There is a vein of septicism going around, roughly to the tune of "Science isn't done by consensus. There is a consensus on global warming. Hence, global warming must be wrong". Put as baldly as that, the argument is obvious nonsense (note, BTW, that this abandons another of the favourite septic arguments - that there is no consensus on GW. But consistency was never a strong point of the septics).
So, here is my take on it, intended to make the subtle distinctions clear:
- There *is* a consensus on global warming (see http://www.realclimate.org/index.php?p=86).
- The consensus is based around the IPCC reports which (by synthesising a vast number of scientific papers) do a fine job of outlining what is and what is not known, and carefully referencing everything back to the original papers.
- Scientifically, you cannot argue "There is a consensus: therefore...". But you *can* argue "The IPCC says such-and-such; therefore...". Because the IPCC is reporting the science; and if you disagree you can go back to the original papers and find out why.
- The argument that "Science isn't done by consensus" is irrelevant. Its close to true (I suspect that various philosophical strands would argue that the current scientific paradigm does indeed influence what research is done) but its irrelevant. Because no-one is arguing that. Science *is* done by saying: "these papers say such-and-such, therefore...".
- Sometimes, people say "but the best science is done by breaking with consensus". It certainly true that the most groundbreaking stuff is done this way - just about by definition. But that arguement *can't* be used to imply that the current consensus is wrong. Its simply a logical fallacy.
- The most obvious groundbreaking work in the 20C was relativity and QM. But in both those cases they were *not* sudden shifts from there-is-a-consensus-on-the-old-theory-everything-is-OK to spiffy-new-theory. Instead, there was a slow accumulation of results inconsistent with the old theories, and leading scientists grew more and more unhappy, and various theories were proposed to solve this. That doesn't fit GW very well - most of the GW septics are grumpy old men, not groundbreaking young scientists.
Did that help?