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Vol. 18 No. 1 - January 2012

Earth's Dynamic History of CO2
A Fascinating and Surprising Tale

 By: Anjum Farooqui*

There is an old saying; “The Whole is greater than the sum of the parts”. We cannot have complete faith in the ability of any computer models to predict future behavior of any natural system - especially a system as complex as that for the whole planet! So we have a lot more to learn and to study about complexity of ecosystems, climate, and their computer models before we get too emotional about the “Greenhouse effect. Any type of system from the micro- atoms to the macro- galaxies in the Universe are self-organizing and self-regulating, relating to one another, where we can find clues of the past events inscribed on the stones as fossils or in other natural archives. This enlightens us about the future patterns and predictability of global climatic change. Scientists have enormous data which enable us to identify and have a better understanding of the present and possible future global weather by looking at the planet's weather through geological time.

There are several scars of cataclysmic events that our planet Earth has experienced in the past before man arrived. No doubt man has evolved our planet into the present Eden where only handful of population is concerned for it and the rest are busy enjoying the heavenly gifts on this Earth. The several jolts to the Earth in the past have removed 90% of the species that have ever existed. It is very hard to say about the precise reason which was responsible to set the catastrophic events but surely created a disbalance in the level of the carbon dioxide content in the air throughout the Earth’s geologic time. Long-term reconstructions of atmospheric CO2 levels going back in time show that 500 million years ago atmospheric CO2 was some 20 times higher than present values. Some 200 million years ago this level dropped and then rose to 4-5 times of present levels--a period that saw the rise of giant fern forests--and then continued a slow decline until recent pre-industrial time. Carbon dioxide (CO2) forms approximately 0.04% of the Earth’s atmosphere. It is essential for photosynthesis in plants and other photoautotrophs, and is also a prominent greenhouse gas.

Global carbon dioxide emissions

Carbon dioxide is released to the atmosphere by a variety of natural sources, and over 95% of total CO2 emissions would occur even if humans were not present on Earth. For example, the natural decay of organic matter in forests and grasslands, such as dead trees, results in the release of about 220 gigatonnes of carbon dioxide every year. This carbon dioxide alone is over 8 times the amount emitted by humans. The increasing measured fraction of CO2 in the atmosphere over the last 100 years implies that the level of equilibrium between sources and sinks of CO2 is rising. Biological consequences of earth’s climatic change through geological periods (macro change) - the age of fishes, age of amphibians, age of reptiles - resulted in high magnitude changes and widespread extinctions (with some carry over remnants). These catastrophic events caused populations of individual species to shrink or expand inducing changes in the food chain and creating ripple effect in an ecosystem which is called 'tropic cascading'.

Relationships between the Ocean and Carbon:

Oceans are the 'Carbon Bank' where most of the Earth's carbon including CO2 is stored. It has been that way for millions of years with contributions of both organic and inorganic sources in the oceans, from the atmospheric gas exchanges, and from fluvial sources through rivers and other erosion methods on land of terrestrial organic and inorganic materials. Tectonic movement and undersea volcanic action also release CO2 to the atmosphere in varying amounts so that there has been periods during the earth's geological time scale when the ocean released more CO2 into the atmosphere than it removed. The removal and storage of atmospheric CO2 by the oceans is done by biological means involving the total oceanic food chain (waste materials and dead organisms accumulating on the ocean floor) and the structural recruitment by calcifying organisms (coral reefs and limestone beds built up by corals, coraline algae, and other plants). Presently the ocean releases less CO2 back into the atmosphere than it removes during the 'carbon cycle' because it 'locks' a percentage of the CO2 into limestone and ocean floor sediments. The CO2 rises to the ocean's surface for atmospheric exchange through geochemical methods such as tectonic and volcanic activity, up wellings of deep ocean currents bring dissolved sediments to the surface and limestone erosion.

Man, Climate & the Carbon dioxide

Man's ancestors appeared at least 2 million years ago. There has been no perceptible change in man's physiology in 40,000 years - so why didn't agriculture and civilization begin 40,000 years ago? The Earth's climate was very erratic (during this 40,000 year period) up to 10,000 years ago - when the last ice age ended. After that last ice age (10,000 years ago) the weather went from erratic (normal) to stable (abnormal) and helped foster the birth of civilization through predictable climate (regular seasonal cycles of temperature change and wet/dry periods) best described as the 'steady-state environment'. This abnormal 'Steady-State' climate has made possible the progression of agriculture, which resulted in stable human societies and a greatly accelerated growth in the human population. Over the past 50 years, man's effect on Earth has been very detrimental, directly and indirectly - due to the huge growth in man's population and technology. We have the knowledge to reverse the negative impact we have made on reefs and oceans. We have the knowledge to reduce CO2 in the atmosphere by reduction of emissions and enhancement of biological fixing (capture) methods. It is just a matter of time and the Earth's 'hot-cold' and 'wet-dry' macro-climatic cycles will take us out of the present 'steady-state' environment we have experienced over this short geological period of the past 10,000 years.

Similarities with our Present World Average global temperatures in the Early Carboniferous Period were hot- approximately 20° C (68° F). However, cooling during the Middle Carboniferous reduced average global temperatures to about 12° C (54° F). Similarly, atmospheric concentrations of carbon dioxide (CO2) in the Early Carboniferous Period were approximately 1500 ppm (parts per million), but by the Middle Carboniferous had declined to about 350 ppm -- comparable to average CO2 concentrations today!

Earth's atmosphere today contains about 380 ppm CO2 (0.038%). Compared to former geologic times, our present atmosphere, like the Late Carboniferous atmosphere, is CO2 impoverished! In the last 600 million years of Earth's history only the Carboniferous Period and our present age, the Quaternary Period, have witnessed CO2 levels less than 400 ppm. There has historically been much more CO2 in our atmosphere than which exists today. For example, during the Jurassic Period (200 mya), average CO2 concentrations were about 1800 ppm or about 4.7 times higher than today. The highest concentrations of CO2 during all of the Paleozoic Era occurred during the Cambrian Period, nearly 7000 ppm -- about 18 times higher than today.

The Carboniferous Period and the Ordovician Period were the only geological periods during the Paleozoic Era when global temperatures were as low as they are today. To the consternation of global warming proponents, the Late Ordovician Period was also an Ice Age while at the same time CO2 concentrations then were nearly 12 times higher than today-- 4400 ppm. According to greenhouse theory, Earth should have been exceedingly hot. Instead, global temperatures were no warmer than today. Clearly, other factors besides atmospheric carbon influence earth temperatures and global warming.

Scientists are busy developing future technology that may greatly be important to our adaptation to climatic change rather than its prevention. These survival technologies to adapt to climatic changes will help the present day species to sustain on this changing earth and would put a strong option before mankind to accommodate in Mars and other planets with the advance technology for sustenance.

*Birbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow (India), <[email protected]>

This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.

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