Skip to main content

Hotter summers, stronger hurricanes, extreme flooding events, melting ice in the polar regions – are these events related to changes in climate due to the increase in greenhouse gas emissions from human activity? The evidence gathered by scientists around the world seems to point to this conclusion, one that is becoming more convincing over time. Scientists agree that human activity, such as burning fossil fuels, has led to an increase in the concentration of carbon dioxide (CO2) and other gases that are causing changes to Earth’s climate.

Climate change, or more specifically global warming, refers to the warming of Earth’s atmosphere due to the greenhouse effect. Incoming solar energy, including certain wavelengths of infrared radiation, passes through Earth’s atmosphere and reaches the surface of Earth, thus warming it. Some of the infrared radiation emitted from the Earth’s surface returns back to the atmosphere, where it is absorbed by certain atmospheric gases called greenhouse gases. This absorption warms the atmosphere of Earth, similar to how a greenhouse captures solar energy and warms the air inside it.

Natural levels of greenhouse gases keep Earth at an average temperature of 59°F (15°C). Without their presence, the average temperature of Earth would be about 0.4°F (18°C)1. However, increases in greenhouse gas emissions due to burning fossil fuels, certain manufacturing processes, changes in agricultural practices, and deforestation have led to increased levels of these gases in the atmosphere. This, in turn, strongly suggests a cause for the observed increase in average global air temperature of 0.5°F to 1.1°F (0.3°C to 0.6°C) over the past century2.

The major greenhouse gases include carbon dioxide (CO2), water vapor (H2O), and methane (CH4), as well as nitrous oxide (N2O) and ozone3. Carbon dioxide is the greenhouse gas that is of greatest concern due to its large atmospheric concentration with respect to other greenhouse gases and the large amounts emitted. Worldwide concentrations of COhave increased from 280 parts per million (ppm) by volume before 1750, the pre-industrial period, to 397 ppm in 2014, a 42% increase. More recently, atmospheric CO2 concentrations have climbed to 414.5 ppm in March of 20204.

Click the following website to see a graph showing Atmospheric CO2 at Mauna Loa Observatory from 1958 to present: 

China is the largest emitter of carbon dioxide, emitting 9.84 billion tons in 2017. After China, the nations with the largest emissions for 2017 were the United States (5.27 billion tons), followed by India (2.47 billion tons)5

For more information concerning carbon emissions, reference Our World in Data by the University of Oxford: 

Although CO2 is the most prominent greenhouse gas, other greenhouse gases are either more common in Earth’s atmosphere (such as water vapor) or are more effective in absorbing infrared radiation from Earth’s surface (such as methane, nitrous oxide, and chlorofluorocarbons). On the other hand, nearly all other greenhouse gases are present in the atmosphere in much lower concentrations than CO2. For example, methane is 28 times more effective in absorbing infrared radiation compared to CO2 but is present at concentrations that are 0.45% of those of CO2 (see table below).

Global Warming Potential of Selected Greenhouse Gases

Greenhouse Gas

Global Warming Potential Relative to CO21

​Atmospheric Concentrationa

Carbon Dioxide (CO2) 1 412.5 ppm (as of April 20, 2020)2
Methane (CH4)​ 28  1,874.7 ppb (as of December 2019)3
Nitrous Oxide (N2O) 265 332.4 ppb (as of December 2019)4
CFC (Freon)-12 (CCl2F2)​ 10,200 500 ppt (as of January 2020)5

1Blasing, T.J. Recent Greenhouse Gas Concentrations. Oak Ridge, Tenn. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratories, Oak Ridge, Tenn. Accessed September 28, 2022.

2National Oceanic & Atmospheric Administration (NOAA). “Recent Daily Average Mauna Loa CO2.” NOAA Global Monitoring Laboratory, Accessed April 21, 2020.

3National Oceanic & Atmospheric Administration (NOAA). “Global CH4 Monthly Means.” NOAA Global Monitoring Laboratory, Accessed April 21, 2020.

4National Oceanic & Atmospheric Administration (NOAA). “Global N2O Monthly Means.” NOAA Global Monitoring Laboratory, Accessed April 21, 2020.

5National Oceanic & Atmospheric Administration (NOAA). “Chlorofluorocarbon-12 (CCl2F2)- Combined Data Set.” NOAA Global Monitoring Laboratory, Accessed April 21, 2020.

aparts per million (ppm), parts per billion (ppb), parts per trillion (ppt) by volume of gas

Because many different greenhouse gases are emitted due to human activities, many scientific and policy organizations report greenhouse gas emissions in terms of carbon dioxide equivalents (CO2e), which are developed by combining the global warming potentials and the concentrations of the different greenhouse gases into a single value. This summary primarily addresses CO2 emissions, although CO2 equivalent values for greenhouse gases are noted in the text as well.

