GEOG 438W
Human Dimensions of Global Warming

Greenhouse Gas Emissions from the Energy Sector

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Figure 4.6 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.

Pie chart of global CO2 emissions by country from fossil fuel combustion (2015)
Figure 4.6: Share of global carbon dioxide emissions from fuel combustion (2015).
Click here for a text version of figure 4.6
The image is a pie chart represented below as a table.
World carbon dioxide emissions from the consumption and flaring of fossil fuels, 2006.(Million Metric Tons of Carbon Dioxide)
Country Percentage
China 28%
USA 15%
India 6%
Russia 5%
Japan 4%
Germany 2%
South Korea 2%
Iran 2%
Canada 2%
Saudi Arabia 2%
Rest of the World 31%

Figure 4.7 is a graph depicting fossil fuel-based CO2 emissions for China and the U.S. from 1990 to 2006. A dramatic uptick in China’s emissions took place after the turn of the century, while the U.S. emissions started to flatten out and drop at the end of the period. These trends have continued in the last five years. It is important to note that estimates attribute one third of China’s emissions to their exports, and 20 percent of those exports go to the U.S. Thus, this fact implies that U.S. CO2 emissions should be higher and China’s emissions lower. In any case, both nations emit the lion’s share of world’s CO2.

Graph showing CO2 emissions from the consumption and flaring of fossil fuels, U.S. and China. Important trends described in text above
Figure 4.7: Carbon dioxide emissions from the consumption and flaring of fossil fuels, 1990 - 2006. 

Figure 4.8 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.

Chart showing GHG emissions from electricity-generation systems.  See text version link in the caption for details
Figure 4.8: GHG emissions from electricity-generation systems.
Click Here for a text description of Figure 4.8
The image is a bar chart represented as a table below. Numbers are approximate.
GHG emissions from electricity-generation systems
Note: numbers are approximate
Electricity Generation System Stack Emissions
(tonnes CO2-eq/GWhel)

Other stages
((tonnes CO2-eq/GWhel)

Lignite (FGD, high) 1300 1300-1350
Lignite (FGD, low) 1025 1025-1050
Coal (FGD, high) 1020 1020-1025
Coal (FGD, low) 750 750-825
Coal (with CCS) 150 150-175
Heavy fuel oil (low-NOx) 700 700-775
Heavy fuel oil (combined cycle) 600 600-650
Natural Gas, combined cycle (high) 375 375-500
Natural Gas, combined cycle (low) 350 350-400
Natural Gas, combined cycle (SCR) 375 375-500
Natural Gas, combined cycle (with CCS) 175 175-250
Photovoltaic (high) - 125
Photovoltaic (low) - 25
Hydro (high) - 100
Hydro (low) - 5
Tree plantation (IGCC, high) - 50
Tree plantation (IGCC, low) - 20
Wind (offshore, high) - 25
Wind (offshore, low) - 5
Wind (onshore, high) - 20
Wind (onshore, low) - 5
Nuclear (high) - 50
Nuclear (low) - 0

The final graphic in this section (Figure 4.9) 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 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.

Bar chart comparing CO2 emissions and efficiency
Figure 4.9: Carbon dioxide emissions and conversion efficiencies of coal and gas-fired power generation, and combined heat and power plants.
Click here for a text description of Figure 4.9
The image is a bar chart represented as a table below. Numbers are approximate.
Carbon dioxide emissions and conversion efficiencies of coal and gas-fired power generation, and combined heat and power plants
Note: numbers are approximate
Energy Generation System CO2 Emissions (kg CO2/MWh Efficiency (Percentage)
Traditional coal fired steam turbine 995 30
New clean coal fired steam turbine 775 40
Coal gasification gas turbine 700 45
New combined-cycle gas turbine (CCGT) 375 55
CGP coal-fired 500 80
CHP gas-fired 275 80

Credit: 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, Cambridge, United Kingdom and New York, NY, USA. Chapter 4.3.6. Retrieved July 11, 2011 from http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch4s4-3-6.html.