Consider the political juggernaut that is sweeping the earth, browbeating the leaders of the world's nations in an attempt to coerce them to reduce their CO2 emissions.  Its protagonists point to the predictions of computer climate models as the basis for their draconian calls to action.  They point to science, right?  Well, the folks that push this extreme agenda would like us to think that it's science - and the modeling of climate is indeed a valid and important scientific endeavor - but our evaluation of that endeavor, and our decision to do, or not do, something about it, is really an act of faith.

That such is so may readily be deduced from a recent news item in Science, where contributing correspondent Barry Cipra reports on a pair of scientific workshops designed to explore the subject of uncertainty in computer models of complex processes, such as global climate change.  He notes that computer models are wonderful things, that they can do in minutes to days what it would take a person with a pencil and paper millennia to accomplish.  But the precise numbers and realistic pictures produced by computer simulations, he says, are but "an illusion of accuracy" and that "a ravening swarm of assumptions, simplifications, and outright errors lurk beneath."

Knowing these facts complicates things.  The boundary between science and belief begins to blur.  In fact, people with an opinion on the subject typically express their position with respect to CO2 and climate change more in terms of intuitive feelings than cut-and-dried facts, when they say they either believe the predictions of the models or have no faith in them.

The appropriateness of this terminology becomes even clearer when the nature of the computer modeling enterprise is explored in a little more detail.  In the case of global climate change, for example, there is a degree of uncertainty associated with each of a very large number of variables that enter into the computations; and as Cipra notes, "researchers must figure out the uncertainties in each step of the model and see how those uncertainties build on each other."  Furthermore, Cipra quotes MIT's Gregory McRae as stating that "as we put more of our understanding into these models, it's getting harder to probe their uncertainties."

So it really is a matter of faith.  Do we, for instance, believe that we understand all of the processes - physical, chemical and biological - that simultaneously operate to produce the climatic state of the earth at any given time?  Indeed, do we believe that we even know all of them?  Or the ways in which they interact with each other?  Likewise, do we believe in the accuracy of the mathematical representations of these myriad processes?  Clearly, everyone - on both sides of the issue - makes such determinations; and they are based on a principle that transcends science.  Indeed, that principle passes judgment on science.

But to continue, what about the uncertainties associated with various internal and external forcing functions?  Do we have faith in our representations of them?  Or in our projections - which require models within models - of how they will vary in the future?  How about perturbations that cannot be predicted at all, but are known to occur and have climatic consequences?  Things like explosive volcanic eruptions, hydrothermal happenings at the bottom of the sea, and dramatic changes in the routes and flow rates of ocean currents, things we are just now beginning to understand and, therefore, hope to be able to model (hopefully accurately) someday.

Truly, uncertainties plague us; and they will continue to plague us for the foreseeable future.  And it's not just a matter of "garbage in, garbage out."  Sometimes it's "good stuff in, bad stuff out," when we do not know enough of the good stuff that is required to give us a correct result.  Furthermore, even the best of results that could ever be hoped for will not provide a firm answer to the climate change question.  There will always be error bars or probability levels associated with whatever is predicted.  And how can we know if these measures of uncertainty are even correct?  Clearly, our evaluation of the situation will ultimately come down to faith, one way or the other.

But don't get us wrong.  We're not talking about blind faith, or about faith based on some opposing world-view or philosophy.  We're preaching eyes-wide-open faith, faith that is predicated upon actual observations of the real world.  Faith, for example, that the sun will rise tomorrow, because that has been our collective historical experience, and the experience of science itself.

Hence, we continue to demand that advocates for disruptive social and economic change "Show Us the Science" upon which they base their calls for action; but we recognize that everyone must ultimately evaluate that science for himself or herself (Science and Trust: Are They Compatible?).  And in this very personal endeavor, reason-based faith - or the lack thereof - in the robustness of the science employed will play a very important role in helping us to make an informed decision on all sorts of subjects, not the least of which is that of carbon dioxide and global environmental change.