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coal, the energy content and the carbon content vary. For example, bituminous coal is the most plentiful type in the United States. Its carbon content ranges from 45% to 86%, and its energy content varies by approximately ±20% around the average. The calculated value for coal given above using graphite as a model produces a result corresponding to the middle of the range of energy content of bituminous coal. Natural gas can have as much as 20% of the gaseous hydrocarbons ethane (C2H6), propane (C3H8), and butane (C4H10), in addition to methane (CH4). The mixture hardly changes the energy content or the energy per CO2 produced compared to that calculated for pure methane. The same is true of oil, which is a mixture of long chain liquid hydrocarbons.

Real Numbers for Carbon Dioxide Production from Generating Electricity

The energy content of fossil fuels does not take into account power plant efficiencies, that is, the conversion of the fuel’s energy into electricity. The efficiencies of power plants, which vary depending on design and age, are similar regardless of the type of fossil fuel used. Typically, the efficiency is in the high 30s to 40% range. This means that only approximately 40% of the fuel’s energy is converted to electrical energy. In addition, the loss in power transmission lines is approximately 7%. Thus, if a plant efficiency value of 38% is combined with the transmission line loss the overall rate of conversion of fossil fuel energy to usable electricity in our homes is approximately 35%.

To understand what this means, let’s calculate how much CO2 is produced by a 100-watt lightbulb that burns 24 hours a day for a year. A watt is a J/s (one joule for one second). A year is 3.2 × 107 seconds. So, our 100-watt lightbulb will consume 3.2 × 109 J in a year. For natural gas, we said that one molecule of CO2 is produced for each 1.4 × 10-18 J of chemical energy produced. To get 3.2 × 109 J of energy, we will produce 3.2 × 109/1.4 × 10-18 = 2.3 × 1027 molecules of CO2. This amount is for perfect efficiency. With 35% overall efficiency, 6.4 × 1027 molecules of CO2 will be produced. 6.02 × 1023 molecules of CO2 weighs 44 g (grams). So, the weight in grams of the CO2 produced is 5 × 105 g or 1000 pounds. What we see is that running a 100-watt lightbulb for a year will put 1000 lb of CO2 into the atmosphere using natural gas. If we burn coal, it will be 2000 lb, or one ton. That is the weight of a small car. The first message is turn off the lights when you aren’t using them. That computer you leave on 24/7 uses 200 to 300 watts of electricity. So, if you get your electricity from a coal-fired power plant, your computer is responsible for putting 2 to 3 tons of CO2 into the atmosphere every year. The second message is that efficiency of the electrical devices we use and the choice of fossil fuel really matters. A compact fluorescent bulb that produces the same amount of light as a 100 W conventional bulb uses only 25 W. So a compact fluorescent running for a year from a natural gas power plant produces 250 lb of CO2, which should be compared to a conventional bulb run from a coal power plant that produces 2000 lb of CO2.

CARBON DIOXIDE IS A GREENHOUSE GAS BECAUSE OF QUANTUM MECHANICS

Why is carbon dioxide such a serious problem as a greenhouse gas? In other words, why does it trap heat in the atmosphere? And, why is water vapor (gas phase water molecules in the atmosphere) actually worse than CO2 as a greenhouse gas? The amount of water vapor is determined by evaporation and condensation of water. The Earth has huge pools of water, the oceans, from which water evaporates into the atmosphere. We also have rain, dew, and snow that remove water from the air. Humans have little effect on the amount of water in the air, although if the Earth continues to warm, the atmosphere will have more water vapor. The additional water vapor will amplify the influence of adding CO2, making greenhouse warming worse. H2O is a powerful greenhouse gas. However, we can influence the amount of CO2 in the air by the energy