Energy, Water, and Population Connections

 Let us look more closely at the dates when the human population reached each milestone of an added billion people on the planet. While it took us over 100 years to reach the second billion, it took only 32 years to reach the third billion, and we are now increasing our global population by about one billion every 12–13 years. This means that the human population increases by a factor of 6–7 billion in an average lifespan of 80 years. This rapidly increasing population requires a corresponding increase in food and potable water to be able to survive. Considering that the resources on the planet are finite, this rate of population increase cannot be sustained indefinitely.

The very rapid rate of human population increase in recent years has primarily been due to our ability to access stored fossil energy sources. Most of our advances that increase lifespan and decrease the death rate – including industrial and agricultural improvements, medical advances, and transportation and trade developments – are linked to the increase in the availability of low-cost fossil energy sources. In addition, fossil fuels are not only used as our primary source of energy, but also serve as raw materials for the chemical production of plastics and other commonly used polymers, as well as for the manufacture of synthetic drugs and pharmaceuticals. The trend in fossil fuel use from 1800 to 2007 is shown in Figure 1.4 as the amount of carbon combusted per year. The total amount of fossil energy used in the form of petroleum, coal, and natural gas follows a similar trend as that of the population increase for this same time period.

Fossil fuels are not renewable, and their supply is also not infinite. The Earth’s fossil fuel resources took hundreds of millions of years to be produced. Beginning with the fixation of carbon dioxide by ancient plants, the organic carbon in the dead plants was slowly deposited as kerogen sediments, which were buried deeper and deeper by sedimentation processes and finally transformed into large amounts of fossil carbonaceous materials in the form of coals, petroleum, and natural gas now found in the geosphere. The earliest known deposits of fossil fuels were first formed during the Cambrian Period, about 500 million years ago. More recent deposits were formed in the Pliocene Period, about five million years ago. It is obvious that the process that creates fossil fuels does not occur fast enough to replenish the rapidly decreasing supplies.

The use of fossil fuels as an energy source in the late nineteenth century and continuing into the twentieth and twenty-first centuries has allowed for the rapid development of our species, but it is also accompanied by a huge change in the biosphere and the surface of the geosphere, as we converted forests and grasslands to farming operations worldwide to feed the rapidly grow-ing population. Ecosystems are also destroyed during the mining of coal, and during drilling for oil and natural gas. Oil spills alone have devastated ecosystems, especially in coastal areas. Add to this the damage incurred by the emission of pollutants during the combustion of the fuels, which contributes to photochemical smog and climate change, and the result is that the planet has dramatically changed due to the widespread use of fossil energy since the late nineteenth century.

While, there are renewable energy sources that have also increased during this period – including nuclear, solar, wind, biofuels, geothermal, and hydroelectric –fossil fuels are currently the dominant source of energy in the world. The total world energy demand is about 8.8 × 1017 Wh yr−1, with oil, coal, and natural gas supplying about 92% of that demand. Renewable energy sources supply 6% of this demand, and nuclear energy supplies only 2%. The rapid use of the limited fossil fuel supplies has led to projections that within the next few decades, an energy crisis is likely to occur. While we have begun to search for and increase the use of renewable energy sources, these sources still have a long way to go to reach the huge energy demand of our world’s populations. In order to avoid this projected energy crisis, renewable energy sources must become an increasingly larger fraction of our energy demand. Not only must they keep up with the increasing population growth, but they must begin to replace fossil fuel if we are to meet future energy needs.

The increased use of carbonaceous fossil fuels has led to associated increases in ozone-producing gases formed during combustion, as well as increases in the atmospheric levels of carbon dioxide, one of the major greenhouse gases. The associated increases in agricultural crop production, particularly rice, as well as increases in animal husbandry, have also led to higher levels of other greenhouse gases, such as methane and nitrous oxide. Not surprisingly, the atmospheric levels of the greenhouse gases have also followed a similar increasing trend with increasing human population and increasing fossil energy use.

