COA_GHGInv_Full

CITY OF ASPEN CANARY INITIATIVE
and CLIMATE MITIGATION SERVICES
May 2009
AN UPDATE TO THE 2004 BASELINE

CLIMATE MITIGATION SERVICES
RICHARD HEEDE
Principal Investigator
heede@climatemitigation.com · www.climatemitigation.com
1626 Gateway Road · Snowmass, CO 81654 USA
970.927.9511 ofﬁce
970.343.0707 mobile
Copyright ©2009 CMS
This work was done July 2008 to April 2009
under contract with the City of Aspen.
CITY OF ASPEN PRINCIPAL CONTACTS
NOTE ON UNITS: Common U.S. units are used throughout. The spreadsheets present emissions results in both U.S. and metric units. Emissions
of methane and nitrous oxide are expressed in CO2 -equivalent terms (CO2 e). See Appendix A for conversions and emissions factors.
KIM PETERSON
Global Warming Project Manager
970.920.5071
kim.peterson@ci.aspen.co.us
MARTA DARBY
Data Analyst
970.920.5072
marta.darby@ci.aspen.co.us
City of Aspen
130 South Galena Street · Aspen, Colorado 81611 · U.S.A.
www.canaryinitiative.com

C I T Y O F A S P E N · C A N A R Y I N I T I A T I V E
1
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Scope and Emissions Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Transportation: Ground Transportation & Air Travel . . . . . . . . . . . . . . . . . . . . . . . . . 14
Buildings: Electricity, natural gas, & propane . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Other sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Reduction Efforts: In Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
PURPOSE, SCOPE, & EMISSIONS BOUNDARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Emissions Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Emissions Savings: Emission Reduction Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
CHANGES TO METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Commercial Air Travel: 2007 calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
General Aviation: 2004 baseline inventory revision . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Economics & Aspen’s Greenhouse Gas Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
In Perspective: Aspen’s Greenhouse Gas Emissions. . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Buildings: Electricity, Natural Gas, & Propane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Propane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Ground Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Air Travel & Aviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Other sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Pitkin County Solid Waste Center. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Nitrous Oxide Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

2
IN COMPARISON: KEY FINDINGS AND CASE STUDIES . . . . . . . . . . . . . . . . . . . . . . . . 55
Key Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Buildings: Electricity, Natural Gas, & Propane . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Other Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
ARE WE ON TRACK?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
APPENDIX A: CARBON FACTORS & COEFFICIENTS, CONVERSION FACTORS, NOTES . . . . . . . . 67
APPENDIX B: CONTACTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
APPENDIX C: WORKSHEETS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
FIGURES
Figure ES-1. Aspen emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure ES-2. Geographic emissions boundary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure ES-3. Major sources 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure ES-4. Major sources 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure ES-5. Electricity emissions and consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure ES-6. Air travel 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure ES-7. Ground transportation 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure ES-8. Buildings emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 1. Map of Aspen’s Emissions Inventory Boundary & primary GHG emissions sources . . . . . . . . . 22
Figure 2. Aspen emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 3. Emissions by greenhouse gas 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 4. Major sources 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 5. Major sources 2004 versus 2007, subcategories . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 6. Cost of energy 2004 versus 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 7. Buildings emissions 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3
Figure 8. Electricity, natural gas, propane emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . 36
Figure 9. Electricity emissions and consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 10. Electricity emissions factors 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 11. Electricity emissions by provider 2004 versus 2007. . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 12. Aspen Electric service territory map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 13. Natural gas consumption 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Figure 14. Transportation emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 15. Ground transportation emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 16. Air travel emissions 2004 versus 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Figure 17. Highway 82 and commuting emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 18. Vehicle type survey. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 19. Ground transportation 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Figure 20. Air travel and aviation emissions 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Figure 21. Aspen’s emissions 1998 to 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Figure 22. Aspen’s emissions 1998 to 2008 and achieving 2050 goal . . . . . . . . . . . . . . . . . . . . 59
TABLES
Table ES-1. Aspen’s GHG emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table 1. Emissions: Included and Excluded. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Table 2. GHG emissions 2004 versus 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 3. Consumption: Buildings and Transportation 2004 versus 2007 . . . . . . . . . . . . . . . . . . . 31
Table 4. Total Aspen GHG emissions in 2004 & 2007, 2008 (forecast), and 2020 (Canary target) . . . . . . 60
BOXES
Box 1. Climate change and greenhouse gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Box 2. Aspen’s “industrial” emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Box 3. Aspen Electric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Box 4. Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Box 5. Methane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Box 6. Municipal buildings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

