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Timothy Casey B.Sc.(Hons.): Consulting Geologist   


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Deforestation & Carbon Emission

Abstract

This article explores the reasons for the observed increase in very recent atmospheric carbon dioxide concentration. The fall of atmospheric carbon dioxide over the last half billion years and the very recent inverse correlation of atmospheric oxygen response support the well documented growth response of plants to elevated carbon dioxide. This confirms a dynamic equilibrium that adjusts the uptake of carbon sinks in response to carbon dioxide availability, and suggests that the increase of atmospheric carbon dioxide requires more than a minor rise in carbon dioxide input. Reduction of photosynthesising biomass through indiscriminate deforestation constitutes damage to the self-regulating mechanism that removes carbon dioxide from the atmosphere and a review of the evidence shows that the yearly deficit in photosynthetic uptake of atmospheric carbon dwarfs the carbon emission of fossil fuel combustion.

 

The "Rise" of Atmospheric Carbon Dioxide

Present atmospheric carbon dioxide concentrations are not unprecedented in geological history. Throughout the Phanerozoic spanning the past 600 million years, carbon dioxide concentrations have been sporadically falling from well above 6000ppm (Berner, 2001). Carbon dioxide has risen before, only to be sequestered in its unstoppable decline to an all time low of 200ppm - in the midst of human history.

Graph of carbon dioxide concentrations falling from about 7000ppm circa 530mya to 
300ppm about 300mya, rising to 2500ppm about 160mya and falling as low as 200ppm in the last ice age. Carbon dioxide after Berner (2001) & temperature after Scotese (2001; see also Boucot et al., 2004) sourced from www.geocraft.com showing the degree of variation in carbon dioxide throughout geological history.

Although industrialisation began at a similar time to the most recent rise in carbon dioxide levels, such rises also have natural causes as they are not unprecedented. Furthermore, surges in carbon dioxide emissions such as the post World War II automobile boom did not affect the rate of atmospheric carbon dioxide accumulation. However, what is most apparent in the trend of atmospheric carbon dioxide concentration over the past half billion years is that it has been steadily consumed and predominantly by photosynthesis. It is evident from previous atmospheric carbon dioxide concentrations vastly exceeding current levels that the increase in atmospheric carbon dioxide may not be caused by the degree of carbon dioxide input but instead by the degree of carbon dioxide consumption.

 

Carbon Dioxide & Oxygen Equilibrium

Oxygen is almost exclusively the product of photosynthesis (Lyons, 2007), and as one of the precursor chemicals of this process is carbon dioxide, we can expect an inverse correlation between the atmospheric oxygen curve and the carbon dioxide curve through time in absence of other processes affecting carbon dioxide and oxygen levels. This is in fact observed by Keeling et al. (1996) in measurements taken last century.

Although recent media attention has focussed on the claim that increasing atmospheric carbon dioxide introduces inefficiencies to the process of photosynthesis, it is widely known as a matter of verifiable fact that increasing atmospheric carbon dioxide drastically increases plant growth. Plant growth not only depends on the photosynthesis of carbon dioxide but also increases the photosynthesising infrastructure. This is supported by studies of past growth (Waddell et al., 1987; Graybill & Idso, 1993; Grace et al., 1995; Smith et al. 2002). It is also supported by experimental results (Idso & Kimball, 1991; Idso & Idso, 1994; Idso & Kimball, 1994; Kimball et al., 1995; Pinter et al., 1996; Idso & Kimball, 1997; Kimball et al., 2007). Carbon dioxide also drastically accelerates reproduction of algae (Shapiro, 1973) and plankton (Riebesell, 1993).

The sum of this research is that the photosynthesising biomass of planet Earth adjusts its growth to best exploit available atmospheric carbon dioxide. Thus any increase in carbon dioxide emission by human beings, fossil fuel combustion, volcanoes, or any other cause in absence of factors affecting the mechanism of photosynthetic carbon sequestration, is easily absorbed by the planet's photosynthesising biomass. This indicates that the increase in atmospheric carbon dioxide concentration is not controlled by any carbon dioxide emission, but by the reduction of natural carbon sequestration infrastructure such as photosynthesising biomass. Deforestation is the most direct and prolific anthropogenic reduction of a natural self-regulating carbon sink.

 

The Impact of Deforestation

Deforestation & Aridity

The link between deforestation and aridity is well documented. Aridity in Australia's Mallee region is a text-book example of the consequences of excessive land clearance (White, 1994). Forests produce a substantial amount of water vapour, which contributes to precipitation and apparently to tropical glaciers. Mount Kilimanjaro glacial retreat is popularly blamed on global warming, however according to Kaser (2004) it is aridity and not warming that is the problem - as confirmed by the formation of penitentes; ablation structures on the surface of the glacier. The loss of aspired moisture from forests cleared around the foothills of Kilimanjaro dried the air flowing over the glacier. Dry airflow causes sublimation of ice (as opposed to melting) and resulted in the retreat of the ice (Mason, 2003).