While methane and nitrous oxide have major roles as greenhouse gases in the lower part of our atmosphere, they also play an important role in stratospheric chemistry tied to ozone depletion. The important thing to note here is that many of the chemical pollutant species, like methane and nitrous oxide, have more than one impact on the environment. They can impact chemical and physical processes that can lead to air pollution, and they can also impact climate change by acting as greenhouse gases. In addition, they can be transported into the stratosphere where they can increase stratospheric ozone depletion. Thus, in order to fully understand the environmental chemistry of any molecule or material introduced into the environment, they must be examined with regard to the potential for multiple environmental impacts.

The use of higher amounts of fertilizers and pesticides for crops and antibiotics in animal husbandry is well known to lead to water pollution problems. Also, air pollutants such as nitrogen oxides and sulfur dioxide can undergo chemical transformation, transport, and wet deposition, contributing to significant water quality degradation as well as ecosystem impacts. Enhanced use of water for agriculture and for industry has consequences in terms of water quality and supply. While the Earth is the water planet, most of that water is salt water and not usable for growing terrestrial plants and crops. Agricultural demand for fresh water has led to overuse of surface waters and depletion of groundwater supplies in most populated areas. These agricultural practices have caused available freshwater supplies to be further limited due to the addition of pollutants, causing them to become no longer useful as a freshwater resource with-out water processing.

A further complication of the increasing human population is that it is not evenly distributed over the globe. We have developed concentrated areas of population in urban centers worldwide, which have their own set of environmental problems, particularly in the areas of increased water and air pollution. In 1800, only 3% of the population lived in cities. As of 2014, the number of humans living in urban centers has risen to 53% (United Nations, 2014). These large urban centers are known as megacities, large metropolitan areas with a population of 10 million or greater (Lewis, 2007). They can consist of a single city or two or more metropolitan areas that function as a single city. The first city to reach a population of 10 million was New York City in the United States in 1950. As of 2015, there are 35 megacities worldwide. Tokyo, Japan is number one, while New York City has dropped to eighth. It is clear that the majority of the human population lives in the northern hemisphere, and Asia, Africa, and South America are areas where these urban centers are rapidly growing.

This change in population density is projected to continue, with urban populations increasing and rural populations declining. In addition, the population of these urban megacities has also been increasing along with the increase in overall global population. All of the large urban centers suffer from similar issues of high air pollution levels, water shortages, high energy demand, and waste-handling problems. Consequently, the megacities are areas where environmental pollution and energy, food, and water shortages are most likely to occur in the future. The megacities also act as very large pollution sources, which can impact regional and global air and water quality. These increasing problems in the megacities worldwide demonstrate the need to develop clean and safe mass-transit systems, efficient sanitation systems, and the wide use of renewable-energy sources that can sustain the needs of industry as well as urban households and recreation facilities. Balancing the increasing energy, food, and water demands against chemical pollution in the megacity centers is one of the major problems we face in the coming decades.

While we have recognized that the population–energy–food web has primarily evolved in areas where increasing population requires more energy, water, and food leading to more pollution and a degradation of air and water quality, we have not yet been successful in putting better practices and technologies in place to insure a sustainable system in the future. With a rapidly increasing population and rapidly depleting limited resources, we may soon be faced with a dire situation globally with no good solutions available. There is clearly a need for future scientists to be trained to think proactively in order to address these problems before they become critical, and to be able to communicate their ideas and findings in a timely fashion so that national and international policies can be put in place to develop a sustainable situation for humankind and the planet. As noted earlier, the chemical and physical properties of pollutant species and their potential impacts on environmental systems need to be addressed based on our best understanding of all of the Earth’s systems. These impact assessments need to be strongly based on the fundamental principles of environmental chemistry and physics. While we may not be able to find the perfect solution for these very large and complex problems linked to increasing human populations, we do need to determine the best solutions that will minimize the ever-growing impacts.