5
Updating a greenhouse gas inventory is a team effort and requires the contributions of many individuals and
organizations. The City of Aspen’s Canary Initiative would like to thank the following individuals for committing
their time, energy, and support to the production of this greenhouse gas inventory:
Aspen’s Mayor Mick Ireland and the Aspen City Council approved funding and methodology for this report.
The City Council has also been supportive of Aspen’s efforts to de-carbonize its fuel mix for Aspen’s municipal
electric utility.
Rick Heede of Climate Mitigation Services is the chief inventorist of both this 2007 inventory and the City of
Aspen’s 2004 baseline greenhouse gas inventory. His thoroughness, methodology and attention to detail are
greatly appreciated.
Marta Darby with the City of Aspen’s Canary Initiative gathered and analyzed much of the data. She also wrote
much of this report.
Phil Overeynder and John Hines of the City of Aspen’s Public Works and Environmental Initiatives department
provided data on Aspen’s electricity mix and are both tireless champions committed to reducing the carbon
intensity of Aspen’s electricity supply.
Kim Peterson directs the City’s Canary Initiative and helped review and pull the final report together. Lauren
McDonell also helped with the data gathering. Lee Ledesma of the City’s Public Works Department helped make
all the financial pieces work and made sure everybody got paid.
John Katzenberger of the Aspen Global Change Institute reviewed the final report and methodology.
Jennifer Perez of Open Window Design provided graphic design services to produce the final report.
Jim Elwood of the Aspen/Pitkin County Airport educated the team on the airport’s 2006 greenhouse gas inventory
and provided review of this inventory.
Lind Lesmes and Jennifer Perez generated superb graphics.
The following individuals provided data without which this report could not have been produced: Dan Blankenship
and Kenny Osier (RFTA), Fred Brooks, Mark McKeller and Diana Sirko (Aspen School District), Dylan Hoffman,
Ellen Anderson and Timothy Knight (Pitkin County), Ellie Nieslanik (Valley Co-op), Landon Dean (T-Lazy Seven
Ranch), Matt Hamilton (Aspen Skiing Company), Craig Harvey (EPA’s National Vehicle and Fuel Emissions Lab),
John Kreuger, Steve Aitken, Bridgette Kelly, and Brian Flynn (City of Aspen), David Ulane and Stephen P.
Schultz (Aspen/Pitkin County Airport), Steve Casey and Craig Tate (Holy Cross Energy), Jill Jones (Municipal
Energy Agency of Nebraska), Natalie Shelbourn and Jerrad Hammer (Source Gas), Bart Levine (AM Gas), Jeff
Grebe (MecTric Engineering), Tad Peed (AmeriGas), Tom McBrayer (Cross Prone & Supply Propane Services),
ChrisHoofnagle(PitkinCountyLandfill),Dr.JeanBogner(Landfills+Inc.),TracyDillingham(AspenSanitationDistrict),
Scott Miller (Maroon Creek Club), and John Schied and Jeffrey E. Bowick (Aspen Valley Hospital).
Thanks also to the volunteers who assisted with the August 2008 traffic count: Aaron Reed, John Krueger,
CJ Oliver, Kim Peterson, John Eisler, Jannette Whitcomb, Ashley Cantrell, Ada Christensen, and Marta Darby.

7
The Aspen Greenhouse Gas Emissions Inventory, 2007 is the ﬁrst update to Aspen’s 2004 baseline emissions
inventory,1
providing insight into the impacts of reduction measures taken since 2004 and suggesting what
actions we must take to further reduce emissions. The report examines emission trends in various sectors, and
assesses whether emission reduction gains to date are on track to meet the City’s 30 percent emission reduction
target for 2020. Identifying the results of past actions enables the Aspen community to determine what next steps
must be taken to further mitigate climate change.
From 2004 to 2007, Aspen has reduced its emissions by 8.25 percent – about 2.8 percent per year. If Aspen
continues to reduce its emissions at this rate, the community will more than meet its 2020 target. Aspen reduced
its emissions from 828,648 tons CO2e in 2004 to 760,268 tons CO2e in 2007.2
The 2020 emissions target is
580,054 tons CO2e. (For more on emissions targets, see Are We on Track?) Some of the reductions in estimated
emissions are the result of revised methodology in emissions accounting rather than fundamental changes in
consumption patterns. (See Changes to Methodology.)
1 Heede, Richard (2006) Aspen Greenhouse Gas Emissions 2004, for the City of Aspen’s Canary Initiative, Climate Mitigation Services, 96
pp, 14 spreadsheets; www.climatemitigation.com
2 2004 total emissions were revised downward by 12,400 tons CO2e through a revision in how General Aviation emissions are calculated.
See “Changes to Methodology.”
TOTAL GREENHOUSE GAS EMISSIONS
Comparing 2004 to 2007
Tons CO2e
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
20072004
828,648
760,268
Figure ES-1. Aspen emissions 2004 versus 2007

