Carbon is continually recycled through what is known as the carbon cycle. Plants convert carbon dioxide into organic matter. When animals eat plants and perform respiration to obtain energy 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.
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 originated in ancient living things and had been buried for millions of years.
chart on carbon resevoirs
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. (The deep ocean contains almost 8 times more carbon than stored in fossil fuels.) If all of fossil fuels were used, the global temperature would rise between 4.5 and 15oC which is warmer than the planet has been in the past 200 million years. One gallon of gas (which includes molecules of octane whose combustion is depicted below) weighs 7 pounds and produces 22 pounds of carbon dioxide (Bowen, 2005).

gas burning
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. 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.

What are the effects of putting additional carbon dioxide molecules into the air?
Globally, humanity is releasing more carbon dioxide than in the past. Since the beginning of the Industrial Revolution, CO2 levels have risen 25%. In 2005, the concentration of carbon dioxide in the atmosphere was 379 parts per million which is significantly more than the amount prior to the preindustrial value of 280 ppm or the range during the last 650,000 years of 180-300 ppm (IPCC, Document I, 2007). . 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). Eight gigatons of carbon are being added to the year each year.  If growth continues along its current path, this value will grow to 10 gigatons by 2025 and 15 by 2050 (Matthews, 2008). 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). Regarding the total amount of emissions, the greatest amount of heat-trapping gases was released in the year 2004 (Union of Concerned Scientists, 2007).Those who live in cities are, on average, richer than those who live in rural areas; they also use more consumer goods and produce more trash and greenhouse gases (Normille, 2008). China and the US are about equal in the amount of carbon dioxide they produce and China will soon surpass the US in this category (Normille, 2008).

America produces a disproportionate amount of carbon dioxide emissions. The average American releases more than 5 tons of carbon into the air per year (about 5.37 tons), making America the highest per capita emitter in the world. 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. In 2004, the U.S. used 20 billion barrels of petroleum, of which 13 billion were required for transportation (Lattin, 2007).

--after Kemp, 2004

--after Raven, 2001

Of the global population, the billion people who live in the most developed countries use about half the global energy supply while the billion people who live in the least developed countries use only 4% of the global energy supply (IPCC, Document III, 2007). The following comparisons of per capita carbon emissions are drawn from the United Nations report on Population growth in 2005.



Coal provides 60% of the energy used in China and China’s oil demand is second only to that of the United States (Soytas, 2006).

Between 1950 and 1997, the number of cars in the world increased from 50 million to 580 million. In China, the number of cars has increased from 2.1 million in 2001 to 7.2 million in 2006. Passenger air travel is growing at 5% per year, faster than any other form of transportation. Not only have the number of personal vehicles greatly increased, but the weight and speed have increased at the expense of fuel economy. If the vehicles of the U.S. had remained comparable to the 1987 standard in weight and performance, modern fuel economy would be 24% greater than it is. Instead, the increase in vehicle weight (27%) and time required to increase speed from 0 to 60 mph (30%) has increased fuel consumption. A 10% weight reduction could decrease fuel consumption by 4-8%. In the U.S. and Japan, vehicle weight has increased 10-20% in the past 10 years (IPCC, Document III, 2007). The increase in the energy required for transport is expected to grow at 2% per year (with most of the increase in developing nations) and result in an 80% increase by the year 2030 (IPCC, Document III, 2007).

Greenhouse gas emissions are currently increasing at a rate of 1.6% per year and the emissions released from fossil fuel consumption are increasing at 1.9% per year. The rate of increase after the year 2000 has been higher than that of the 1990s. Greenhouse gas emissions have increased 70% since 1970. Unless serious efforts to reduce emissions are enacted, emissions are expected to rise by 50% by the year 2030. Since the mid-1800s, fossil fuel consumption has released about 1100 gigatons of carbon dioxide into the atmosphere (IPCC, Document III, 2007).

One of the strategies to combat global warming which is being researched is that of carbon sequestration in which large quantities of carbon could somehow be stored in a form which would not affect levels of atmospheric carbon dioxide. Carbon sequestration could be accomplished by pumping carbon dioxide into strata of impermeable rock. Another technique could be to convert carbon from biomass into black, solid carbon and incorporate it into soil. Many soils already have high values of black carbon in them without ill effects (Fowles, 2007).

The planet has gotten warmer in recent decades. Average global temperature increased 0.6 degrees Celsius in the 1900s. One third of this change occurred in the period from 1990 to 2000 (IPCC, 2001). The 24 warmest years since 1900 have all occurred since 1973. Nineteen of the twenty warmest years have occurred since 1980. The ten warmest years have all occurred since 1990 with 1998 and 2005 being tied for the hottest year on record. In the Northern Hemisphere, 2005 was the hottest year on record (Union of Concerned Scientists, 2007; Blatt, 2005; Nordell, 2003; Liu, 2005; Patz, 2002). Prior to 1990, the 1980s was the warmest decade on record. The temperature of wells in Northern Canada has increased about 2 degrees Celsius (Majorowicz, 2004). The average temperature in Antarctica has increased 5oF since 1945 (Blatt, 2005). The years 2005 and 1998 are the two warmest years on record (IPCC, Document I, 2007).
Global temperature is predicted to increase throughout the 21st century. Global warming models predict that the climate will warm at a rate of .15 degrees or more per decade over the next several decades (Hansen, 2001; WHO, 1990a) It is currently estimated that the average global temperature will increase by 1.4 to 5.8 degrees Celsius by the end of the 21st century (IPCC, 2001; Huntington, 2003). By the end of the 21st century, the global temperature will be higher and increasing more quickly than at any time in the past 140,000 years (Last, 1993).


--after Kemp, 2004

Between 1961 and 2003, the oceans have warmed about 0.1 degree Celsius.

If emission regulations could result in a peak of emissions in the next 15 years followed by a 50% reduction by the year 2050, the global temperature rise could be limited to 2.8 to 3.2 oC above the level prior to the Industrial Revolution. If delays in implementation do not peak emissions in the next 15 years, global temperature rise will be greater (IPCC, Document III, 2007).