Like all other consumers in the food pyramid, humans use energy from the plants and animals that they eat to maintain their bodies’ health and basic metabolic energy requirements. Unlike other organisms, humans also use energy to support the complex needs of their culture and lifestyles. Transportation, farming, manufacturing, heating and cooling homes and buildings, entertaining, and many other human activities all need energy.
The Industrial Revolution will be discussed again in the upcoming Energy and Ethics section. It is important to know this historical context in order to understand why the world faces so many challenges in environmental ethics today.
Prior to the beginning of the Industrial Revolution in the 1700’s, essentially all the non-food energy used by humans for heating and cooking came from harvesting biomass (primarily wood, peat, and animal dung). However, the rise of the Industrial Revolution throughout Europe created an increased demand for biomass. As a result, trees began to be cut down more rapidly than they could be grown, leading to an energy crisis in the 18th century. In response, Europeans began using coal as a primary energy source.
The process of industrialization was propelled by many technological inventions, among which perhaps the most important was the invention of the steam engine. A steam engine is essentially a heat engine – a system that converts heat into mechanical energy (Figure 8). Coal is burned to heat water; heated water produces steam which has an expanded volume and puts
pressure on a piston that turns a wheel. If we take the steam engine one step further and replace the wheel with a coil of wire housed in a large magnet, we get the basic construction of most electrical generators (i.e. coal-fired power plants). The generated electrical energy is then used to power our lights, refrigerators, computers, air conditioners, and heaters.
It is important to recognize that these non-food energy consumptive activities of humans are also governed by the First and Second Laws of Thermodynamics (Figure 9). In the example of powering an incandescent light bulb, the total amount of energy in the system remains 100 units, due to the First Law of Thermodynamics. However, a significant portion of useful energy is lost in every step of the process due to the Second Law of Thermodynamics. Therefore, of the 100 units of chemical energy that comes from the coal, only 1.2 units are converted into light, which is the form of energy that is useful to humans. The remaining 98.8 units are lost as heat during the process of conversion. This is similar to the low efficiency of energy transfer in the food pyramid which was highlighted earlier in this section.
If we look at how the sources of energy used to fuel human activities have changed in the past 165 years (Figure 10), we notice that in 1850 almost all of the world’s energy supply came from biomass. Biomass is still predominantly used in many parts of the world today, especially in rural areas of developing countries. However, the use of fossil fuels, in particular oil (shaded in orange) quickly dominated global energy usage in the years following World War II.
In 2008, approximately 80% of the world’s energy was derived from fossil fuels, predominantly coal, oil and gas. In the last few decades, other energy sources, such as nuclear and hydro-power, have been added, however, these still represent only a small fraction of the world’s total energy consumption. The thin green strip at the top of the graph represents the amount of energy generated from clean renewable sources such as wind, solar, and energy drawn from ocean tides.
In the upcoming Energy and Ethics section you will consider the moral goal of transitioning to renewable energy.
Our relative recent (the last 75 years) and heavy reliance on fossil fuels has led to the greatest human challenge of the 21st century – global climate change. In order to stop and reverse the impacts of fossil fuel emissions on climate, we must greatly expand the development and use of technologies that allow us to harvest cleaner, more sustainable energy sources like solar, wind, and geothermal.
Questions to Consider
Move ahead to Chapter 6 and look at Figure 4 showing atmospheric concentrations of three greenhouse gases over time. Come back to this chapter and look again at Figure 10 above which shows the increase in world energy use.
- What relationship do you see between the information given on these two figures?
- What do you think it would take to change the trend lines on these two figures?