economy if it is not accompanied by positive measures to create alternative energy sources.
To do this, I would suggest trans-governmental “prizes” for firms which develop cost effective, clean energy sources and delivery systems.
In theory, the market will provide incentives for the development of alternative energy sources as oil becomes more scarce, and thus more costly. The problem is, I don’t think we can afford to wait that long. Effectively providing a big government incentive would lead the market to take into account the environmental and social costs of our reliance on oil, and would help to jump-start the process of finding alternatives. Basically we would be using positive incentives to correct a market failure. Coupled with gradually increasing taxes on oil, this would steer the market towards sustainable energy.