8
Aspen has reduced its emissions in nearly every category – buildings and facilities, commuting and ground
transportation, air travel and general aviation – except for the County Landfill’s methane emissions, a result of
better data on such fugitive emissions becoming available in 2007.
Policies alone do not drive emissions reductions. The cost of energy also affects consumption. For example, when
gasoline costs increase, more people ride the bus. The data reflects this trend in the increase in bus ridership and
decrease in traffic. While fuel use and emissions associated with Roaring Fork Transportation Authority (RFTA)
buses go up, fuel use and emissions associated with commuting go down – decreasing more than that of RFTA’s
emissions increase.
Each of the three sectors (Transportation, Buildings, and Other Sources) is broken down to provide a more
detailed analysis. For example the Transportation sector, is broken into Ground Transportation and Air Travel,
both of which are sub-categorized further. The Buildings sector is divided according to zoning type: commercial,
residential, and municipal; as well as utility type: electricity, natural gas, and propane.
SCOPE AND EMISSIONS BOUNDARY
The scope of the update captures what Aspen’s community is responsible for directly, as well as the most
important indirect emissions sources that are attributable to the activities, buildings, and people of Aspen.
It follows the same protocol established in the 2004 baseline. In short, the 2007 inventory defines the carbon
footprint reasonably attributable to Aspen’s physical, cultural, and economic existence and the progress made
toward reducing emissions.
The 2007 update encompasses the same area analyzed in the 2004 baseline – all emissions sources within the
Emissions Inventory Boundary (EIB). Geographically, the boundary extends beyond the Aspen city limits to include
adjacent areas, such as Mountain Valley, Starwood, Red Mountain, the Aspen Airport Business Center, and others
that are tied closely to Aspen (Figure ES-2). Conceptually, the EIB includes sources such as energy use (natural
gas, propane, and electricity) from both residential and commercial buildings, including the indirect emissions
from such sources as coal-burning power plants that generate electricity for Aspen; road travel emissions from
commercial and personal vehicles; emissions from the Pitkin County Solid Waste Center; emissions from the
Aspen Skiing Company (excluding Snowmass); and emissions from air travel to and from Aspen and general
aviation aircraft that land and depart from the Aspen Pitkin County Airport, as well as commercial air travel at
nearby airports. (For more on inclusions and exclusions, see Purpose, Scope, & Emissions Boundary.)

9
82
Aspen
Ski Area
Buttermilk
Ski Area
Aspen
Highlands
Ski Area
Whitehorse Springs
& Starwood
Airport
Business Center
North 40
Highway 82
Traffic
Mountain
Valley
Aspen
School
District
Aspen
Valley Hospital
Pitkin County
Landfill
RFTA
Pitkin County
Airport & Air Travel
Emissions Inventory Area
City of Aspen Boundary
Ski Area Boundary
EMISSIONS INVENTORY MAP
ALSO INCLUDED
Natural Gas Use
Propane Use
Electricity Use
In-Town Vehicle Trafﬁc
Aspen-Related RFTA Bus Trips
Figure ES-2. Geographic emissions boundary

10
RESULTS
The amount of greenhouse gas emissions in and attributable to the Aspen-area in 2007 is 760,268 tons of
carbon dioxide equivalent (CO2e),3
down 8.25 percent from the 2004 baseline total of 828,648 tons CO2e and an
emissions decrease of 68,380 tons CO2e – a decline equivalent to the emissions of 2,680 average Aspen homes
(Figure ES-1).4
While Aspen’s total emissions decreased, consumption of electricity increased by 9.8 percent
and natural gas consumption increased by 3.7 percent. Aspen’s total energy use dropped by 5.5 percent from
2004 to 2007, largely a result of the decrease in fuel consumption in the Transportation sector.
The decrease in emissions is largely the result of the increase in the non-carbon fraction of the City of Aspen
Electric energy portfolio, up 28.6 percent over 2004, and the signiﬁcant decrease in Air Travel & Aviation
emissions, down 16.7 percent from 2004. Nearly all of Aspen’s emissions are carbon dioxide resulting from the
combustion of fossil fuels (95.7 percent), with the remaining 4.3 percent arising from methane (primarily from
the landﬁll) and nitrous-oxide gases from fertilizers.
3 Equivalent carbon dioxide (CO2e) is a standard unit of measure used to account for the global warming potential of a mix of greenhouse
gases, including carbon dioxide and methane.
4 The average Aspen home emits 25.51 tons CO2e per year, according the Sopris Foundation’s 2007 report, Anybody Home?: Energy
Consumption and Carbon Emissions from Second Homes in Aspen. The value is based on 2004 data and includes condos, duplexes/
triplexes, multifamily, and single-family homes.
MAJOR SOURCES OF EMISSIONS
2007
Air Travel & Aviation
36.4%
Ground Transportation
26.8%
Natural Gas & Propane
14.0%
Electricity
20.6%
Landfill
2.2% Nitrous Oxide
0.05%
Figure ES-3. Major sources 2007

11
The Inventory reﬂects everyday actions such as lighting homes and driving to the store. Of the three sectors
– Buildings, Transportation, and Other Sources – the Transportation sector contributes the most to Aspen’s
emissions (63.2 percent), as it did in the 2004 baseline inventory (65.6 percent) (Figure ES-3).
Source 2004 (tons CO2 ) 2007 (tons CO2 ) Change
Buildings -4.0%
Electricity 166,557 156,392 -6.1%
Natural gas & propane 106,768 106,084 -0.6%
Transportation -11.6%
Ground transportation 211,175 203,471 3.6%
Air travel: commercial 186,631 147,370 -21.0%
Air travel: general aviation 145,616 129,537 -11.0%
Other
Landfill & nitrous oxide 11,902 17,414 46.3%
Total 828,648 760,268 -8.3%
Greenhouse Gas Emissions Sources: 2004 vs. 2007
e e
Table ES-1. Aspen’s GHG emissions 2004 versus 2007
Note: 2004 General Aviation emissions revised from 157,856 to 145,616 tons CO2e and Aspen’s total
emissions from 840,888 to 828,648 tons CO2e.
MAJOR EMISSIONS SOURCES
Tons CO2e
180,000
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
2004
2007
Landfill
Methane
GA: JetsAir Travel
via Other
Airports
Air Travel
via Aspen
Tourist
Driving
Around
Town
CommutingNatural
Gas
Electricity
Figure ES-4. Major sources 2004 versus 2007

