Two years ago I heard Stephen Schneider give a talk at a journalism seminar in Portland. He was clearly frustrated at the state of the climate debate, and was essentially dismissive of any notion that AGW wasn't true.
I think I can understand some of where he's coming from. If you read his 1990 book Global Warming: Are We Entering the Greenhouse Century? (and I recommend it, if you can find it in paperback), you'll be astonished to see how much was already known about man's influence on the climate in the 1980s -- clearly enough to even then take the subject very seriously, viz., enough knowledge to take action.
And in 20 years no action at all has been taken. Not only that, but now the entire debate has devolved into a nasty pit unlike anything ever seen in science, and all kinds of clowns and professional prevaricators have come out to openly mock honest, hard-working scientists and even threaten them (as Morano implicitedly does by publishing their email addresses). I hate to say it but you can almost look down this trend and see something truly tragic happening at some point.
I'm sure lots of scientists are frustrated. But this PNAS paper seems unnecessary. Science and scientists have done very well over the centuries by taking the high road, and while I know scientists are human and naturally express their frustration in private, it doesn't belong in a scientific journal, especially one like PNAS. You can't simply chalk up expertise based on number of publications, and who is to say what the science will ultimately be, and analyses like this one never capture all the subtleties of people's positions on a diverse, complex subject, and you just end up making things worse. Now there is one more ancillary topic to argue about instead of the science, which is the very nutrient the pro prevs exist upon.