The Little Things that Change the World, part 2

As if brandishing a snowball on the floor of the US Senate wasn’t enough to demonstrate a lack of understanding of basic science, let alone climate science, Senator James Inhofe is set to travel to Paris in December taking with him the message Republicans intend to unilaterally sabotage any agreement the world comes to for dealing with human-induced climate change.  While the snowball stunt exposes a fundamental misconception about winter and the affect of Earth’s axial tilt, the overall denial of humankind’s ability to impact the global system is ignoring the history of the Earth.  A history readable in the geologic record.

In part one, we examined the impact the innovation of photosynthesis in single-celled organisms had on the Earth during the Precambrian, an impact absolutely essential for the evolution of multicellular life, including that of a bipedal, large brained species of primate we know as Homo sapiens.  In this installment, let’s take a look at what happened during the middle Paleozoic.

The record of atmospheric composition in the Precambrian indicates few large scale changes in the amount of oxygen and methane.  Carbon dioxide does seem to exhibit a steady downwards trend until a couple of upward curves towards the end of the Era.  In contrast, the Paleozoic Era displays significant fluctuations in both the oxygen and carbon dioxide concentrations.  See the graph in part one.  Focusing in more closely on the Paleozoic and up to the present, one can notice some significant trends:

Changes in atmospheric oxygen and carbon dioxide since the end of the Precambrian. Image: Dorell and Smith, 2011; ec.asm.org

There is a direct relationship between the evolution of life, its distribution on Earth, and the concentration of oxygen and carbon dioxide in the atmosphere.  The inverse relationship between the increase of oxygen/decrease of carbon dioxide is likewise directly related to the prevalence and distribution of life.  It is important to remind ourselves of the general difference between plants and animals.  Plants tend to take in carbon dioxide, and give off oxygen.  Animals, on the other hand take in oxygen and give off carbon dioxide.  The interplay between plants and animals, and their relative abundances influences the overall composition of the atmosphere.

A few points in time indicated by arrows at the bottom of the chart are particularly noteworthy: early land plants (embryophytes) made their appearance at point 0; vascular plants first appeared at point 2; conifers at point 3; and flowering plants at point 4.  The lettered arrows are related to events having to do with the lineage of algae.  At each of the points, particularly those in the middle-Paleozoic, an abrupt decrease in carbon dioxide is coincidental with an important event related to the evolution and distribution of plants.  The innovations allowed the plants to take advantage of empty niches, rapidly spreading across the Earth.  The sheer volume of trees and other plants depleted the atmosphere of carbon dioxide, at the same time as enriching it in oxygen.  The Carboniferous Period is aptly named, as the vast forests eventually became the extensive coal beds we mine today to fuel an industrialized society.

At the same time, particularly in the Devonian and early Carboniferous (I learned it as the Mississippian Period), extensive reefs in the shallow seas surrounding continents and islands were built.  The primary builders of these reefs were corals, animals with a calcium carbonate (CaCO₃) exoskeleton.  These coral reefs therefore also became vast storehouses for sequestered carbon dioxide as the corals extracted it from the oceans to build their skeletons.

This uptake of carbon dioxide into the structures of plants on the land, and corals in the sea, resulted in a significant decrease in the amount of carbon dioxide in the atmosphere.  All of that formerly atmospheric carbon dioxide was sequestered in the rocks!  And it is a tremendously large amount of carbon dioxide, in rocks from tens of millions of years of plants living and dying, reefs getting built and buried.

The implications for our modern society relate to both reservoirs of fossilized carbon dioxide.  Humans are actively mining the old Paleozoic forests we now find as coal beds.  Those 300 million year old trees (along with younger coal beds from the Cretaceous and Tertiary Periods) are burning in power plants in countries around the world, returning the sequestered carbon dioxide to the atmosphere.  When this carbon dioxide, as well as the small amounts of sulfur dioxide formed when the sulfur in the coal burns, combine with water in the atmosphere, and in surface waters it forms mild solutions of carbonic acid and/or sulfuric acid.  Falling on the fossilized reefs exposed on land, and in contact with active reefs in the ocean, the acid reacts with the calcium carbonate, liberating small amounts of carbon dioxide.  This is on top of the impact of more acidic ocean water on the ability of reefs to survive, a topic for another day.

Returning to our original premise and Sen. Inhofe’s statement humans are incapable of impacting Earth’s climate.  Trees and corals, organisms of lesser status in Inhofe’s worldview, had a tremendous impact on Earth’s climate, causing changes taking place over several hundreds of millions of years.  And now in our modern age, we are taking the records of those many years and exposing and dissociating them in a time 0.0000005 as long as it took those deposits to form.

It does not take a scientist to understand the implications of releasing over 200,000,000 years of carbon dioxide sequestration in 100 years.  Today is Thanksgiving, a day given to overindulging, eating several days worth of calories in a single meal.  Now imagine all the Thanksgiving meals you have ever eaten and put them on the table before you.  Eat them all, today.  The analogy is apt, as our modern society overindulges without thought for the consequences of figuratively eating tens of millions years worth of carbon in a single day.  We are treating the Earth and its climate as if we were consuming all those meals in a single day, rather than spread out over a lifetime.  It is past time to get off our addiction to fossil fuels, to go on a diet through enacting sensible regulations to limit future emissions of carbon dioxide into the atmosphere.  We just might have something left for the future.