12
Emissions decreased in both the Transportation and Building Sectors – the two sectors that contribute the most
to emissions in Aspen. Emissions from the Transportation sector decreased by 11.6 percent; emissions from the
Buildings sector dropped by 4.0 percent; and emissions from Other Sources (landfill and nitrous oxide) increased
by 46.3 percent (Table ES-1, Figure ES-4). Other Sources plays the smallest role in Aspen’s overall emissions
at 2.3 percent of the total.
Of the six main categories analyzed in the emissions inventory – Electricity, Natural Gas & Propane,
Ground Transportation, Air Travel & Aviation, Landfill, and Nitrous Oxide Sources – Air Travel & Aviation
contributed the most to Aspen’s total emissions at 36.4 percent (40.1 percent in 2004), followed by
Ground Transportation at 26.8 percent (25.5 percent in 2004), and Electricity at 20.6 percent (20.1 percent in
2004) (Figure ES-3, Table ES-1).
From 2004 to 2007, the largest emission decreases were in the Electricity and Air Travel categories, with
smaller emission decreases from ground transportation and natural gas and propane use. While electric
emissions decreased (down 6.1 percent), electric consumption rose 9.8 percent from 2004 to 2007
(Figure ES-4).
The electric emissions decrease relative to its consumption increase is a result of the greening of the City of Aspen
Electric portfolio, which rose from 35.7 percent to 65.8 percent renewable (44.2 percent to 72.7 percent non-
carbon).5
The increase in Aspen Electric’s non-carbon portion of its fuel mix resulted in a significant decrease in
the utility’s carbon factor, thus resulting in fewer emissions per kilowatt hour of electricity consumed. Holy Cross
Energy’s carbon factor also decreased from 2004 to 2007.
Aspen Electric customers increased their electric use by 2.9 percent. Despite Aspen Electric customer’s increase
in consumption, their associated electric emissions decreased 51.5 percent, a result of the considerable increase
in the utility’s non-carbon sources of energy. Holy Cross customers increased their electric consumption by 12.8
percent. Emissions attributed to Holy Cross electricity use increased by 8.1 percent (Figure ES-5).
Air travel and aviation emissions decreased by 16.7 percent from 2004 to 2007, with notable drops in aviation
in and out of the Aspen-Pitkin County Airport. Commercial air travel emissions via Aspen decreased by 22.8
percent, by 16.0 percent via other regional airports, and private aviation jets and turboprops decreased by
11.0 percent (combined). Air Travel fuel consumption dropped by 16.6 percent (Figure ES-6). Contributing to
the decrease in emissions is the change in methodology used to calculate commercial air travel emissions (see
Updates to Air Travel & Aviation Methodology).6
Also contributing to the emissions decrease was the two-month
closure of the Aspen-Pitkin County Airport from April 9 to June 7, 2007.
5 Renewable energy sources include hydropower and wind. Non-carbon sources include nuclear, hydropower, and wind.
6 Some of the emissions reductions from Air Travel and General Aviation (personal and business jets and turboprops) arise from improved
accounting methods, and some reductions reflect decreased passenger air travel or fewer general aviation jets landing at Aspen in 2007
compared to 2004. Also, the airlines improved their average load factor (the percentage of occupied seats), which reduced the emission
factor per passenger-mile flown by Aspen’s 361,262 arriving and departing passengers.

13
9.1%
Aspen Electric:
Residential
1.8%
Aspen Electric:
Municipal
15.0%
Aspen Electric:
Commercial
40.4%
Holy Cross:
Residential
31.4%
Holy Cross:
Commercial
10
20
30
40
50
60
70
80
90
20,000 40,000 80,000 100,000 120,000
ThousandsofTonsCO2e
Megawatt Hours
60,000
ELECTRICITY EMISSIONS BY COMPANY AND SECTOR, 2007
Figure ES-5. Electricity emissions and consumption, 2007. The area of each circle represents
the carbon footprint of each utility’s end-use sector.
AIR TRAVEL AND AVIATION EMISSIONS
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
2004
2007
GA: Air
Ambulance
GA:
Piston
GA:
Turboprops
GA: JetsAir Travel
via Other
Airports
Air Travel
via Aspen
Figure ES-6. Air travel 2004 versus 2007

