Since Woodstock is going green with the efforts of the Green Team, I thought I would put in my own 2 cents on the subject of the impact of human activities on the environment. Yesterday, I drove behind a diesel truck spewing black exhaust and wondered why the driver was not arrested. I have to confess that I have little expertise in this complex field. There’s no question in my mind that conservation of the environment through reduction of fossil fuel combustion is inherently good; the guy who picks up roadside trash is also inherently good; and then there is Al Gore who, after inventing the Internet ;-) , took a revolutionary step in promoting environmentalism. All of this is good. It would be nice to know as much as possible about the potential impact of man’s pollution of the Earth so this can be addressed most effectively. John

The carbon that enters the global carbon cycle due to fossil fuel combustion (human activity) is estimated at 5.5 gigatons of carbon per year. Contribution of humans to the carbon cycle, often referred to as “anthropogenic” carbon flux, is mostly due to burning of fossil fuels, cement production, and alteration of land use. The 5.5 gigaton/yr of carbon (GtC) figure is widely accepted among environmentalists (NASA (2008) http://earthobservatory.nasa.gov/Features/CarbonCycle/carbon_cycle4.php ). 

Figure 1 below is one of many diagrams that can be found on the Internet from authoritative sources all of which say basically the same thing. I chose this schematic because it is easier to read; but wherever one looks the quantities of carbon in storage reservoirs and fluxes are more or less the same (therefore, there is no controversy in these numbers).  The numbers in black in Figure 1 are GtC in storage reservoirs and the numbers in purple represent the amount of carbon (GtC) in fluxes between the source of emissions and the reservoirs (atmosphere, surfaces of oceans, deep oceans, vegetation, soils, sediments and unspent fossil fuels, etc.).

Figure 1: The global carbon cycle

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[Source: http://www.global-greenhouse-warming.com/global-carbon-cycle.html ]

But controversy arises when one tries to determine the impact of anthropogenic carbon flux on the environment. Charles Keeling states “Although the pathways of carbon through the global carbon cycle are understood in general, knowledge of the actual rates of change of the fluxes between the atmosphere, land, and ocean is less advanced. The annual anthropogenic carbon input to the atmosphere between 1980 and 1989 has been estimated to include 5.5 +/-0.5 GtC (thousand million metric tons of carbon) from fossil fuel combustion and 1.6 +/- 0.6 GtC from  land-use change, yielding a total of 7.1 +/- 1.1 GtC. Of this annual input, 3.3 +/- 0.2 GtC remained in the atmosphere, and 3.8 GtC were removed. Oceanic uptake, related to carbonate buffering, is thought to account annually for about half of the removal. Re-growth of northern hemisphere forests has been estimated to account for perhaps 0.5 +/-0.5 GtC. The removal mechanisms of the remaining carbon, 1.3 +/-1.5 GtC per year, are uncertain (Proceedings of the National Academy of Science 94:8273-8274, 1997; http://books.nap.edu/openbook.php?record_id=6238&page=1#p200032759970001001 )”.

Examination of mathematical calculations that attempt to measure the dynamics of the global carbon cycle reveals a very complex situation that is not fully understood (Bjorkstrom “A Model of CO2 Interation between Atmosphere, Oceans, and Land Biota” ; http://www.icsu-scope.org/downloadpubs/scope13/chapter15.html ).

Canadell et al (“Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks” Proceedings of the National Academy of Science 107(47):18866-18870, 2007; http://www.pnas.org/content/104/47/18866.full ) states that growth of atmospheric CO2 is the largest human contributor to the global carbon cycle and human induced climate change (because it’s a greenhouse gas), and that rate of fossil fuel CO2 emissions rose from 1.3% per year to 3.3% per year comparing the 1990’s with 2000-2006. This rate of change takes into account the balance between anthropogenic carbon emissions and the natural processes that remove CO2 from the atmosphere such as vegetative photosynthesis and ocean processes summarized in Figure 1.

As an aside, given the world’s population of 6,781,243,583 (as of September 1, 2009; http://www.census.gov/ipc/www/popclockworld.html) one might think that humans contribute to atmospheric CO2 emissions just by breathing. Since the atmospheric CO2 concentration is 0.04% and exhaled breath averages 4.4%, I conducted a quick calculation based on a human exhaling 432 liters CO2 per day (the higher estimate) or 157,680 per year or 9.46 x 1014 liters for 6 billion humans per year. If there is 1 x 1022 liters of air around the earth (normalized to ground level atmospheric pressure) then 4 x 1019 liters of CO2 in the atmosphere or 0.002365% is exchanged between humans and the atmosphere in a year or 0.00000648% per day. So, the contribution of human respiration to the global carbon cycle appears to be insignificant compared to CO2 produced from industrial sources.

Figure 2 (below) shows that the more industrialized countries contribute to most of the CO2 emissions. This figure gives the ranges of CO2 emissions by country in “thousands of metric tons” annually; thus, the USA is responsible for emissions of 5,752,289,000 metric tons per year.

Figure 2: CO2 emissions by country.

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[source: http://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_emissions ]

I hesitated to include Figure 3 which appeared in the New Scientist in February 2005 because I can’t validate this data (http://www.newscientist.com/article/mg18524861.400/2-climate-change-menace-or-myth.html ).  The cautious caption with this figure is as follows “Global warming is a fantasy dreamed up by climate scientists, say the skeptics. Could they possibly be right?” asks Fred Pearce the author. Figure 3 represents the only example that I could find where global temperatures, which are directly linked to CO2 emissions, are plotted plus or minus human activity on the earth. This figure suggests that without human activity, the globe would be cooling rather than warming.

Figure 3: Global warming due to human activity.

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