James Lewis has written a wonderful explanation for non-scientists as to why the whole 'global warming' hue and cry should be taken with a grain of crystalline Sodium Chloride:
Why Global Warming is Probably a Crock
As a scientist I've learned never to say "never." So human-caused global warming is always a hypothesis to hold, at least until climate science becomes mature. (Climate science is very immature right now: Physicists just don't know how to deal with hypercomplex systems like the earth weather. That's why a recent NASA scientist was wildly wrong when he called anthropogenic warming "just basic physics." Basic physics is what you do in the laboratory. If hypercomplex systems were predictable, NASA would have foolproof space shuttles -- because they are a lot simpler than the climate. So this is just pseudoscientific twaddle from NASA's vaunted Politically Correct Division. It makes me despair when even scientists conveniently forget that little word "hypothesis.")
OK. The human-caused global warming hypothesis is completely model-dependent. We can't directly observe cars and cows turning up the earth thermostat. Whatever the human contribution there may be to climate constitutes just a few signals among many hundreds or thousands.
All our models of the earth climate are incomplete. That's why they keep changing, and that's why climate scientists keep finding surprises. As Rummy used to say, there are a ton of "unknown unknowns" out there. The real world is full of x's, y's and z's, far more than we can write little models about. How do you extract the human contribution from a vast number of unknowns?
That's why constant testing is needed, and why it is so frustrating to do frontier science properly.
James then walks you through some basic arithmetic and statistics and closes with the following:
The Bottom line: our best imaginable model has a total probability of one out of three. How many billions of dollars in Kyoto money are we going to spend on that chance?
Or should we just blow it at the dog races?
So all ye of global warming faith, rejoice in the ambiguity that real life presents to all of us. Neither planetary catastrophe nor paradise on earth are sure bets. Sorry about that. (Consider growing up, instead.)
That's why human-caused global warming is an hypothesis, not a fact. Anybody who says otherwise isn't doing science, but trying to sell you a bill of goods.
Personally, after looking at the data and the historical record, I think that we are entering a period of warming but the idea that it is human-caused is ludicrous. The earth is so much bigger than we are ever going to be and the natural cycles swamp anything that man can accomplish. This cycle of warming and cooling has been going on every 400 years for the last several thousand and there is precious little that we can do to stop it or to change it.