14
Transportation: Ground Travel & Air Travel
Greenhouse gas emissions from the Transportation sector arise from the combustion of gasoline, diesel, jet fuel,
and aviation gasoline.
Emissions from the Transportation sector represent 63.2 percent of Aspen’s total emissions. The 2007 inventory
indicates an 11.6 percent decrease in Transportation sector emissions over 2004, representing an emissions
decrease of 63,044 tons CO2e – the equivalent of 2,470 average Aspen homes. Fuel consumption also decreased
by 12.2 percent, corresponding to a drop in fuel use of 6.5 million gallons.
The Transportation sector is divided into two categories: Ground Transportation and Air Travel & Aviation.
Ground transportation emissions comprise 42.4 percent of the total emissions from the Transportation sector
(26.8 percent of Aspen’s total) (Figure ES-7); air travel and aviation emissions comprise 57.6 percent of the
sector’s total (36.4 percent of Aspen’s total) (Figure ES-6).7
From 2004 to 2007, ground transportation emissions decreased 3.6 percent, an emissions savings of about
7,700 tons CO2e. Air travel and aviation emissions decreased by 16.7 percent, reducing emissions by
55,340 tons CO2e from 2004.
7 Because air travel is an integral part of Aspen’s economy, both legs of air travel were included, as was done in the 2004 baseline
inventory.
MAJOR GROUND TRANSPORTATION EMISSIONS
Tons CO2e
140,000
120,000
100,000
80,000
60,000
40,000
20,000
SkiCo
Diesel & Gasoline
RFTATourist DrivingAround TownCommuting
Figure ES-7. Ground transportation 2004 versus 2007

15
Buildings: Electricity, Natural Gas, & Propane
Greenhouse gas emissions from the Buildings sector come from the generation of electricity and the burning
of natural gas and propane for heat. Energy use in buildings and facilities accounts for 34.5 percent of Aspen’s
emissions. From 2004 to 2007, emissions from buildings dropped by 4.0 percent – an emissions savings of
10,849 tons CO2e – roughly equal to 425 average Aspen homes.
The Buildings sector is divided into two categories: Electricity and Natural Gas & Propane. Electricity contributes
the most to emissions from the Buildings sector at 59.6 percent (20.6 percent of Aspen’s total emissions).
Natural gas and propane comprise 40.4 percent of emissions from the sector (14.0 percent of Aspen’s total
emissions) (Figure ES-8).
The Buildings sector also is subdivided into building type: Residential and Commercial & Municipal. Both of the
categories contribute roughly equally to Aspen’s emissions (Figure ES-5).8
This trend is consistent with that of
the 2004 baseline inventory.9
8 Residential buildings consumed 113 million kWh of electricity in 2007 (83,696 tons CO2e) and 957 billion cubic feet (Bcf) of natural
gas (52,599 tons CO2e). Commercial & Municipal buildings consumed 111 million kWh of electricity (72,696 tons CO2e) and 927 Bcf of
natural gas (50,965 tons CO2e). Commercial Municipal includes electricity used for street lighting, ski lifts, runway lighting, and wastewater
treatment.
9 In the 2004 baseline, natural gas provider Kinder Morgan (now SourceGas) assumed that natural gas for consumed for both the
Residential and Commercial & Municipal categories was equal. For the 2007 inventory, Source Gas did not make the 50-50 assumption,
and instead provided usage ﬁgures for both categories. AM Gas also supplies natural gas to commercial customers. As a result, in 2004
Commercial & Municipal buildings were responsible for 60 percent of the emissions associated with natural gas. In 2007, natural gas
emissions were 50.8 percent residential and 49.2 percent commercial and institutional. In 2004, electric consumption and emissions were
roughly equal between the two building types.
Tons CO2e
ELECTRICITY, NATURAL GAS, AND PROPANE EMISSIONS
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
Aspen Electric AM Gas Propane VendorsHoly Cross SourceGas
2004
2007
Figure ES-8. Buildings emissions 2004 versus 2007

16
Other Sources
Emissions from the Pitkin County Solid Waste Center and sources of nitrous oxide contributed the least to
greenhouse gas emissions in 2007, consistent with the 2004 baseline inventory.
Landfill. Landfill emissions consider the energy used onsite and fugitive methane emissions from the breakdown
of the buried wastes. Landfill emissions contribute to 2.2 percent of Aspen’s total. From 2004 to 2007, landfill
emissions increased by 47.5 percent, representing an emissions increase of 5,495 tons CO2e – the equivalent of
215 Aspen homes. Electricity usage, diesel and gasoline consumption, and methane all contributed to the rise
in emissions, with fugitive methane emissions increasing the most over 2004 (up 47.6 percent, 5,468 more tons
CO2e), a result of a 47.5 percent increase in the total amount of fugitive methane produced at the landfill. The
increase in methane emissions can be attributed to a better estimate of methane generation and leakage, based
on a 2007 report.10
Nitrous oxide. Nitrous-oxide emissions arise from nitrogen-based fertilizers applied to City- and privately-owned
golf courses, athletic fields, parks, and backyards. They account for 0.05 percent of Aspen’s emissions. From
2004 to 2007, nitrous oxide emissions rose by 5.4 percent, up 17 tons CO2e.
Although the amount of nitrous oxide applied is relatively small, its effect as a greenhouse gas is 296 times
stronger than carbon dioxide.
REDUCTION EFFORTS: IN REVIEW
Since 2004, a number of steps have been taken to reduce Aspen’s greenhouse gas emissions. Of the actions
adopted since the 2004 inventory, increasing the renewable portfolio of the City’s electric utility and enhancing
mass-transit options have had the greatest impact on reducing emissions.
Increasing the City of Aspen Electric’s energy portfolio to 72.7 percent non-carbon in 2007 (up from 44.2
percent in 2004).
Result: Decrease in emissions associated with Aspen Electric, despite the increase in electric consumption.
In the absence of the strides made toward a more renewable power supply, emissions associated with
Aspen Electric would have increased by 4 percent to 41,350 tons CO2e instead of declining to 19,298
tons CO2e.
Increasing ridership on RFTA’s buses to 2.79 million riders using city shuttles, Music Associates of Aspen and
skier buses, as well as valley routes. RFTA also increased its fleet of hybrid buses to 11.
Result: While emissions attributed to RFTA increased from 2004 to 2007, the service “saves” emissions by
keeping bus riders from using personal vehicles. RFTA saves an estimated 961,000 gallons of gasoline
and keeps 9,416 tons CO2e from being emitted.
10 Golder Associates (2007) Landfill Gas Evaluation of the Pitkin County Solid Waste Center, Lakewood CO, 41 p., www.golder.com

