Yes the world does cycle on 20 year(I forget, but I'm pretty sure that's right) cycles. Yes, most of the time when they talk of global warming they leave this part out. Yes, that could be considered immoral not to mention, but there are too many people out there that would use the warming cycle as an excuse as to why there is no global warming.
Of course both sides will skew facts and figures so they are right, but you have to look at where the science comes from, who is supporting it, and what the motive is for figuring it out. I remember not so long ago people saying not only are cigarretes not harmful, but they are actually helpful. Who is on the side of no global warming? Mainly, these people are the big business, the oil companies, the people who have pretty much made themselves on the fact that they create mass amounts of greenhouse gasses. Who is on the side of global warming? Environmentalists, activists, scientists, people who are considered the caring side.
If it is a choice between believing environmentalists or capitalists, I will go for environmentalist, because I truely believe they have less to personally gain(unless you look at the earth as an asset). I've learned that the person who gains less from their position is usually the one who is less inclined to actively pursue their point. This means that many of their gain is centralized on truely helping the earth. You really cannot trust the science on either side because of the predominent skewing of facts and figures. All I know is that I'm sitting here in February and it is 80degrees out. I've never been in the dead of summer and said, "I'm so cold right now, I think I need a jacket."