You want proof as if we (humans) only move forward when absolute proof is available. Did Colombus have proof or just a preponderance of best available evidence that the earth was round? There are precious few examples in science or engineering where absolute incontrovertible proof is available before people act. Certainly in medicine there is rarely proof, just best available evidence to guide decision making. If I wait until there is absolute proof that a patient has laboratory confirmed sepsis before starting therapy rather than beginning antibiotics when a preponderance of clinical evidence points to the possibility or likelihood of infection, that would be malpractice. I see the climate debate in similar terms. If a preponderance of evidence supports AGW, then act on it and revise as necessary as new data becomes available. With a system as complex as the global climate there is unlikely to ever be a predictive model that is precisely accurate. That doesn't mean we are paralyzed though. If the preponderance of evidence points to CO2 as important in climate change and the human contribution to atmospheric CO2 can be mitigated, then why sit on our hands?
There is always room for reasonable skepticism in scientific endeavors but there is a big difference between reasonable skepticism and obstructionism motivated primarily by political agendas. The "denier" blogs that are so frequently referred to as sources of information by skeptics in this thread are nearly all blatantly political rather than scientific. I have stumbled upon some British skeptic blogs (eg Bishop Hill) which are far more rooted in science and seem to be counterparts to the skeptical science website rather than BWAAHAHA commie conspiracy baloney. However, even Bishop Hill doesn't provide substantive criticism of the IPCC summaries of evidence and focuses, at least based on my first reading, on pointing out rather trivial mistakes in graphs and arithmetic rather than providing a credible alternative hypothesis. Like it's conclusions or not, the IPCC summaries reflect current consensus opinion of those who are best able and prepared to interpret climate data. It seems rather foolish to ignore such a report just because you don't like the consequences.