17
CONCLUSION
Since 2004, Aspen’s emissions have decreased by 8.25 percent, largely thanks to the greening of the City of
Aspen’s municipal electric utility and the significant decrease in Air Travel & Aviation emissions. Despite the
decrease in electric emissions, electric consumption increased by 9.8 percent (2.9 percent for Aspen Electric
and 13 percent for Holy Cross Energy).
The two main drivers of reduced air travel emissions are the change to the commercial air travel load factor
calculation and, to a smaller extent, the two-month closure of the Aspen-Pitkin County Airport. While neither
of these factors represents a real reduction in air travel attributable to our community, emissions decreased
substantially.
So far, we are on track as a community to meet our greenhouse gas reductions goals. However, some of the
“low-hanging fruit” has already been picked. Early indications using QuickTracker data from 2008 reveal that
emissions are likely to increase 1.9 percent from 2007, largely as a result of increased air travel.11
Meeting our community-wide 2020 goals will require deliberate and committed action from Aspen’s residents,
visitors, businesses, government, and events to substantially reduce that portion of the energy they consume
from carbon based sources. Electricity and natural gas usage must decline rather than rise and the electric
utilities serving the Aspen-area must continue to expand their renewable-energy portfolios. Residents and visitors
also must utilize mass transit with even greater frequency. RFTA’s service expansion plans are poised to meet a
significant increase in demand. Finally, until viable biofuels are developed for aviation and the carbon intensity of
air travel can be mitigated, aviation emissions will likely remain high.
The City of Aspen, through de-carbonizing its electric utility, and RFTA, for its extensive transit network, have
led our community toward a decrease in emissions. Now it’s time to take the next steps – reducing consumer
demand for energy through abundant and profitable energy efficiency measures and continuing to add more
clean energy sources.
11 The QuickTracker is an emissions calculation tool that provides an estimate of emissions based on traffic counts, new building, and air
travel.

19
PURPOSE
In March 2005, the Aspen City Council passed a resolution creating the Canary Initiative and directing the City
Manager to “establish a greenhouse gas (GHG) emission inventory for the City of Aspen that quantifies GHG
emissions and is capable of tracking progress or lack of progress quantitatively in reducing emissions for all
sectors of the Aspen economy.”12
In 2006, the first Aspen-area emissions inventory was completed, establishing
a baseline with 2004 data.
This inventory, based on 2007 data, is the first update to the 2004 baseline emissions inventory. It seeks to
answer two questions: How has the carbon footprint attributable to Aspen’s physical, cultural, and economic
existence changed from 2004 to 2007, and what are the primary drivers of those changes?
The 2007 update follows the same methodology as the 2004 baseline and is fully documented with respect to
sources and methods so that future inventories can accurately assess progress or regress in reducing emissions.
The complete core set of 16 spreadsheets (Appendix C) details the methods and results for each emissions
source as well as the data, calculations, caveats, formulas, and assumptions used in the Aspen Greenhouse Gas
Emissions Inventory, 2007.
SCOPE
The first inventory of Aspen’s citywide greenhouse emissions was conducted for 2004. The scope and boundary
of the 2007 inventory follows the same guidelines established during the 2004 baseline. While the inventory is
comprehensive, not all emissions sources are considered (Table 1).
12 The resolution states, in part “Therefore: […] 6. Establish a greenhouse gas (GHG) emission inventory for the City of Aspen that
quantifies GHG emissions and is capable of tracking progress or lack of progress quantitatively in reducing emissions for all sectors of the
Aspen economy. Said emission inventory shall be of sufficient quality, at a minimum, to qualify for consideration by the Chicago Climate
Exchange membership and participation. 7. Establish, with the assistance of the Aspen Global Warming Alliance, periodic GHG reduction
goals for the City of Aspen, and various sectors of the community. 12. Prepare and present for City Council consideration, a plan to reduce
GHG emissions from transportation and vehicular traffic in Aspen. 13. Prepare appropriate legislation for City Council consideration
that would reduce energy consumption in multi-family and commercial buildings in the City of Aspen. 14. Establish a comprehensive,
aggressive and sustained public awareness campaign on global warming for the Aspen-area that is readily capable of duplication for
other regions of the state or country. The public awareness campaign shall, at a minimum, include the publication and distribution of
educational materials explaining the reason for the City’s adoption of the Canary Initiative, an objective explanation of the global warming
phenomenon, and an objective recitation of the potential threat of climate change to the Aspen economy and way of life.”

