To understand emissions sources, it's useful to categorize those emissions. One such way to do that is by sector. This lesson is going to look specifically at Energy, which is the biggest source of anthropogenic GHG emissions (by far!). More specifically, we are going to break down energy into a few subcategories: power generation, transportation, and industrial processes, as shown below. This lesson, we'll be focusing on the subset of that big almost-the-whole-piece-of-the-pie energy sector.
Energy use and consumption produce more GHG emissions than any other realm of human endeavor. A brief look at the socioeconomic drivers of energy use and consumption helps explain some of the reasons why. Current technologies for generating energy focus on GHG-intensive fossil fuels; the economic system favors producing the greatest amount of energy at the lowest cost and does not account for the environmental costs of energy production; political and legal institutions promote and protect fossil-fuel industries and typically fail to foster alternative energy sources adequately, and Western lifestyles are energy-intensive but many non-Westerners aspire to a Western lifestyle. Add to that the exponential growth of Earth’s human population and it is no wonder that GHG emissions continue to grow rapidly.
Global GHG emissions from energy use and production far outweigh emissions from other activities. The industrial processes, agriculture, land-use change and forestry, and waste management sectors together account for 37 percent of all global GHG emissions in the accompanying pie chart. However, a significant proportion of the emissions from agriculture and from land-use change and forestry involve fossil fuel consumption, so the percentage of emissions from energy is greater than the graphic implies. Consequently, far more than two thirds of all GHG emissions result from energy use and production.
In the pie chart, electricity and heat production is clearly the largest emitter of GHGs, being responsible for over one quarter of total emissions. Most of these emissions are attributable to society’s dependence on coal and secondarily on natural gas. The remaining energy categories –– manufacturing and construction, transportation, and “other” –– each contribute approximately equal proportions of the global GHG emissions.
Going beyond this particular graphic, when compiling the national GHG emissions inventory, the US breaks its energy sector emissions into three broad categories: mobile sources, stationary sources, and fugitive sources.
The stationary sources category is large and includes many activities.
There are many other important categories of GHG-producing activities:
Even so, these enterprises consume huge amounts of electricity, and most of this electricity comes from fossil fuel-powered power plants, so these categories are indirectly responsible for a very large proportion of GHG emissions.
In addition to transportation and stationary sources, fugitive CH4 emissions from coalmines and from oil and natural gas drilling sites, as well as from natural gas pipelines, were thought to be a relatively small source of GHG emissions. Recent work, however, suggests that fugitive emissions may in fact be a major source of atmospheric CH4, so this part of the energy sector is coming under increased, intense scrutiny.
The relationships among energy production, energy storage and distribution, energy marketing, and energy demand and consumption are extremely complex. Thus, trying to pin GHG emissions to any one component in this complex web is arbitrary. Indeed, calculating emissions from the energy sector is fraught with error because of this complexity. It is best to think not in terms of exact proportions of GHG emissions from any one activity or subsector, but in terms of which categories are the big players.
The world consumes massive quantities of energy, with much of that energy embodied by GHG-emitting fossil fuels.[1] This image shows primary energy consumption by world region in 2015. Together, China and the United States represent 40% of global energy consumption. This is why our cooperation to solve climate change-related challenges is so pivotal.
The next image shows a graph of global consumption by fuel type for 1990-2016. Overall consumption has almost doubled in this time period (and has more than doubled if we went back 40 years). The three fossil fuels (oil, coal, and natural gas) dominate, encompassing between 80 to 90 percent of energy consumption throughout the period. Oil provides the largest proportion of energy, but proportionally has lost ground to coal and especially natural gas (why might that be?). Coal has had an upsurge in the 21st century, especially after 2005, and may become the leading fossil fuel in the future as oil supplies drop and demand for energy increases in places such as China and India, with massive coal reserves but little oil and natural gas. Biomass and hydroelectric power grew a little. Other renewables are a trivial proportion of the global energy picture. Clearly, the grip of the GHG-producing fossil fuels on the world energy picture is strong.
The next image shows a map of per capita energy consumption across the globe. An obvious general pattern emerges: low-latitude countries have very low per capita consumption –– and therefore low per capita GHG emissions –– while mid- to high-latitude countries have high per capita consumption and emissions. (Exceptions exist. For example, Saudi Arabia has anomalously high per capita energy consumption compared to surrounding countries because it is a wealthy, oil-rich country with a low population.) On the one hand, the pattern suggests that low-latitude countries with very low per capita energy consumption and very high populations such as China, India, and Indonesia, will become significant sources of GHGs as their per capita consumption figures rise. Indeed, China, which has the world’s largest population, has rapidly rising per capita energy consumption. Combined with its focus on coal as its primary energy source, China is now the world’s largest emitter of GHGs. India is hot on China’s heels, with a rapidly expanding coal-based economy. On the other hand, the pattern also suggests global inequities because the mid- to high-latitude countries have such very high per capita energy consumption figures. Opportunities exist for these countries to reduce per capita consumption by undertaking energy efficiency measures, adopting non-GHG-producing energy types, and modifying their energy-intensive lifestyles. This contrast between the low latitudes (the global South) and the mid- to high latitudes (the global North) is at the heart of the ongoing United Nations climate negotiations.
[1] Most of the remainder of this lesson is based on figures presented in Sims, et al., 2007. Energy supply. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, et al. (eds)], Cambridge University Press.
The next image shows CO2 emissions from fossil fuel combustion by country. In 2015, China's share was 28 percent of the world’s CO2, while the US share was 15 percent. The next closest country, India, emitted about 6 percent of the CO2. Clearly, to bring down global emissions from the energy sector, China and the US must lead the way.
The next image is a graph depicting fossil fuel-based CO2 emissions for the US, China, several other key emitters, and the aggregate rest of the world between 1970-2017. What jumps out at you?
The next image displays the GHG emissions from the various systems used to generate electricity. Clearly, coal and its close cousin lignite produce the most GHG per unit of energy produced. Fuel oil is the next most GHG-intensive generation system. Natural gas, which is often touted as the clean alternative to coal, certainly emits about half as many GHGs per unit of energy but is still extremely GHG-intensive compared to non-fossil fuel alternatives. Renewables and nuclear produce trivial quantities of GHGs compared to the three fossil fuel types –– coal, oil, and natural gas.
The final graphic in this section illustrates the fact that CO2 emissions go down as efficiency in burning fossil fuel in power generation goes up. For coal, new technologies improve efficiencies and reduce emissions –– but they are still exceptionally high compared to the alternatives. New natural gas power generation is about half as CO2-intensive as the best single-purpose coal-fired power plant. Cogeneration (also known as CHP, combined heat and power) is dual-purpose and drastically improves the efficiency of any fossil fuel power generating system, halving the efficiency of single-purpose systems.
Links
[1] http://cait.wri.org/
[2] https://creativecommons.org/licenses/by/4.0/
[3] http://www.wri.org/our-work/project/earthtrends-environmental-informationupdates/node/296
[4] https://www.carbonbrief.org/explained-fugitive-methane-emissions-from-natural-gas-production
[5] https://www.wri.org/blog/2013/04/close-look-fugitive-methane-emissions-natural-gas
[6] https://www.eia.gov/outlooks/ieo/pdf/0484(2017).pdf
[7] https://www.iea.org/reports/key-world-energy-statistics-2021/supply
[8] https://www.ipcc.ch/report/ar4/wg3/energy-supply/
[9] https://www.ucsusa.org/global-warming/science-and-impacts/science/each-countrys-share-of-co2.html#.W575uqinGUk