The environmental effects of using fossil fuels can have a serious impact on the quality of life. The process of burning fossil fuels combines carbon in the fuel with oxygen in the air to form carbon dioxide (CO2) that is released to the atmosphere. This is true for all fossil fuels and more so with coal and oil. The United States produces over 6 billion tons of CO2 each year that is released into the atmosphere; 35% of this is from coal-fired power stations.
Today, carbon dioxide levels are at historic high levels, the evidence of which can be traced back 420,000 years from analysis of ice cores taken at Vostok, Antarctica. Carbon dioxide is a natural constituent of the atmosphere, but it is also a greenhouse gas that contributes to global warming. It is not a simple matter to sequester carbon dioxide and prevent it from getting in the atmosphere, so levels will continue to build for the foreseeable future until economic and reliable carbon capture can be implemented.
Carbon dioxide capture is an ongoing research area, and commercial scale CO2 capture has been tested in a 25 megawatt (MW) coal-fired plant in Alabama, with over 100,000 tons of CO2 captured to date.
Carbon dioxide gets the most attention for burning fuels, but other pollutants are also released. When gasoline is burned in a motor vehicle, it produces carbon monoxide, a poisonous gas, and releases nitrous oxides, ozone, and benzene.
Coal is not pure carbon or hydrocarbons; it also contains small amounts of sulfur and other toxic materials that are released when it is used as a fuel. Sulfur dioxide is another atmospheric pollutant that contributes to forming acid rain and the acidification of oceans and lakes.
Coal burning also results in fly ash in the form of a fine residue, which gets in the atmosphere, and bottom ash, which is the residue in the burners. Coal ash also contains traces of poisonous heavy metals such as arsenic, lead, and mercury; these pollutants are hazardous to human health, as well as fish and other wildlife.
Atmospheric CO2 gets most of the attention, but another aspect to increases in CO2 is acidification of the oceans. When atmospheric CO2 is absorbed by water, it creates acid. There is clear evidence of an increase in the acidity of the world’s oceans, which will ultimately have very serious consequences to marine life, particularly shellfish, coral reefs, and certain types of plankton at the bottom of the food chain.
The shells of shellfish can dissolve in a more acidic environment, and corals stop building reefs. The loss of corals will have profound effects on the marine food chain, ultimately affecting fisheries.
In addition to pollution caused by burning fossil fuels, the process of obtaining these fuels has led to some major environmental disasters, such as the infamous Exxon Valdez spill and the British Petroleum (BP) Gulf of Mexico oil spill. Coal has been particularly hazardous to obtain.
Even natural gas, which is the cleanest burning of the fossil fuels, contributes to environmental damage and health problems. Not all methane in natural gas burns, so some methane is released to the atmosphere. The overall impact of greenhouse gases is determined by several factors, including the residence time in the atmosphere—a longer residence time has a greater impact. Ton for ton, methane has a greater impact as a greenhouse gas than carbon dioxide; however, it has a shorter residence time and there is much less methane released than carbon dioxide.
Carbon dioxide has an average residence time of over a century before it is removed, whereas methane’s residence time is only ten years. The net impact on global climate change is higher for carbon dioxide than for methane. The burning of fossil fuels adds carbon dioxide and methane (as well as other pollutants) to the atmosphere.
In appliances such as stoves, natural gas contributes to significant indoor pollution because stoves are generally not vented to the outside, thus trapping the gas inside. This can create a health hazard, particularly for people with respiratory problems.
Obtaining natural gas via a technique called hydraulic fracking is controversial. Fracking has its origins in a natural process where fluid seeps into rocks, and the resulting pressure breaks the rocks and enables natural gas and oil to find an easier path to seep out.
Human fracking consists of drilling a well over a mile below the earth’s surface to reach shale deposits. The drilling rig then turns the drill horizontally and drills another 4,000 feet through the shale deposit. The final step in this process is to pump millions of gallons of water, sand, and chemicals into the well to shatter the shale, which allows trapped natural gas, oil, propane, and butane to the surface where it is captured and sent through existing transportation pipelines. Sometimes material injected into the shale is a mixture that includes sand, ceramics, or sintered bauxite as a fracturing fluid, or it may be in the form of a foam, gel, or gas.
The procedure is considered to be controversial because it is not possible to know all of the environmental effects associated with fracking, but there is evidence of natural gas contamination of groundwater in Pennsylvania and there may be other potential environmental impacts, such as effects on the water table. There is also evidence that fracking has been responsible for two rather small earthquakes in England in the spring of 2011.
Water usage and disposing of warm water with all fossil-fueled power plants, and with thermal cycle power plants in general, are also issues. In any heat engine, the temperature difference between the heat input and the heat rejected is related to the work done. A greater efficiency is obtained when the temperature difference is higher.
Water is the most widely used coolant for power plants because it has very high heat capacity and can remove heat efficiently. Water is an excellent coolant, but steam-operated power plants require massive amounts of cooling water. One method of cooling, called once-through cooling, takes water from a source (usually a river) and puts warmed water back into the source. The warmed water can have a deadly effect on aquatic life.
A widely used alternative to river water for cooling is evaporative cooling, which uses huge quantities of water. Waste heat is removed by evaporating the water in large cooling towers rather than returning it to its source. Water is a precious resource, so it is an issue that must be considered for power plants.
In drought conditions, such as those that occurred in the summer of 2012, the lack of water at some power stations required several power plants to cut back production. In hot dry summers, this problem becomes especially acute, with power plants, farmers, ranchers, and fisheries all competing for this valuable resource.