Dr. Holdren is certainly entitled to his views, but what concerns me is his tendency to conflate the science of climate change with prescriptions to cut greenhouse emissions. Even if most climate scientists agree on the anthropogenic causes of global warming, that doesn’t imply that the best way to deal with the problem is through drastic cuts in greenhouse emissions.
There is some merit on Tierney's criticism, but it is obviously the reverse of what's really happening. Whenever I have talked to a scientifically literate person who accepts the AGW consensus, and I have challenged it, it is never more than a couple of minutes before they something like "well, maybe there is room for doubt, but the things we should do about global warming are all things we should be doing anyway, like reducing fossil fuel use".
It's fair enough to believe both of those things, but each proposition needs to stand on its own without support from the other. Both sides of the debate have a tendency to shift ground when presented with strong arguments - do point me back here if you catch me doing it.