We hear a lot these days about what "scientists" are saying, believe, or have discovered. Especially with complicated scientific problems that have major implications for economics, politics, and society, it is important to understand the difference between scientific results and what a scientist says.
Scientists play three roles in our society, as I have written about in my book No Man's Garden: researcher, expert witness, and "priest." As a researcher, a scientist reports the results of a specific study he has done, objectively. As an expert witness, a scientist tells us about a subject in which he has worked, but generalizes beyond his own work, and gives a considered opinion based on his professional experience and best understanding. As a "priest" a scientist tells us what to think and what to believe.
Most of us scientists want to appear as the researcher, but in reality, most of the time, especially when we are dealing with complex scientific issues with broad policy implications, we function as expert witnesses. There is nothing wrong with this role, as long as we are honest in explaining that this is the role we are playing.
There is also a difference between what an individual scientist says and what a large group of scientists agree to say, when they are brought together by a political body and engaged in an attempt to reach a consensus. Most of the time, the result is "conventional wisdom" with all of its pitfalls, along with compromises that come about as the large group tries to deal with cultural and political differences. A report by such a large group is not scientific truth; it isn't even expert opinion; it's just a general negotiated agreement.