What Can You Say to Climate Deniers?

One of the most often cited facts by climate deniers is the known history of climate fluctuation in the recent geologic record.  The idea is that we know climate fluctuates naturally, so that changes in weather patterns need not be related to any man-made condition. When those of my generation were educated about climate the idea that vast ice sheets once covered northern states was already established. The cause of those past conditions was a mysterious natural part of the earth’s climate system.  Any human-induced climate effects would surely pale in comparison with these much more dramatic and well-documented changes. In fact, we should really appreciate the divine blessing of fossil fuels.  They ensure our comfortable survival when climate turns colder.  They provide for air conditioning and irrigation when things get hotter.  Global warming is just a distraction created by liberals to cripple the energy industry in its effort to insulate us from inevitable natural climate variation. Those much-hyped feedback effects are just so much hypothetical malarky.

Sixty years after I graduated from high school, the cause of ice age climate is much better understood.  The real lesson from that understanding is how tiny thermal effects have driven those wild swings in climate and global temperature. Those thermal fluctuations are so small that the initial suggestion for the cause of the repeated glacial episodes by an obscure Serbian mathematician was dismissed as preposterous.  Only the isotopic calibration of ocean cores with a steady and continuous record of deposition in the 1970’s could finally show that those calculated fluctuations coincided exactly with the sediment record.  So what was that source of those extreme but slow climate fluctuations?  They are driven by the precession of a slightly elliptical earth orbit, with the season of closest approach slowly varying from summer to winter and back to summer again.  Incoming solar heat in summer is slightly less than average on a 22,000-year recursion cycle.  Ice builds up in spurts during those cooler summers and solar reflection from ice prevents complete melting during warmer summers – the derided feedback effect in spades.  The volume of ice ratchets up in this fashion until the ice sheets become so extensive that they starve glaciers of moisture (cooler air holds a lot less water) and ice sheets collapse.  All of this driven by changes of only a few percent in the distance of the sun from the earth between summers in the cycle.  Arguments that global warming will simply offset a cooling trend as we enter the next cycle aren’t relevant, either.  Evidence of the environment in the first ratchet step in the last grand cycle from places like the famous Snowmastodon* site shows that the first cool part of the cycle is not even registered at mid-temperate zones and remains confined to just the polar regions.

Snowmastodon Site

Calibrated model predictions of climate imposed by the 22,000-year cycle show that very little such solar cooling would be expected without human intervention for many thousands of years.

When understanding the causes of recent glacial-interglacial cycles underscore how sensitive earth climate is to very small changes in the distribution of solar heating, remember that human induced climate change is being applied in a different way.  Slight increases in solar radiation are absorbed differentially on land versus sea, driving the monsoonal patterns that were more intense during the warmest geologically recent times.

These small changes can have a real impact on humanity. The fossil record shows that the arrival of anatomically modern humans at the Carmel Caves of Palestine coincided with a time when monsoonal rains created a green Sahara to provide a suitable pathway out of the south African savannah. In contrast, a significant change in CO₂ content of the atmosphere would be applied over land and sea alike and not simply drive intensified monsoons. On top of that, the changes we see in geological records extend over the period of the orbital forcing cycle on the scale of thousands of years. Is there any indication that a much faster rate of change will overcome “climatic inertia” within the coming century?  Abrupt warming cycles have been repeatedly found in glacial times within cores from the Greenland ice cap (Osher-Dansgaard cycles).  Some argue that this was just a polar phenomenon in the local Greenland environment – perhaps local switching of a minor branch of the Gulf Stream.

Most land-based cores in North America do not extend back more than 20,000 years into the central heart of the last cold period.  But one deep core from a subsiding basin in Virginia goes back 130,000 years and clearly shows these abrupt cycles – strong evidence that the climate can be abruptly shifted over large regions within a human lifetime or two.

After dismissing attempts to minimize the possibility of man-made climate change it is worth contemplating the severity of the changes in climate that the Ozarks have experienced.  How different was the environment at the height of the last glaciation in the Ozarks?  Twenty thousand years ago, the continental ice sheet extended down to the middle of Iowa.  Permafrost or discontinuous permafrost held much of Missouri in its grip.  The southern part of The Ozarks (Boston Mountains) would have been a mosaic of coniferous pine-spruce forest and steppe with some of the hardiest deciduous trees in protected locations.  The maximum extent of continental ice sheet would have coincided with a distinctly drier atmosphere – the dry conditions that would have starved the ice sheet and lead to its sudden collapse.  We see colonies of prickly pear cactus on the driest and most exposed rock ledges along the Buffalo River.  We think of these as relicts from times with a bit more drought and slightly higher temperatures. But, more likely, they are relicts of a more widespread population during much drier glacial times. The same species are abundant today on the cold, dry steppes of eastern Montana.

There are few places in our region where one can envision past climate extremes to obtain a feel how such small changes in solar heating can have a profound change in the world we inhabit. Famous springs in southwest Missouri have yielded the bones of extinct mastodons that are associated with fossil needles and cones of jack pine, a species that grows throughout eastern Canada. The best place to envision ice age Ozarks is at Cupola Pond in south-central Missouri.  It’s a site within the Mark Twain National Forest that can be found on the internet and associated with a now poorly-maintained display at the end of a narrow forest road.

The “pond” is fully forested and has shallow standing water for most of the year.   The depression holding the pond is an example of how tree species can find tiny bits of suitable habitat far from their main range.  Here the shallow “pond” is forested with water tupelo and pin oak, two trees known for growing in poorly drained habitats with long periods of standing water.  A sediment core taken from the pond shows that the surrounding forest was dominated by cycles of boreal jack pine and spruce with a small amount of oak and ash.

Spruce is clearly a tree of the far north but pine can grow anywhere from Hudson’s Bay to the gulf coast.  Needles and cone fragments show that the pine at Cupola Pond was the boreal variety.  Pollen experts often compare zones they find in pollen cores to “analog” pollen collections at various distant locations. The best analog for Cupola Pond 20,000 years ago is south central Manitoba along the shores of Lake Winnipeg.  Having worked in that area I saw a forest with large stretches of uniform jack pine and intervening areas where pine was yielding to spruce in a landscape subject to occasional conflagrations. The one prominent deciduous tree was bur oak with local wetland stands of black ash – both known as the northernmost ranging members of their genus. The cycles of pine and spruce domination seen in the pollen core are likely telling us about cycles following regional fire events that are so prominent in Canadian boreal forest today. Just thinking about an effective climate transfer over the distance from Fayetteville on the White River to Winnipeg on the Red River of the North is dramatic emphasis of how sensitive our climate is to what would seem like negligibly small changes in amount of solar input.

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*FOOTNOTE: The so-called Snowmastodon site is a buried lake deposit dating back to the last interglacial with fossils extending upwards through subsequent cold periods unearthed by a construction project at Snowmass resort in the Colorado mountains. The site named for the bones of mastodons (plus camels and horses) that washed into the lake during climate cycles before filling up entirely.