In a recent Guardian interview by Leo Hickman, Al Gore spelled out why he thinks good things will come of the UN climate conference in Copenhagen this year:

Barrack Obama's election is] one of the main factors. We have a big ally in reality. The planet is under assault. This collision with human civilisation, as it’s currently being operated, is increasingly dire. An economist called Herman Daly said years ago that we're operating Planet Earth as if it's a business in liquidation. More and more people are recognising that. And one of the political tipping points came in the US election last November and the decision by President Obama to keep his campaign pledges and to move boldly and swiftly towards a cap-and-trade system, and incentives for renewable energy, a national smart grid, and all the other things he is proposing. I think that movement, once begun, will shift the world system towards a new equilibrium. In the US, there have been 80 cancellations of major new coal-burning plants and people thought that maybe we'll be able to block a few of them, but they have now virtually stopped building them in the US.

[Business leaders] are seeing the writing on every wall they look at. They're seeing the complete disappearance of the polar ice caps right before their eyes in just a few years. They're seeing the statements of Chinese leaders as they're instructing their provinces to come up with quotas for a cap-and-trade option internally. They're seeing the new US administration. They're seeing Gordon Brown and David Cameron both advocate dramatic changes here [in the UK]. In the US, they're seeing the Environmental Protection Agency going to regulate CO2 as a pollutant. Just yesterday they put out a request for a carbon registry where large firms have to publicly account for their CO2 emissions. And they're looking at Washington DC where, two weeks ago, there were 12,000 young people in town [marching] on this issue and 2,000 of them formed a barricade around the coal plant…

If you look on a global basis, the largest grassroots movement in the history of the world is emerging. There are many hundreds of thousands of new organisations that have sprung up all over the world and, 20,000 here and 20,000 there, when you add it up globally, it's a big movement.

There’s also a nice piece about what he thinks of nuclear below:

 http://www.guardian.co.uk/environment/blog/2009/mar/16/climate-change-al-gore