The American Thinker has an article, written by a scientist, explaining very clearly just why Anthropogenic Global Warming (AGW) enthusiasts really need a reality check.
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?
Now there's a basic fact about complexity that helps to understand this. It's a point in probability theory (eek!) about many variables, each one less than 100 percent likely to be true.
If I know that my six-sided die isn't loaded, I'll get a specific number on average one out of six rolls. Two rolls of the die produces 1/6 x 1/6 = 1/36. For n rolls of the die, I get (1/6) multiplied by itself n times, or (1/6) to the nth power. That number becomes small very quickly. The more rolls of the die, the less likely it is that some particular sequence will come up. It's the first thing to know in any game of chance. Don't ever bet serious money if that isn't obvious.
Now imagine that all the variables about global climate are known with less than 100 percent certainty. Let's be wildly and unrealistically optimistic and say that climate scientists know each variable to 99 percent certainty! (No such thing, of course). And let's optimistically suppose there are only one-hundred x's, y's, and z's --- all the variables that can change the climate: like the amount of cloud cover over Antarctica, the changing ocean currents in the South Pacific, Mount Helena venting, sun spots, Chinese factories burning more coal every year, evaporation of ocean water (the biggest "greenhouse" gas), the wobbles of earth orbit around the sun, and yes, the multifarious fartings of billions of living creatures on the face of the earth, minus, of course, all the trillions of plants and algae that gobble up all the CO2, nitrogen-containing molecules, and sulfur-smelling exhalations spewed out by all of us animals. Got that? It all goes into our best math model.
So in the best case, the smartest climatologist in the world will know 100 variables, each one to an accuracy of 99 percent. Want to know what the probability of our spiffiest math model would be, if that perfect world existed? Have you ever multiplied (99/100) by itself 100 times? According to the Google calculator, it equals a little more than 36.6 percent.
Remember - this chap isn't saying that there is a 1 in 3 chance the AGW crowd could be right, he is saying that the BEST they could EVER hope to be able to predict the human effect on climate change is 1 in 3. The fact there are quite a few more than 100 variables and that few - if any -are known to 99% accuracy should give you some idea of just how far way they are from that right now. His conclusion?
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.