I've been reading through several comments...
What I'd like to know (and have wanted to know for a while) is how much data** do we actually have about this stuff? By that I mean, how many points on the globe have been measured, how well distributed are they (not just clumped together in a few small areas), how many readings a year are taken, how many years back they have been taken, etc.
As was pointed out with London possibly having a 3rd white Christmas... that's ONE location on earth. Further, do we have data going back farther than 50 years? If so, what are the answers to the questions above for that 50 years? Then go back 100 years. Then 150, 200, etc. While I've not looked into it, I doubt we have accurate data going back 200 years or more in the amounts we have nowadays or in the distribution we (may) have.
If we don't have data going back sufficiently far enough then how can we say this is definitely not part of a natural cycle? Further, even if something we're doing is having an effect, how can we presume that the earth doesn't have sufficient mechanisms in place to self-correct in time despite any increase in CO2, GHG, or other chemicals from mankind? Yes, I get it that sitting on our hands may be a problem if it really is rising and continuing to rise without a self-correct mechanism from the earth (or even the solar system for that matter). But, it's extremely hard for me to take people like Al Gore or other alarmists seriously when they're declaring the destruction of the earth and others (with more knowledge, experience, and authority) are saying no, it's not that bad. It's even harder when the alarmists' solution has that eery ring of global redistribution of wealth and communism. Yes, I'm bringing politics into the discussion, but that's what Al Gore and others have done, so I think it is fair game to discuss the political motivations of those crying out for change in industrial practices and social changes "for the greater good".
** Where data is absolute temperature, along with what else was going on at the time... no rain, tons of rain, storms, other natural factors.