The Scottish philosopher David Hume (1711-1776) destroyed philosophy with logic.  His skepticism has not been, and I believe never will be, adequately answered.  Were he alive today, I believe he could do the same with climate science, and through the same mechanism.

Hume unassailably pointed out that we can never know with absolute certainty what causes the effects we observe.  All we know for sure is that we can’t know for sure.  ‘A’ may always precede ‘B’ in our observations, but that does not mean A causes B, and even if there seems to be a causal relationship, we can’t assume the relationship will always hold.  The future often looks like the past, but there is no cosmic reason that it must.  (Incidentally, neuroscience has discovered that in some instances our minds will make us perceive that A precedes B even when it doesn’t, if our minds have–subconsciously, of course–concluded that A preceding B is the best way of presenting reality to our consciousness such that our body might better survive and prosper.)

Just because every instance of hitting a billiard ball with a cue ball causes movement in a predictable direction and velocity does not mean that we can, with100% certainty, expect that the next strike of the ball will do the same.  Gravity could be suspended.  The arrow of time could reverse.  Any number of assumptions we make about the world as it is (light speed, gravitational forces, molecular forces, etc.)—and particularly the assumption undergirding all others—that things will stay as they are–might change to destroy our causative analysis.  In the end, all we have are correlations.  A billiard ball is hit by a cue ball with a force sufficient to overcome friction such that it moves.  The billiard ball doesn’t move without which it is hit.  We never see effect B without also seeing cause A.  Yet still, we’ve done nothing but describe a conjunction, and one that could fall apart at any moment, if our underlying premise—that the future should look like the past—fails.

But skepticism so cosmically radicalized is of no use to us in trying to figure out the world.  We must assume that effects have discernible causes—that the future will in fact look something like the past; that the same rules that prevailed in the past will apply in the future–or the whole enterprise of discerning the nature of reality fails.  To live in the world, we must suspend disbelief.   Yet even when we dispense with the cosmic level of skepticism, there is the simple correlative problem:  Just because two things appear together does not mean that the two have a causative relationship.   Snow melts in spring, which is followed quickly thereon by trees budding leaves.  Did the snow melting cause the trees to bud?  No, the same phenomenon that caused the snow to melt—the change of seasons—caused the trees to bud.

Imagine the fun Hume would have with climate science.  The basic theory, as I understand things, is that atmospheric temperatures on the surface of the earth (the troposphere) are increasing due to mankind’s activity; particularly, that the burning of fossil fuels is causing carbon dioxide in the troposphere to increase, which is in turn, due to the greenhouse effect, causing the troposphere to warm.

How much of the science is certain, even disregarding Hume’s skepticism?  First, is the troposphere actually getting warmer?  That’s not as easy an assertion to make as it first appears.  Take out a globe and spin it a few times.  Turn it upside down, so you can see the Southern Hemisphere better, and spin it some more.  What is the most prevalent feature?  Oceans.  Over 2/3rds of the earth’s surface is covered with them.  How many temperature reading stations, i.e., mainly ships, do we have/have we had/ on the oceans?  How many do we have now relative to two hundred years ago—or, roughly the beginning point for measurements that are interpreted to show the earth’s surface is getting warmer?  Likewise, on land, how many of our measurements are taken in and around big cities with automobiles and factories and electrical devices all generating massive amounts of heat in densely-populated areas?  Wouldn’t it be surprising to find that cities were not warmer today than they were two centuries ago, before all of mankind’s heat-generating mechanical devices found concentrated usage in them?  To make a valid comparison, we must have comparable temperature readings, in the coverage, in the sensitivity of the instruments taking the measurements, and in the conditions under which the measurements are made.  To make a valid comparison, we must hold constant every other variable except temperature.  Have we?

The answer is no, it is not possible that we have held every other variable constant except temperature.  It is not possible that we have had the same coverage, the same sensitivity of measuring instruments and the same conditions under which the measurements are made the world over for the last two hundred years.

There is no way we can know for certain, or even know to within a reasonable measure of doubt, that the troposphere is warmer now than it was two hundred years ago.  If the troposphere were indicted for warming, there is no way it could be convicted of the crime, except circumstantially, and circumstantial evidence is not forensic, scientific evidence.

But, for the sake of argument, let’s anyways assume that we know the troposphere is warming.  Can we know it’s cause?  Even without invoking Hume’s skepticism, the answer is emphatically no.  Ascertaining causation requires the isolation of variables.  It requires holding all things constant other than the variable in question (carbon dioxide, for the climate change theory) to tease out correlations that might yield causative linkages.  But it is not possible to isolate climatic variables.  We have no way, for instance, of holding the sun’s radiation constant, or of even knowing its variations over the last two hundred years.  We can’t know how much of the heat that the earth itself generates reaches the surface.  We can know a bit about sunspots and volcanism, but knowing a bit is not knowing with any certainty.  We know the sun and the earth generate heat.  The sun’s heat, very obviously, arrives to the troposphere after traveling roughly 93 million miles through relatively empty space.  The earth’s heat bubbles to the surface in a myriad of ways.  Do we know how much heat was reaching the surface through oceanic vents two hundred years ago?  Not likely, as we weren’t even aware of them until the last half century.  Do we know today of cosmic aberrations that might have interfered with the sun’s radiation reaching the earth two hundred years ago?  93 million miles and two hundred years is a vast stretch of space and time to hold things otherwise constant.

