If even slight global cooling remains evidence of global warming, what isn't evidence of global warming? What we have here is a nonfalsifiable hypothesis, logically indistinguishable from claims for the existence of God. This doesn't mean God doesn't exist, or that global warming isn't happening. It does mean it isn't science.
He then goes on to offer three explanations for believing in gw -- ideological (serving as a conduit for your political views), theological (i.e. humans and their by-products are inherently bad, so we need to "tread lightly" as it were) and psychological (a penance system, aka carbon credits).
The psychological aspect, to me, has more to do with providing the basis for the other two motives. In the case of ideological convenience it has to do with the rich and powerful (read: celebrities and politicians) getting off on controlling your life -- telling you what you can drive, what you can illuminate your house with, etc. Those who do it are doing it with your entertainment dollars or votes in their pocket. You've given them value, therefore their edicts (in their minds) are obviously canonical.
The psychological basis behind the theological motive is what I believe to be an innate sense of being morally accountable to something bigger than us. We may do that in varying degrees through our religious beliefs, or if lacking any belief perhaps through the betterment of mankind, family, etc. The average joe driving his Prius preaches self-loathing and capitalistic abstinence (and at times may also exercise the two), looking down his nose as those who don't. It's his mode of worship and should also be yours. It doesn't matter which religious or non-religious belief system he espouses, the mad pursuit of being ecologically friendly is his method of attaining moral justification.
All of this is to ask, does the message of gw arrive with a sense of genuine concern for you and what's important to you, or does it arrive with a sense of "knowing better than you" ?