In spite of Mason (2003) & Kaser (2004), which so well document this drastic example of how deforestation affects the environment, Gore (2006), some two years after these publications still insisted that the Kilimanjaro glacial retreat was caused by global warming, never mind the presence of penitentes confirm that aridity and not temperature was the mechanism. Of notable coincidence, the Mason (2003) reference is buried behind the "premium content" blind of http://nature.com without so much as a volume, page number, or abstract available to the visiting public.

 

Deforestation & Carbon Emissions due to Deflation

Eswaran et al. (1993) determined that 1576 gigaton of carbon is stored in soils. Desertification resulting from deforestation is characterised by dust storms during which the soil is blown away on the wind. Eswaran et al. (1993) estimate that loss of soil carbon due to erosion resulting from these processes is about 20-50% in previously forested regions. The work of Eswaran et al. (1993) demonstrates the large amount of carbon that can find its way into the atmosphere through the process of desertification. Atmospheric carbon from land deflation as a long term consequence of deforestation is a matter of ongoing enquiry.

Weathering of rocks into soil is a another major sink for carbon dioxide as carbon dioxide is combined into soil carbonates when sufficient moisture is present. Thus, the ability of soil formation to act as a carbon sink depends a great deal on the presence of vegetation. It is important to note that soil deflation represents a reduction of natural carbon sequestration infrastructure that is separate and distinct from vegetation.

 

Deforestation & the Carbon Budget

It is known that photosynthesis consumes about 120 gigatons of atmospheric carbon in the form of carbon dioxide, every year (Bowes, 1991). However, this is only after extensive deforestation. The one question not addressed by "environmental" lobby groups concerns the impact of deforestation on global photosynthesis; IE the ongoing impact of reducing photosynthetic biomass from the carbon budget.

Photosynthesising biota represent a pool of around 560 gigatons of carbon (Schlesinger, 1991). 156 gigatons of carbon were released to the atmosphere as a result of land clearance between 1850 and 2000 (Haughton & Hackler, 2002). Although this refers to the one-off average of combustion and decay of cellulose, it also presents us with a conservative estimate of the proportion of photosynthesising biota removed from the biosphere. Given the current rate of carbon emission due to modern land clearance processes of 2.3 gigatons per annum (Haughton & Hackler, 2002) this would leave about 540 gigatons of carbon pooled in photosynthesising biota at the turn of the century.  The carbon pooled by photosynthesising biota in 1850 would have been closer to 696 gigatons, and thus deforestation represents the removal of 22% of photosynthesis from the carbon budget since 1850.

Given this reduction, the current rate of photosynthetic sequestration of carbon at 120 gigatons of carbon per year (Bolin et al., 2000; Gifford 1982), would have had to have decreased from 154 gigatons of annual photosynthetic sequestration of atmospheric carbon in 1850. The ongoing impact of cumulative photosynthesis reduction from 1850 to the turn of the century is 34 gigatons of unsequestered carbon with a cumulative acceleration averaging 0.2 gigatons per annum for every year of deforestation from 1850 to 2000 but at modern rates (after 2000), this figure would be closer to 0.5 gigatons of carbon per annum for every year of deforestation. The 2008 photosynthetic carbon deficit due to deforestation is 38 gigatons of atmospheric carbon, or 140 gigatons of carbon dioxide (for those wanting a comparison with IPCC, 2007).

 

Conclusion

Carbon emissions due to fossil fuel combustion represent less than 20% of the total human impact on atmospheric carbon levels. Deforestation not only contributes a relatively minor one off carbon emission of some 2.3 gigatons of carbon to the atmosphere, but an ongoing loss of photosynthetic carbon sequestration to around 38 gigatons per annum that is growing at the rate of 500 megatons every year. It is clear from the fact that this amount dwarfs the present 7.8 gigaton fossil fuel combustion contribution (IPCC, 2007), that the cessation of fossil fuel combustion will not halt the rise of atmospheric carbon dioxide because the loss of photosynthesising biota and the corresponding fall in photosynthesis is so much greater. The current focus on fossil fuel combustion to the exclusion of ongoing impacts of deforestation only serves to blind the public to the consequences of excessive land clearance and the fact that deforestation and consequent soil deflation are the simplest explanation for the unprecedented rise in global aridity during a warming phase.

Replanting of forests and reclamation of land for jungles, woodlands, and sustainable forestry industry must be given first priority if the human impact on atmospheric carbon dioxide accumulation is to be brought under control. More importantly, deforestation causes the expansion of arid regions and this fact is well demonstrated by the human history of Australian environment (White, 1994). If we are to protect our agriculture, we must moderate its extent and use well diversified woodlands for both soil conservation, symbiont harvesting (eg. truffles), and sustainable forestry.

 

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