In the policy debate over global warming, anti-AGW advocates often disparage "consensus" as a refuge for scoundrels and bad science. However, my experience is that consensus is in reality the cornerstone of science.
Science is a multi-layered, collective, and impersonal process consisting of three parts. First is the individual scientist testing hypotheses according to the norms of his or her field. Second, the results of the individual scientist undergo peer-review and are published for the community to evaluate. At this point a result may be considered preliminary, but not proven. Third, important claims are then re-tested in the "crucible of science" -- they are either reproduced by independent scientific groups or they have their implications tested to insure consistency with the existing body of scientific knowledge. After enough tests/reproductions, a CONSENUS emerges that the idea is correct.
In the end, claims that are repeatedly verified by the scientific community (e.g., the Earth is warming, DNA is a double-helix, CFCs destroy ozone) eventually come to be accepted as true.
A good example is Einstein and his theory of general relativity. When he published his theory, it was not immediately accepted. However, it was rigorously tested by other scientists, most famously by Eddington's observations of star positions during eclipses, and eventually it was accepted as being "true" by the community. In other words, a consensus emerged that it was correct. At that point, people moved on to the next question, using Einstein's theory as a building block to the next interesting scientific question.
The key point here is the importance of consensus. After an idea is sufficiently well tested, everyone simply accepts the idea and people move on. While a scientific consensus might turn out to be wrong, for important and well-tested ideas (e.g., smoking causes cancer, the Earth is warming), it's exceedingly unlikely.