Geog. 143 -- Global Environmental Change

Exercise 4:  U.S. Greenhouse Gas Emissions Inventory

The United States is the largest overall emitter of greenhouse gases, and eighth-largest in terms of per-capita emission (behind Qatar, the United Arab Emirates, Singapore, Kuwait, Luxembourg, Bahrain, and Trinidad & Tobago).  As part of the U.S. commitments under the United Nations Framework Convention on Climate Change (UNFCCC), the U.S. Environmental Protection Agency prepares each year an inventory of greenhouse-gas sources and sinks from human activities (as opposed to the "natural" interactions between the terrestrial biosphere and the atmosphere).

The aim of this exercise is to explore parts of this inventory in order to get an idea of what human activities in the U.S. generate greenhouse gases and how those emissions and human-action-related sinks are changing over time.

The text and tables of the current GHG emissions inventory for the U.S. is at:

http://www.epa.gov/climatechange/emissions/usinventoryreport.html

(see the Executive Summary and Full Report .pdfs on that page).  The Full Report is rather large, and the Executive Summary usually contains enough information to get an idea of how emissions are changing.

NOTE:  The inventory usually gets updated in April.  It's possible that when you browse to the above pages, the 1990-2005 report that the exercise uses will have been replaced by a 1990-2006 version.  If that's the case the "current version" will contain another year's worth of data, and updates for some earlier years.  However, use the links below to the 1990-2005 summaries while doing the exercise.

In addition, there is a two-page "Fast Facts" summary available as a .pdf file, that also includes some conversion tables that help make sense of the units used to summarize GHG emissions:

http://www.epa.gov/climatechange/emissions/downloads06/06FastFacts.pdf

Before answering the questions, take a few minutes to browse through the Fast Facts summary and the "Executive Summary" of the inventory.  That chapter is available at:

http://www.epa.gov/climatechange/emissions/downloads06/06ES.pdf

The question below can be answered by simple inspection of the tables, but more efficiently by some simple plots that can be made using Excel.  To download or open a subset of tables that can help answer the questions, click on the following link, and depending on the particular browser you're using, you'll be asked to open or save the .xls spreadsheet (either is fine, but if you save the spreadsheet  you can use it later, e.g. by emailing it to yourself):

http://geography.uoregon.edu/bartlein/courses/geog143/labs/EPA-GHG-Inventory.xls

If you're not in a position to use Excel, there is also a printed version of the tables available as a .pdf file:

http://geography.uoregon.edu/bartlein/courses/geog143/labs/EPA-GHG-Inventory.pdf

1. Emissions and how they are changing

This part of the exercise examines the emissions of the main greenhouse gases (GHGs) and their changes over time.  Begin by clicking on the "Summary" tab in the worksheet (or by looking at page 9 of the .pdf).  The tables here summarize the total emissions from the four main sources, as well as the total "sink" of CO2 related to land-use changes.  (Remember that this inventory does not include the "natural" flow of carbon into or out of the terrestrial biosphere, only that related to human activities.)

Create two plots (or examine the table) before answering the question:

  • Plot the variation over time of the total emissions, the land-use change-related sink and the net emissions (total emissions - sink):

  1. Select row 2 (the row with the Year labels) by clicking on the row number.  (The cursor will change to a ° when you're in the right place.)

  2. Hold down the control (ctrl) key, and without letting it up, click on the row number labels for rows 7 (Total Emissions), 8 (Sinks), and 9 (Net Emission).  Rows 2, 7, 8, and 9 should now be selected.

  3. Click on Insert > Chart, and select as the standard chart type "Line", and as the chart subtype "Line with markers..."  (that should already be selected--it's the left-hand cell in the second row of example charts).

  4. Click on Finish.

  • Plot the variation over time in the major emissions sources and sinks:

  1. Select rows 2 through 6 and row 8, as in steps 1 and 2 above.  (Make sure row 7 is not accidentally selected.)

  2. Click on Insert > Chart, and select as the standard chart type "Column" and as the chart sub-type "Stacked Column" (it's the middle column of the first row of example charts).

  3. Click on Finish.

Q1:  How have U.S. GHG emissions varied over the interval 1990 through 2004?  (Have they remained constant, increased, decreased, etc.?)  Which influences net emissions more, total emissions or sinks?  Of the four major sources of GHG emissions, which is increasing the fastest?

2.  Changes in individual sources

The major categories of greenhouse gas emissions are in turn determined by a number of different sources or activities.  The year-to-year variations of these sources or activities are summarized in the Fast Facts .pdf and on the FastFacts tab of the .xls file, and the 1990-2004 changes appear on the "Changes" tab in the spreadsheet (or look at pp. 3 and 4 in the .pdf).  (This question can be answered by inspection of the table on the Changes tab.) 

Q2:  Which of the individual sources has increased the most over the 15 years represented by the data, in both absolute and relative (i.e. percentage) terms?  Which have decreased?  (Note that the "Land-Use Change and Forestry (Sink) absolute change is positive (130.3 Tg CO2 equivalent), and its relative change is negative (-14.3%) which means that the land-use change sink is decreasing in importance over time.  (Examine the "FastFacts" or "BySource" tab (or pp. 1-2 and 5-6 in the .pdf) to see this).

3.  Changes in emissions by sector

Greenhouse gas emissions are generated by a number of different broad sectors of the economy, like transportation or residential heating and cooling, and the relative importance of the different sectors is changing over time.  Switch to the "BySector" tab (or p. 7 of the .pdf)

  • Plot the variation over time of the emissions by major economic sector:

  1. Select rows 2 through 8.

  2. Create a "Line with markers" chart as before.

Q3:  Which sector shows the greatest increase over time and which the least?  (Be careful to not just compare the first and last values of the series--it's better to compare the first few years with the last few.)  What changes in the individual sectors might be contributing to these patterns of overall change?

4.  Changes in some economic, population, and emissions indicators

The relationship between the trends in greenhouse gas emissions and some of the large-scale "drivers" can be seen using the standardized data that appears on the "Trends" tab (or p. 8 of the .pdf).  In those data, the absolute values of the different indicators are are turned into relative values (i.e. percentages) by dividing by the 1990 values, to make them more easily comparable.  For example, the value 106.48 for the 2004 (global) atmospheric CO2 concentration (377 ppm) indicates that it is 6.48 percent greater than the 1990 value (354 ppm).

Create two plots (or examine the table) before answering the question:

  • Plot the variation over time of the GHG emissions, energy consumption, fossil-fuel consumption, electricity consumption, GDP and population. (Select rows 2-9, and create a "Line with markers" plot.)
  • Plot the variation over time of the GHG emissions per capita, energy consumption per capita, and GHG emissions per GDP unit.  (Select rows 2, and 10-12, and create a "Line with markers" plot.)

Q4:  Which is increasing faster, the "size" of the economy (GDP), energy consumption (total, electrical, fossil fuel), or population?  Describe the variations in GHG emissions per capita, total energy consumption per capita, and the GHG emissions per GDP unit.  Does this information support or contradict the idea that reducing GHG emissions would have a negative impact on economic growth?