Actually, what you tout as two points of contention are really not. The science is clear, but there are people who have their own agendas for questioning these issues.
The UN founded the IPCC. It is the authority on climate change science. They do not do science as a group on their own, they condense what science has already been done.
1. The IPCC report released in September last year answers this question with a large YES: Humanity is responsible for climate change. The probability is 95%, and that is still considered a conservative estimate.
2. The IPCC released a working draft in April of this year for the predictions on what will happen if carbon emissions continue as they do. There is a lot to read. I can sum it up for you: We would be screwed.
Even if we cut carbon emissions completely right now, the climate will still warm from the gases that are already there. Sea levels are already rising and will rise even more.
Global warming does not mean that it will be warmer everywhere, it means that the weather becomes more extreme: dry areas can expect to be more dry, wet areas will be more wet, storms are going to be stronger, etc.
As to #3, there will be a summit next year about what to do.
It is clear that carbon emissions need to be cut substantially and that there needs to be global agreements that are tough enough to do any effect.
Personally, I think the best thing would be to couple a treaty with trade: if you don't sign the treaty, those who do will add high tariffs for goods to and from your country. (And no, there is not just one economist who thought that up a few weeks ago, that idea has been debated a long time.)
In the EU, countries have had carbon allotments that could be bought and sold, but they have failed because they have been too cheap. Several countries, and the EU itself has goals for cutting emissions by certain amounts by a certain year, but there has been too little progress and it looks as if the goals won't be met if things progress as they have.
If carbon allotments are going to be highly valued and countries are going to change, then emission limits need to be tightened every year.