The question of which came first, the chicken or the egg, is an age-old question.  It is a metaphor to describe situations where it isn’t clear which is the cause and which is the effect when two interrelated events are considered.

Aristotle first pondered the question in the fourth century B.C. and concluded it was an infinite sequence with no real answer.  But Plutarch wrote in the first century A.D. that this question was as important as whether the world had a beginning.

But in the world of climate science, we often ask, “which comes first, the change in air temperature, or a change in greenhouse gas concentrations?”

Since the dawn of climate change alarmism, we have been told that carbon dioxide is the driver of climate change; for scientists in this camp, it is the climate control knob.  Increase carbon dioxide, and consequently, air temperature increases.  Decrease the atmospheric concentration of carbon dioxide—and methane and nitrous oxide—global warming will be abated.  For the climate alarmists, it’s just that simple. 

Or is it?  Many climatologists have noted that carbon dioxide is not the climate change driver alarmists purport it to be.  A recent article in the Epoch Times suggests that a fixation on carbon dioxide ignores the real drivers of air temperature, which include the Sun and natural variability.  But the idea that carbon dioxide is somehow the climate change control knob is an integral part of the climate alarmist narrative.

And despite evidence to the contrary, this narrative always must be pushed.  For example, in 2007, Laurie David and Cambria Gordon published a book entitled The Down-to-Earth Guide to Global Warming.  It was billed as “from the producer of [Al Gore’s] An Inconvenient Truth comes a powerful, kid-friendly, and engaging book that will get kids get interested in the environment!”

On page 18, a flap instructs children to “lift to see how well carbon dioxide and temperature go together.”  The graph that becomes exposed shows that as time passes over the last 650,000 years, “the more the carbon dioxide in the atmosphere, the higher the temperature climbed…the less carbon dioxide, the more the temperature fell…by connecting rising carbon dioxide to rising temperature[,] scientists have discovered the link between greenhouse-gas pollution and global warming.”

The figure hidden by the flap is from an article in Science by Fischer and colleagues in 1999.  The problem is that the axes are mislabeled in The Down-to-Earth Guide—the air temperature axis is labelled “Carbon dioxide concentration in the atmosphere” while the carbon dioxide axis is labelled “climate temperature”.  As the article in Science noted, “High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased…six hundred plus-or-minus four hundred years after the warming of the last three deglaciations.”  As Fischer and colleagues noted, air temperature leads; carbon dioxide follows.

After this mislabeling of axes was disclosed, Dr. Michael Oppenheimer of Princeton University weighed in on the issue.  He wrote,

“I have reviewed the figure on page 18 of The Down-to-Earth Guide to Global Warming. It appears that the labeling of the axes has been reversed. As a result, the curve labeled ‘carbon dioxide concentration’ should be labeled ‘climate temperature’, and vice versa.  However, the description of the figure in the accompanying text is accurate, and it fairly represents the current state of scientific knowledge, in terms that would be comprehensible to children 8-years of age or older.”  

Remember that the description of the figure is that “the more the carbon dioxide in the atmosphere, the higher the temperature climbed…the less carbon dioxide, the more the temperature fell…by connecting rising carbon dioxide to rising temperature[,] scientists have discovered the link between greenhouse-gas pollution and global warming.”  This is patently false and children aged 8 and older would easily be able to understand that.

In the intervening quarter-of-a-decade since Fischer and colleagues’ article in Science, research has confirmed that carbon dioxide follows and does not lead atmospheric air temperature.  A subsequent article in Science showed that carbon dioxide concentrations followed air temperature by a period of less than a thousand years while another article in Science concluded that “the carbon dioxide increase lagged Antarctic deglacial warming by 800 ± 200 years”.  Both are consistent with the original estimates by Fischer and colleagues.

In 2007, a review paper concluded that little evidence exists that greenhouse gases “have accounted for even as much as half of the reconstructed glacial-interglacial temperature changes.”  Yet another paper in Science that year wrote that the East Antarctica ice core “shows no indication that greenhouse gases have played a key role in such a coupling [with air temperature].”

A more recent study concluded that “changes in atmospheric carbon dioxide concentration did not cause temperature change in the ancient climate”.  In 2017, geochemist Euan Mearns commented that “It is quite clear from the data that carbon dioxide follows temperature with highly variable time lags depending on whether the climate is warming or cooling” and “carbon dioxide in the past played a negligible role [in determining temperature] … it simply responded to bio-geochemical processes caused by changing temperature and ice cover.”

Mearns’ comment is especially important when understanding why carbon dioxide responds to changes in air temperature.  During colder periods, oceans absorb more carbon dioxide due to the high solubility of carbon dioxide in cold ocean water at higher latitudes where sinking cold sea-water sequesters it in the deep ocean.  When the planet warms, oceans outgas this absorbed carbon dioxide back into the atmosphere.  Although plants grow faster in a warmer and more carbon-dioxide-rich environment, and thereby use more carbon dioxide, the ocean reservoir is about sixty-five times larger than that of the biosphere.

But what about changes in carbon dioxide on shorter time scales?  If changes in global air temperature drives changes in carbon dioxide on the century-to-millennial scale, could a change in carbon dioxide on a decadal-to-century scale affect global air temperatures?  

To answer this question, I would encourage you to read my chapter, Chapter 8, in Cal Beisner’s and my new book, Climate and Energy:  The Case for Realism by Regnery Publishing.  In that chapter, I outline that the first two-hundred-eighty parts per million of carbon dioxide, as well as all other greenhouse gases in the atmosphere, accounts for the absorption of about ninety percent of the thermal infrared radiation emitted by the Earth’s surface.  A doubling of carbon dioxide with no increase in the other greenhouse gases could at most absorb only an additional ten percent or only one-nineth of the amount currently absorbed by atmospheric gases.  But through numerical simulations, a doubling of carbon dioxide will cause the absorption of only about one-ninetieth of the amount absorbed by the first two-hundred-eighty parts per million.  That amounts to less than about one degree Celsius.

For more than a decade now, I and others have been arguing that carbon dioxide is not a magic climate change control knob.  Rather than being a pollutant in the planetary system, carbon dioxide is food for plants—simply put, they grow better and faster under enhanced carbon dioxide concentrations.  Thriving vegetation is good news for animal life and humans as well.  We must stop the demonization of carbon dioxide and embrace its effects as the whole biosphere benefits from the additional carbon dioxide.