Does the destruction of the ozone layer cause global warming?6

Some believe that the destruction of the ozone layer is directly responsible for global warming because reduced amounts of ozone allows increased amounts of solar radiation to reach Earth’s surface, thus heating it. However, the two processes are different. Global warming results when increased concentrations of greenhouse gases more effectively trap infrared radiation coming from the surface of Earth after the surface has been warmed by visible and infrared radiation.

The stratospheric ozone (O3) layer, located about 13 to 25 miles (20 to 40 Kilometers) above Earth’s surface is diminished when chlorofluorocarbon compounds (CFCs), a subset of fluorocarbons, are released into the atmosphere from discarded air conditioners and manufacturing processes that use these compounds. Once released, CFCs break down, freeing chlorine atoms to attack ozone molecules. Reduced ozone concentrations at these altitudes allow increased levels of ultraviolet radiation to reach Earth’s surface that would otherwise be absorbed by the ozone. While increased ultraviolet can damage plants and lead to elevated levels of skin cancer in humans, it is not the form of radiation that results in global warming.

Despite being different processes, the CFCs that cause damage to the ozone layer are also potent greenhouse gases that are in the range of 10,0007 times more effective at absorbing infrared radiation from Earth’s surface than CO2. Hence, CFC emissions affect both global warming and the ozone layer.

The major causes of increased greenhouse gas emissions into the atmosphere are fossil fuel combustion, agricultural practices, and industrial processes. Deforestation also affects the balance of atmospheric CO2 since trees absorb this gas during photosynthesis.

Fossil fuels such as coal, oil, and natural gas are burned to produce energy for transportation, heat for buildings, electricity generation, and industrial processes and account for the majority of CO2 emissions in the United States8. The amount of CO2 produced by fossil fuels varies with respect to the amount of carbon in the fuel and its energy content. Coal produces the most CO2 per unit of energy, followed by petroleum and its products, and by natural gas, which produces the lowest amount of COper unit of energy.

Biomass, such as wood, along with biofuels, such as ethanol, methanol, and biodiesel, also emit CO2 when burned. The amount of CO2 they produce per unit of energy is comparable to corresponding figures for petroleum products. However, unlike fossil fuels, biomass and biofuels are renewable energy resources that form a complete carbon cycle, provided they are grown sustainably. For example, growing a new corn crop will absorb the CO2 emitted when the ethanol produced from a previously harvested corn crop is burned in a car engine.

How much CO2 is absorbed by trees?

The amount of CO2 absorbed by trees varies widely depending on the age, type of tree, climate, and the characteristics of the surrounding ecosystem. Hence figures which state the amount of CO2 absorbed per tree or per acre of trees may also vary widely. According to one source, “a healthy, growing tree absorbs between 13 and 48 pounds of CO2 per year. At the 13 pound rate, one acre of trees absorbs 2.6 tons of CO2per year.”9 Another source states that “a forest absorbs about 3 tons of CO2 per acre of trees per year.”10 From these figures, an acceptable estimate for CO2 absorption by trees would be 13 pounds of CO2 per tree per year and 3 tons of CO2 per acre of trees per year.

The following table provides a list of CO2 emissions factors for various fuels in terms of pounds of CO2 produced per a selected unit, such as tons of coal or gallons of liquid fuel, and per Million Btu of energy produced.

Type of Fuel

Pounds of CO2 per Selected Unit

Pounds of CO2 per Million Btu of Energy

Anthracite 5,685 per Ton 227
Bituminous 4931 per Ton 205
Subbituminous 3716 per Ton 213
Lignite 2792 per Ton 215
121 per 1000 cubic feet
12.1 per hundred cubic feet (CCF)
11.7 per Therm
Diesel (No. 1 and No. 2 Fuel Oil) 22.3 per Gallon 161
Gasoline 19.6 per Gallon 156
Jet Fuel 21.1 per Gallon 153
Kerosene 21.5 per Gallon 160
LPG (Liquified Petroleum Gases) 12.8 per Gallon 139
Propane (C3H8) 12.7 per Gallon 139
Methanol (CH3OH)b 9.1 per Gallon 157
Ethanol (C2H5OH)b 12.6 per Gallon 166
Biodiesel (B100)c See Ethanol See Ethanol
Wood (average)a,d 1.70 to 1.91 per Pound
3,400 to 3,812 per Ton

aU.S. Department of Energy, Energy Information Administration. Voluntary Reporting of Greenhouse Gases Program – Fuel and Energy Source Codes and Emission Coefficients. Washington, DC., U.S. Department of Energy, Energy Information Administration. Accessed August 7, 2007. 

bBased on stoichiometric calculations under ideal combustion conditions.

cThe IPCC report on 2006 guidelines for greenhouse gas emissions inventories recommends using ethanol emissions factors for biodiesel. Gregg Marland, Carbon dioxide Information Analysis Center, Oak Ridge National Laboratories, Oak Ridge, TN; personal communication.

dU.S. Environmental Protection Agency. Technology Transfer Network Clearinghouse for Inventories and Emissions Factors.Washington, DC., U.S. Environmental Protection Agency. Accessed October 29, 2006.

