What do we know about what we know? Consider the following two examples.
The first: It takes 365 days for Earth to orbit the sun, right? Not exactly: Every four years we have a leap day, which means an actual "year" is 365 days and six hours.
But that's not precise either, because there are no leap days in years evenly divisible by 100, except the subset of years evenly divisible by 400 - which is why there was a Feb. 29, 2000, but there was no extra day in February 1900 and won't be one in 2100.
All of which leads inexorably to the conclusion that the earth doesn't actually orbit the sun.
Now, the second: Whether you believe he is the son of God or not, there is ample evidence that Jesus was not an only child.
Yet scholars of the period like John Crossan are unsure exactly how many siblings Jesus had. Some evidence also suggests his older brother, James, who was also known as "Christ," was stoned to death for being a political agitator. (Perhaps the scriptures deified the wrong rebel?)
Given so much confusion and so many gaps in the historical record, clearly Jesus never walked the Earth - which, by the way, doesn't orbit the sun.
If my logic above seems absurd, you must be equally frustrated by the latest chicanery perpetrated by climate change deniers. What they want you to believe, first, is that one scientist's use of a common methodological conversion, which he unfortunately described as a "trick," is proof that global warming is actually a "trick"- as in hoax - being played on all of us.
Because the Earth's orbit time, measured in years, is not perfectly divisible by its rotation time, measured in days, the use of leap days is a legitimate "trick" to synchronize the two. Does making this slight adjustment call into question the fact that the Earth orbits the sun, or that it does so roughly once every 365 days? Of course not.
Deniers would have you further believe that the absence of some complete, perfect data set on climate change disproves that the planet is warming. But omissions and discrepancies in the climatic record do not dispel the evidence for warming any more than disagreements in the Gospels dispel Jesus' existence altogether.
As Brad Plumer, The New Republic's environmental reporter, reminds us, there are two potent and ineluctable realities about climate change: One, releasing carbon into the atmosphere traps heat against the Earth; and two, humans have been pumping billions of tons of carbon into the atmosphere, much of it during the past century and at increasing rates as world population and productivity grew.
These are not opinions or "theories." This first is a physical fact, the second a demonstrable trend. To deny the former is akin to denying that gravity exists. To ignore the latter is equivalent to pretending that coal mines in West Virginia or gas stations in Westminster are imaginary.
Yet these are the absurdities and self-delusions in which deniers traffic. There are tricks to the global warming trade all right, but they are being played by deniers, not on them.
None of which is to assert scientists know everything about climate change. How much of global warming is caused by human carbon production; how much damage that carbon is causing the oceans and atmosphere; what the environmental impacts on humans and other species will be - these are legitimate areas for further study and debate.
But those who knowingly misrepresent a scientist's e-mail, or who use a legitimate disagreement among scientists to cast a black shadow of doubt across the entire issue, are manipulating inherent imprecision to distract, if not deceive.
Oh, and when scientists acknowledge that all theories, including their own, are unprovable, beware of those who shout "Aha!" All theories are by definition unprovable - but some survive repeated attempts to debunk them. And climate change is one of the stronger survivors.
In climate change or other epistemological disputes, remember this: Anybody who tells everybody that because we don't know everything we therefore know nothing is somebody that nobody should listen to.
Thomas F. Schaller teaches political science at UMBC. His column appears regularly in The Baltimore Sun. His e-mail is firstname.lastname@example.org.