It's has fascinated me that climate models assume that the forces driving atmospheric events are, more or less, linear. If this were so, there would be no point in the complicated, super-computer hosted, "global general circulation models". A single simple function/equation would suffice. Increase force "x" and see increased consequence "y". I see SKEPTICS reducing the models to such equations, but I don't see the consensus IPCC team explicitly making that claim. In general the scientists seem to accept that the climate is an aggregation of various regions' weathers. The aggregation can be MODELED, but not CALCULATED. However, the consensus finds that by good luck the models, over the range of expected forces, react in a linear fashion. This is rather surprising given that Lorenz, who more or less discovered the mathematics of chaos, was attempting to model weather. Weather, Lorenz found and the modern IPCC continues to quietly affirm, is chaotic.

The IPCC fans, if not the IPCC science teams themselves, have picked up a term popularized by Gladwell called "the tipping point". It is analogous to a science fiction concept of "the Singularity", and the math concept of discontinuties. At some point along the plot of a function an input value results in a wildly different output value. It is unlike what came before, moves at a different slope, at a different direction, it may not even exist among the same domain of values as what came before. The fans of the IPCC embracing the tipping point also -- I think in consequence -- embrace the idea of the global temperature index "escalator". The average temperatures are stable a while, despite forcing, then suddenly show a discontinuous increase, then, for another little while, stabilize again, until they increase again. This validates for them the notion that at the small scale, regional, "weather" level all climate science remains, as has been well established, chaotic. But the escalation is well modeled, they suppose by a steady trending increase.

But if the climate, like weather, is chaotic; is there ANY reason to suppose that continued forcing will continue to produce changes in the same direction? Of the same magnitude?

The geological record is filled with the plots of temperature proxies whose chronological charts show abrupt, large, discontinuous FALLS of average climatic temperatures. Temperature rises are, so far as I am aware, all rather slow, where they exist in such records.

Assume for the sake of discussion that the broad outlines of the IPCC overview remain correct. Mankind can influence the climate. CO2 is the main driver of that influence. The problem is "baked in" and "getting worse". That "even if we stopped all emissions tomorrow" ... etc. Why shouldn't the world's leadership prepare for catastrophic COOLING, as one of the consequences of this terrible situation?

Has everyone seen the Lorenz-ian waterwheel? http://www.youtube.com/watch?v=7A_rl-DAmUE As the trickle of "force" (falling water) increases, the "trend" (direction of spin) slows, then reverses.

What if the IPCC is *CORRECT*? What if the pause of the past two decades is NOT evidence that they are wrong, but that the accumulation of CO2 forcing has slowed the old trend just prior to a reversal? What if we *ARE*, all doomed, but not to drought and heat but to freeze in the dark?

This of course presents the policy makers a whole different set of problems.

On the other hand, couldn't an IPCC general circulation modeler salvage his reputation by tweaking the runs to show such a catastrophic reversal? The science would still be right, the incentives to tax CO2 would still be there, but the EVIDENCE of the problem would become utterly immaterial. If warming continues, they were right. If warming slows, "it is worse that we thought", and if cooling re-occurs, then "why didn't you fools listen to us?"

A skeptical policy maker might then be inclined to dismiss the whole field of science -- if it can predict up from down or left from right, why bother?

But as a true skeptic of SCIENCE, I'm wondering what kind of data could help draw the distinction. What can be measured to determine a difference between "natural variation" and "tipping point / chaotic trend reversals"?