20
Greenhouse gases are trace amounts of
natural and synthetic gases that trap heat
in the Earth’s atmosphere, reducing the
Earth’s ability to radiate heat to outer space
and thereby changing the Earth’s climate.1,2
TEMPERATURE RISING. In the United
States, the average temperature has risen
by more than 2˚F over the past 50 years, a
change that is the result of human activity.
The warming trend is expected to continue;
how much more depends on current and
future greenhouse gas emissions. Globally,
temperaturesareexpectedtoriseby2to10˚F
by the end of the century, and the United
States is likely to experience an increase
greater than the global average. If human-
induced greenhouse gas emissions are cut
significantly, the increase in temperature
will be closer to 2˚F; however, if emissions
continue at or near current levels, average
global temperatures will increase to the
upper end of the range.1,2
CLIMATE CHANGE IS NOT UNIFORM.
Climate change is not a uniform
phenomenon, and its affects already are
being experienced in the United States.
Over the past 50 years, precipitation has
increased an average of 5 percent, making
wet areas wetter, while dry areas have
become drier. This trend is projected to
continue. Other changes that are resulting
from the warming climate include stressed
water resources, increased intensity of
hurricanes, sea-level rise, decreased sea-
ice coverage, altered wildlife migration
patterns, regional changes in rain and
snowfall, earlier peak streamflows, and
increases in air and water temperatures. As
the climate continues to warm, the impacts
are expected to increase as well.1,2
PRIMARY GREENHOUSE GASES. The
mostimportantgasesfromaclimate-change
perspective are carbon dioxide, methane,
nitrous oxide, and halocarbons, a class of
industrial compounds such as refrigerants,
blowing agents, and propellants. Aspen’s
greenhouse gas emissions inventory focuses
on carbon dioxide from the combustion
of fossil fuels such as coal and petroleum
(gasoline is 86 percent carbon by weight);
methane from coal mining, natural
gas systems and anaerobic digestion of
organic wastes in the landfill (in which
microorganisms break down material in
the absence of oxygen); and nitrous oxide
from nitrogen-based fertilizers applied to
golf courses and backyards.
ASPEN VERSUS UNITED STATES. Carbon
dioxide comprised 95.7 percent of Aspen’s
2007 emissions inventory, compared to 82.7
percent of U.S. emissions. Aspen’s methane
emissions are 4.3 percent of the total,
compared to 9.6 percent nationally; nitrous
oxide emissions in Aspen are less than 0.05
percent compared to 5.3 percent nationally.
Aspen’s emissions are reported as carbon
dioxide or its equivalent of methane or
nitrous oxide (CO2e).3
For more information about climate
change, visit www.epa.gov/climatechange.
For specific impacts on the United States,
download the report Global Climate
Change Impacts in the United States at
www.climatescience.gov.
1 US Climate Change Science Program 1.2.
(see references section)
2 US Climate Change Science Program 2.2.
(see references section)
3 EIA (2008) Emissions of Greenhouse Gases in
the United States in 2007, U.S. Department of
Energy.
Box 1. Climate change and greenhouse gases

21
Table 1. Emissions: included and excluded
EMISSIONS SOURCES: INCLUDED VERSUS EXCLUDED
SOURCES INCLUDED EXCLUDED
CARBON DIOXIDE
Buildings Electricity use X
Buildings Natural gas use X
Buildings Propane use X
Transportation Gasoline, diesel fuel use X
(eg., in-town driving, tourists, commuting)
Transportation Gasoline and diesel fuel use X
(snowmobiles, groomers, RFTA, school busses, other)
Transportation Jet fuel use, Aspen X
(both legs of air travel, commercial and private)
Transportation Jet fuel use, other regional airports X
(both legs of air travel, commercial)
Transportation Aviation gasoline, Aspen (itinerant and local aircraft) X
Landfill Electricity use X
Landfill Diesel use X
Resources (other) Harvesting, processing, transportation of materials X
(building materials; agriculture, meat, and
beverages; fuel transport)
Resources (other) Extraction, harvesting, fabrication, processing, X
manufacturing (appliances, vehicles, clothing, fertilizers),
Wood burning X
METHANE
Buildings Mining coal for power generation, attributed to Aspen X
Buildings Drilling for natural gas and propane attributed to Aspen X
Landfill Decomposition of organic materials X
Resources (other) Harvesting, processing, transportation of materials X
(building materials; agriculture, meat, and
beverages; fuel transport)
Resources (other) Extraction, harvesting, fabrication, processing, X
manufacturing (appliances, vehicles, clothing, fertilizers)
NITROUS OXIDE
Nitrogen-based fertilizer use X
Resources (other) Nonlocal application of fertilizers for use in agriculture X
OTHER
Halocarbon and related refrigerants & foam-blowing agents X
Radiative forcing from high-altitude jet aircraft operations X

