1. Are carbon dioxide levels in the atmosphere increasing?

2. Do Americans produce a significant amount of carbon dioxide?

3. Does deforestation increase the amount of atmospheric carbon dioxide?

4. What sources might you use to find the best data to answer these questions? On what data can your conclusion be based? What measurements could be used to obtain the answers?


Carbon is continually recycled through what is known as the carbon cycle. Plants convert carbon dioxide into organic matter. When animals eat plants, or when decomposers break down dead plants or animals, the carbon in organic matter is converted to carbon dioxide once again.
Does all of this organic matter get recycled? No. Think of a swamp for a minute. Every year, new organic matter ends up at the bottom of the swamp. Not all of it returns to carbon dioxide of the air-every year the "muck" just gets thicker and thicker. For hundreds of millions of years, living things have been buried before their organic molecules could be decomposed. The remains of countless living things of the past were compressed over long periods of time to produce petroleum and coal. Coal and the derivatives of petroleum (gasoline, kerosene, propane, methane) are carbon-based molecules, just as were the organic molecules from which they were produced. In the following drawings, black dots represent carbon atoms and red dots represent hydrogen atoms.

carbon molecules

Over hundreds of millions of years, carbon atoms were taken from the air and were buried deep underground. Humans are changing that. Our energy needs drive us to dig and drill for this ancient coal, oil, and natural gas. When we burn these fossil fuels for energy (as in the combustion of two octane molecules in gasoline depicted below), the fossil fuels react with oxygen to form water and carbon dioxide. The combustion of fuel puts additional carbon dioxide into the air. The tar in the following picture is a petroleum derivative; this carbon has been buried for millions of years.


Enormous amounts of carbon are stored in coal, oil, and natural gas. A gigaton of carbon is equal to about 2200 billion pounds. There is more carbon stored in fossil fuels than in the atmosphere, forests, soils, and surface ocean combined.


Burning fossil fuels create carbon dioxide.

formation of carbon dioxide

Carbon dioxide emissions are rising. Human activity is currently releasing an excess of 6-7 billion metric tons of C/year to the atmosphere which results in about a 3 billion ton/year gain in the atmosphere. Seventy percent of the global emissions of carbon dioxide results from fossil fuel use (WHO 1990a) although some results from deforestation (1-2 billion tons). Coal and oil currently contribute equal amounts of carbon into the atmosphere. Since world coal reserves are so much greater than world oil reserves, the percentage of carbon dioxide produced by coal emissions will probably increase. The average car releases 5 tons of carbon dioxide into the atmosphere per year.

Globally, humanity is releasing more carbon dioxide than in the past. Since the beginning of the Industrial Revolution, CO2 levels have risen 25%. From 1860 to the present, CO2 concentration in the air has risen from 290 ppm (parts per million) to 350 ppm and is currently increasing at 1.5 ppm/yr. The amount of carbon dioxide released through human activity increased from 32 million tons/yr in the 1800s to 3.4 billion tons a year in the early 1900s. From the period of 1945 to the oil crisis in 1973 (at which point emissions were at 18.6 billion tons/yr), carbon dioxide emissions increased 5% a year (Bowen, 2005). Obviously, as the global population increases, so will its production of carbon dioxide. For each 1% increase in global population, carbon dioxide output increases 1.4%. This population driven increase in carbon dioxide output is greatest in developing countries (Shi, 2003). Since 1980, the carbon emissions of China have increased 80%. Humanity is currently burning four times the amount of fossil fuel used in 1950. The past and current generation are estimated to have contributed two thirds of the carbon dioxide responsible for modern climate change (Friedlingstein, 2005).


--after Kemp, 2004


2) America's Carbon Dioxide Production
America produces a disproportionate amount of carbon dioxide emissions. The average American releases 5 tons of carbon into the air per year. The average car releases 5 tons of carbon into the air per year. The United States produced 32% of the world's carbon dioxide during the period of 1950 to 2000 with an estimated total of 182 billion tons (Blatt, 2005). The amount of greenhouse gas emissions in the U.S. (with its 260 million people) is equivalent to those of 2.6 billion people living in more than 150 countries (Speth, 2004). The amount of carbon dioxide release from fossil fuel use in America increased more than 17% from 1990 to 2000 (U.S. Greenhouse Gas Inventory Program, 2002). There is a plant which generates electricity in Ohio which burns 7.5 million tons of coal a year and produces almost as much carbon dioxide as the entire world produced in the year 1800 (Bowen, 2005). Although the Unites States only composes 5% of the world's population, we use 25% of the world's energy.



--after Raven, 2001

3) Deforestation

The burning of forests returns carbon into the air and the cropland and grassland which typically replace the lost forests only absorb 20% the CO2 that is absorb by the forest. For example, the following first photo depicts land which was once covered in the type of subtropical rainforest depicted in the second photo. Given that plants absorb carbon dioxide out of the air to grow, how would deforestation affect the amount of carbon an area of land could hold?


1. How would you view America's carbon dioxide emissions if you lived outside the United States?

2. When you consider the gasoline which moves your car, the fossil fuels which produce the electricity you use, and the deforestation which is needed to support the plants and animals you use for food, how much carbon dioxide in the atmosphere are you responsible for? How does your production of carbon dioxide compare to that of people who live in other parts of the world?