Hal Lewis is not a "leading scientist." Maybe 35 or 40 years ago he might have ranked at the second tier, but certainly not in the field of atmospheric science, where he is essentially a nobody. "Climategate" had no effect on the APS position because it was irrelevant to it, except for emphasizing the need for making the statement in the first place--people that are ignorant of the science are easily distracted by lies and misdirections of the denial side. Apparently even people that should know better, like Hal Lewis, can also be distracted. Maybe he wouldn't have been when he was on the top of his game, but his association with the JASON group of theoretical scientists that did military work probably has made him more conservative.
However, I could mention that Walter Munk, a more eminent (and older) scientist than Lewis--that is still active in science, does believe in AGW.
I don't really understand why deniers obsess on the few scientists that don't believe in AGW while ignoring the thousands that do. I guess they will cling to anything to desperately support their denialism in the face of evidence that mounts daily.
EDIT: Ottawa Mike in fact I did address YOUR question and HIS letter. You are the one that's claiming he's a leading scientist--I'm saying he was a somewhat prominent scientist, many many years ago, but he is not now--and that you're ignoring the thousands of current scientists, some of which actually qualify as leading scientists.
I addressed his letter through my allusion to "Climategate." The fact that that is one of the main points of his letter shows that he is not only out of touch with the science but in no position to judge the actions of other scientists. Frankly, I take that as evidence that the guy sits around listening to Fox News and Rush Limbaugh these days. Multiple investigations of the hacked emails show no evidence of fraud or malfeasance, but deniers like yourself and Lewis keep going over them again and again in your minds, weaving vast conspiracies out of them.
Similarly this is at least the FOURTH question on what is essentially non-news: a retired scientist letting his membership lapse in a professional society because he doesn't like the society's position on a field in which he is untrained and hasn't done research. Somehow you think his opinion weighs more importantly than the thousands of active scientists in that field. I don't get it, who cares what Lewis thinks? Frankly, I do listen to people like William Gray or Roger Pielke when they have doubts about AGW. Hal Lewis? I don't think so. You should at least look to people trained in atmospheric science to support your position.
One more EDIT: Just for kicks, I re-read his letter one more time. It is all about appeal to authority--his purported authority--and has zero physical content. Nothing is based on physics--it is all about conspiracies. I'm sorry to say this, because Lewis has had a distinguished career, but now the letter just sounds like the ravings of one more conspiracy theorist.
HIS AGE: There has been a lot of speculation on his age. For the record he was born October 1, 1923, making him 87 years old. Don't infer anything from this, I just thought I'd end the speculation about it.