Residential CO2 Emissions in Wisconsin – Energy Use and Your Utility Bill

In 2015, Wisconsin homes used 72.41 trillion Btu’s of electricity11. With approximately 62 percent of this total electricity generation coming from coal, Wisconsin’s consumption remains carbon intensive11. For an up-to-date profile of Wisconsin’s energy usage, reference the U.S. Energy Information Administration’s State Profile and Energy Estimates13. Further information on residential CO2 emissions, including a summary of approaches for reducing emissions, can be found here

Reducing residential CO2 emissions often goes hand in hand with almost all energy conservation and efficiency practices. Driving a more efficient vehicle, insulating a home, replacing incandescent light bulbs with compact fluorescent (CFL)  or light emitting diode (LED) bulbs, and purchasing energy-efficient appliances will reduce CO2 along with other air pollutant emissions.

Required Assignment for Registered Online Module Participants:

Take a look at your own home energy use on your utility bill. Check out this page for more information: Energy Use and Your Utility Bill. Then check out this online Utility Bill. Once you enter your user data, there is an option to calculate the CO2 emissions from using electricity and natural gas in the home*. You can use the Utility Bill to see how CO2 emissions are reduced by putting in values for electricity and natural gas use based on the energy conservation measures you have adopted.

*Note that the CO2 emissions factor that is embedded in the Utility Bill is 1.422 lbs/kWh for electricity which is based on an average for Wisconsin utilities for 2002. The 2018 CO2 emissions factor for Wisconsin was slightly lower at 1.394 lbs/kWh12. The COemissions factor for electricity produced by your utility may vary somewhat from this figure.

CO2 and Greenhouse Gas Emissions Calculators

While the Energy Bill calculates CO2 emissions produced when using electricity and natural gas, other CO2 and greenhouse gas emissions calculators on the web can determine the amounts of these emissions due to a wide range of residential energy uses. Some calculators calculate the user’s carbon footprint, an overall impact from greenhouse gases produced by the user due to their energy and resource use.

References Greenhouse gas. Accessed October 10, 2014. 

2Brown, Theodore L., H. Eugene LeMay, Jr., Bruce E. Bursten, and Julia R. Burdge. Chemistry: The Central Science, 9th ed.Upper Saddle River, NJ. Prentice Hall, Pearson Education, Inc. 2003. Greenhouse gas. Accessed October 10, 2014. 

4National Oceanic & Atmospheric Administration. Trends in Atmospheric Carbon Dioxide. Mauna Loa CO2 Annual Mean Data. NOAA Research. Earth System Research Laboratory. Global Monitoring Division. Global Greenhouse Gas Reference Network. Accessed May 1, 2020.

5International Energy Agency. Global CO2 Emissions in 2019. Paris, France. International Energy Agency (IEA). February 11, 2020. Accessed April 20, 2020.

6Carbon Dioxide Information Analysis Center. Frequently Asked Global Change Questions. Oak Ridge, Tenn. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory. Question #12. Accessed September 28, 2022.

7 Blasing, T.J. Recent Greenhouse Gas Concentrations. Oak Ridge, Tenn. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratories, Oak Ridge, Tenn. Updated February 2014. Accessed September 22, 2014.

8Larson, John, Damassa, Thomas, and Levinson, Ryan. Charting the Midwest: An Inventory and Analysis of Greenhouse Gas Emissions in America’s Heartland. World Resources Institute. October, 2007. p. 7-8.

9Center for Energy and Environmental Education, University of Northern Iowa, 1995.

10US Department of Energy, National Energy Technology Laboratory. Carbon Sequestration – Frequently Asked Questions. Washington, DC., U.S. Department of Energy, National Energy Technology Laboratory. Accessed September 28, 2022.

11Durant, V., Mansur, K., Ali, S., Levy, M., Nowakowski, T., & Redmond, M. (2018). Wisconsin Energy Statistics. (40th ed., 1975- 2015) Madison, WI: Wisconsin Office of Energy Innovation.

12U.S. Energy Information Administration. State Electricity Profiles. Wisconsin Electricity Profile 2018, Table 1. 2018 Summary Statistics (Wisconsin). Washington, DC, U.S. Energy Information Administration. Accessed April 21, 2020.