Fossil Fuel Emissions and Atmospheric Carbon Dioxide
Editor’s note: This article is the first in a three-part series that investigates the connections among increasing atmospheric carbon dioxide concentrations, the ocean’s role in absorbing carbon dioxide and the effect on marine ecosystems, and what happens to atmospheric oxygen levels when the base of the food chain—phytoplankton—dies off.
Humans have used energy ever since lighting the first fire back in prehistoric times. As we progressed along with our technology, our need for more energy-intensive fuels grew.
The wood, whale oil and water wheels early settlers used in the United States did not provide enough energy to support the Industrial Revolution. In the 1800s, oil and natural gas were discovered and coal became the major source of energy for the nation, powering trains and factories. With the popularization of the car in the 1900s, people considered emissions of automobiles preferable to those of horses.
As industry and transportation expanded, emissions from fossil fuels began to present a problem. The pollution in heavily industrialized parts of the U.S. and Europe, described by some as the “smell of progress” in the air, was taking a toll on the health of citizens. This problem was somewhat remedied by building higher smoke stacks that allowed faster winds to carry pollution farther from the source. At the time, no one could have guessed that the colorless, odorless and least directly life-threatening emissions component, carbon dioxide, would become a significant global concern.
Making Connections, Drawing Conclusions
Fossil fuel emissions of CO2 from coal, petroleum and natural gas grew steadily from the 1850s onward, but it wasn't until the 1950s that scientists began to speculate that the widespread combustion of fossil fuels could lead to increased concentrations of atmospheric carbon dioxide. Their reasoning was as follows: Fossil fuel combustion consumes hydrocarbons from fuel and oxygen from the air, releasing water vapor and carbon dioxide along with the desired energy. Over time, CO2 accumulates in the atmosphere as more fossil fuel is burned and carbon dioxide is released at a greater rate than it is removed by vegetation, soil or water (see graph above).
Confirmation that atmospheric CO2 concentrations were in fact rising came later from Dr. Charles Keeling, who developed the first accurate method of measuring atmospheric CO2. He began monitoring concentrations on a dormant island volcano in Mauna Loa, Hawaii in 1959. The site proved ideal for measurements due to its lack of vegetation and human activity (which could interfere with sampling) and has produced the longest continuous record of atmospheric CO2 measurements.
According to the Mauna Loa record, also famously known as the Keeling Curve, concentrations rose from 315.98 parts per million (ppm) in 1959 to 394.16 ppm as of May 2011. The red lines in the graph below represent the actual measured concentrations and the black line is the trend line. The actual concentrations zigzag each year with the seasons, since plants consume CO2 through their growth in the spring and summer and release CO2 with their decay in the fall and winter.
The Culprits: Fossil Fuels
Scientists verified that the rise in atmospheric CO2 is due to fossil fuel combustion by examining the characteristics of the carbon atoms. Carbon originating from natural sources of CO2, such as volcanoes, oceans or geothermal, is different than carbon from fossil fuels. Fossil fuel carbon comes from ancient plant matter, and plants prefer the lighter Carbon isotope (12C) over the heavier one (13C). This means that carbon isotopes from fossil fuel combustion have a greater proportion of light carbon isotopes than the natural carbon sources. Since the proportion of CO2 made up of lighter carbon isotopes has increased in the atmosphere along with the increase in CO2, this points to fossil fuels as the main culprit in the rise of atmospheric CO2.
The level of CO2 in our atmosphere is important because of its role as a greenhouse gas. Greenhouse gases trap some of the heat reradiated from the Earth's surface that was heated by the sun. Our planet would be frigid and uninhabitable without some greenhouse gases, but high concentrations raise the global average temperature beyond the natural level that allows for the stability of the Earth's climate. Climate change has already begun to cause some glacial melting, more extreme weather patterns, including more droughts, flooding and heat waves, crop failures and wildfires. The extent of future climatic instability depends on the degree of warming that will occur, which will be determined by the profile of our greenhouse gas emissions over time.
Some scientists and policymakers are in the process of finding a stabilization target for greenhouse gases that if not exceeded would likely avoid the worst and most long-lasting damage. So far the focus is mainly on CO2, since it is emitted in greater amounts than the other greenhouse gases and remains in the atmosphere long after emission. However, there is debate about where the stabilization target should be set because of uncertainties in the exact degree of warming that increased greenhouse gas concentrations cause and uncertainties in the precise amount of warming that would lead to catastrophic effects.
The first stabilization target of 550 ppm was suggested in the mid 1990s. This number is double the concentration of pre-industrial times and commonly was used for computer modeling of future climate scenarios at the time. The Stern Review adopted 550 ppm as the upper bound for acceptable CO2 emissions based mainly on economic cost-benefit analysis of climate change mitigation.
More recently, studies by many scientific agencies and the European Union have concluded that 550 ppm is not a sufficient stabilization target, and that passing the threshold of 450 ppm is quite likely to result in severe climatic shifts. An atmospheric CO2 concentration of 450 ppm translates to a temperature increase of about 3.6 degrees Fahrenheit. According to a report by the Division of Earth & Life Studies, each degree Celsius (or 1.8 degrees F) of warming leads to:
- 5-10% changes in precipitation in a number of regions
- 3-10% increases in heavy rainfall
- 5-15% yield reductions of a number of crops
- 5-10% changes in stream-flow in many river basins worldwide
- About 15% and 25% decreases in the extent of annually averaged and September Arctic sea ice, respectively
However, after observing changes in our environment occurring more rapidly than expected from our current warming of only one degree Fahrenheit, several renowned climatologists (notably Dr. James Hansen of the NASA Goddard Institute for Space Studies and Rajendra Pachauri, leader of the Intergovernmental Panel on Climate Change) have adjusted their stabilization target to 350 ppm. They believe that we have already passed a climatic threshold and that each year that the CO2 concentration remains above 350 ppm we increase the risk of crossing tipping points for the melting of sea ice and ice sheets, shifts in climate zones detrimental to agricultural areas, the drying of Alpine water supplies, and ocean acidification.
The next article in this series will discuss ocean acidification and its impact on marine life.
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