Unable to hold all variables other than carbon dioxide constant, perhaps we could account for changes in the variables, but doing so would require knowing how other variables, like solar radiation and volcanism, have changed over the years, something that we simply do not know, nor have the capacity to find out.  Claims to the contrary are flights of speculative fancy.

So, even were we certain that the troposphere had warmed over the last two hundred years, there is no way, with any reasonable level of certainty, that we could possibly know why.  And that’s even without questioning our knowledge of carbon dioxide levels in the atmosphere.  Do we really know, except for the recent past during which we have actively monitored carbon dioxide levels in the atmosphere, what the carbon dioxide levels in the atmosphere were two hundred years ago?  When we didn’t even know what carbon dioxide was?  Greenland ice cores are nice, but a poor substitute for real-time measurements.

So, maybe Hume wouldn’t have so much fun.  His logic needn’t be carried to its skeptical conclusion to understand that climate change science is a tower of speculation built on a foundation of sand.  Nothing of this means that climate change theory is necessarily wrong.  It means that it is not certain.

But there’s another aspect of Hume’s genius that helps explain the phenomenon of climate change theory’s widespread acceptance.

Hume observed that “Reason is, and ought only be the slave of the passions.”  People have come to passionately believe, and not unreasonably, that mankind is wrecking the planet.  We pollute the rivers, oceans and atmosphere without a thought.  We clear the jungles of the wild to build concrete and steel and asphalt human jungles that we hubristically call civilization.  We scrape and bore and tunnel into to the earth to pull from it the vast energies of ancient suns stored there, releasing the energy in chemical reactions the world over, combining carbon with oxygen just as our bodies do, to heat and cool and power the activities of mankind.  Ninety-six million barrels of oil were burnt today, and will be burnt tomorrow, and every succeeding tomorrow as far as the eye can see.  Almost nine billion tons of coal were burnt last year.  And there’s no reason to think this year will be any different (Hume’s admonitions aside).

How is it possible that all this has no deleterious effect on the earth’s environment? How can this not be harmful from the perspective of the earth’s ability to support human, and other, life?  We see the destruction we have wrought and we passionately understand that this can’t go on forever, and so send our reasoning minds scurrying to find an answer, to pinpoint a deleterious effect that can be traced to some cause identifiable with our activity.  Global warming, or climate change as it is now known, fits the bill (if rather imperfectly, as human beings, and life in general, does better, to a point, in warmer environments than in cold—the return of the ice age would be a catastrophe of epic proportions).

People who are passionately concerned about where all this “progress” and “development” will ultimately lead set their enslaved reason to the task of figuring out why what their intuitive feelings are correct.  And climate change science provides it.  The theory that the earth is warming and mankind is causing the warming through his burning of fossil fuels sounds reasonable and logical, and that’s good enough.  It needn’t actually be reasonable and logical.  It needn’t actually adhere to the gold standard of science—that only falsifiable theories have the capacity to enhance our understanding of the world.

A theory needs to be falsifiable if it is to rise above mere speculation.  Being falsifiable means that data could prove the theory wrong.  While over a very long time period—much longer than the human life span at least—climate change theory might have its viability questioned (if, for example, by the beginning of the next millennium, the earth is entering a new ice age, even as we kept burning oil all the way through this one), it can’t ever be conclusively falsified, so it also can’t ever be conclusively proved.  There are simply too many variables of varying importance at play, and over too-long a time horizon.

Some theories that seem also to be unprovable by falsification are only superficially so.  The theory of evolution has a problem similar to climate change theory—the time horizons are too long to render a definitive proof (except in the case of single-celled organisms, which we can watch evolve in real time under microscopes).  But the time horizon is only a problem if we misunderstand the essence of the theory.  Evolution science says that life must come from life and be adaptable to the environment in which it finds itself, the mechanism for adaptability being natural selection.   If mankind were to witness God, or something, breathing a human into being from a block of clay, and one that had supernatural powers enabling it to exist without concern for its environment, the theory would then be falsified.  That hasn’t happened to date, so the theory is sound.  There is no commensurate (if in my example, ridiculous) event that could falsify climate change theory.

But the people who have become passionately devoted to climate change have their hearts in the right place.  We are befouling our planet.  We are, with our agriculture, our vehicles, our lifestyles, etc., altering the earth’s biota, and the earth’s ability to support life in the future, in irreversible ways.  We can’t keep doing this forever, or for even much longer.  So, I am loath to acknowledge the fallacies of climate change theory, if climate change theory is all we have to compel us to change our ways.  My heart is with the climate change crowd, but my head won’t follow.  It’s a problem I have, that my head is not such a good slave to my passions.  I was born with Hume’s skepticism, but even Hume knew better than to follow his skeptical head.  Had he tried, he would never have accomplished anything.  And maybe that trifling fact explains and justifies climate change theory better than anything else.