22
EMISSIONS BOUNDARY
Geographic boundary. The geographic boundary is nearly identical to the City of Aspen’s Urban Growth Boundary
(UGB), but also includes Starwood and the White Horse Springs section of the McLain Flats residential areas.
The Emissions Inventory Boundary (EIB) covers the residential areas within and contiguous to the Aspen city
limits such as Red Mountain, Mountain Valley (on the southeastern edge of town), Highlands, Buttermilk West,
the Aspen-Pitkin County Airport, the Aspen Airport Business Center, and North Forty (Figure 1). The EIB also
extends beyond the UGB to include the electricity used to run lifts and facilities on Aspen Mountain, Aspen
Highlands, and Buttermilk ski areas because the base facilities and many lifts are within the EIB. The fuel used
by Aspen Skiing Company’s snowmobiles, snowcats, and other equipment also is included, as is natural gas used
in its buildings and facilities (with the exception of Snowmass).
Figure 1. Map of Aspen’s Emissions Inventory Boundary & primary GHG emissions sources
82
Aspen
Ski Area
Buttermilk
Ski Area
Aspen
Highlands
Ski Area
Whitehorse Springs
& Starwood
Airport
Business Center
North 40
Highway 82
Traffic
Mountain
Valley
Aspen
School
District
Aspen
Valley Hospital
Pitkin County
Landfill
RFTA
Pitkin County
Airport & Air Travel
Emissions Inventory Area
City of Aspen Boundary
Ski Area Boundary
EMISSIONS INVENTORY MAP
ALSO INCLUDED
Natural Gas Use
Propane Use
Electricity Use
In-Town Vehicle Trafﬁc
Aspen-Related RFTA Bus Trips

23
Conceptual boundary. The conceptual emissions boundary is broader than the geographic boundary, encompassing
emissions within the geographic boundary (direct emissions) as well as those that are attributable to Aspen but
occur elsewhere (indirect emissions).
Direct emissions. Direct emissions considered in the inventory include: carbon-dioxide emissions from
natural gas and propane consumption; carbon dioxide emissions from fuel used for ground transportation
within the boundary; methane emissions from Pitkin County Solid Waste Center; and nitrous oxide
emissions from fertilizers applied to local golf courses, backyards, and athletic fields.
Indirect emissions. Indirect emissions considered in the inventory include: carbon dioxide emissions
from fossil fuels combusted in power plants that supply electric power to Aspen (primarily located in
Colorado), as well as methane emissions from the coal mines supplying those power plants; methane
emissions from leaks associated with the supply of natural gas;13
energy-related emissions from the
Pitkin County Solid Waste Center;14
carbon dioxide emissions from air travel (both coming to and leaving
from Aspen); and carbon dioxide emissions from fuel used for commuting, tourist driving, and RFTA
outside the boundary.
Aspen versus other cities. Aspen’s inventory includes emissions from fuel burned in cars and aircraft that bring
residents and visitors to and from Aspen. It is the first city to include both directions of air and commuting travel
(coming to and leaving from Aspen) in its emissions inventory (Box 2). Aspen’s tourist-based economy depends
on visitors staying in town as well as traveling to Aspen; thus, air- and ground-travel emissions are attributable to
the community.15
Transportation-related fuel and emissions are calculated from points of origin, whether Sydney
or Carbondale, rather than just the emissions that occur within the Aspen area.16
Within the boundary: included emissions. The following emissions sources are included in the inventory, either
because they occur directly within the geographic boundary or indirectly outside the boundary yet are attributable
to the Aspen-area (Table 1). For information regarding how the emissions estimates are made, refer to Changes
to Methodology and the 16 worksheets in Appendix C.
13 An industry-wide fugitive methane emissions rate — from natural gas production, processing, and transportation — is applied to
Aspen’s gas consumption. It is not an estimate of SourceGas’s own fugitive emissions, e.g., the pipeline breaks that occur at construction
sites, because of system failures, and replacing old pipelines. Such leaks have not, to our knowledge, been quantified. In any case, Aspen
is attributed a share of the industry-wide emissions in proportion to Aspens’ consumption of natural gas.
14 Since the landfill receives waste (and recyclables) from within Aspen’s emissions boundary as well as other areas of Pitkin County, we
allocate emissions on the basis of estimated materials flow to the landfill originating in Aspen.
15 The emissions are allocated on the basis of arriving and departing passengers who are flying to Aspen (70 percent), excluding the
remainder who use the Aspen Pitkin Airport but do not live or are not visiting Aspen, e.g., Snowmass Village, Carbondale, or other local
destinations.
16 The Aspen Global Warming Alliance considered attributing half or even zero air travel, commuting, and tourist driving emissions to
Aspen — ostensibly to avoid counting emissions that other communities where Aspen-bound workers or visitors live could include if they
did their own inventories — but Alliance members concluded that our inventory should include both legs of such travel in order to fully
account for Aspen’s impact on the global climate (see Box 2).

24
In brief, the major inventory emissions sources include:
1. Carbon-dioxide emissions from the use of electricity in buildings and facilities within the
boundary, plus related methane emissions from mines supplying coal to power plants generating
the power consumed in Aspen;
2. Carbon-dioxide emissions from the combustion of natural gas and propane in buildings within
the emissions boundary. This includes gas used in residential, commercial, and public buildings
and facilities (e.g., in homes, businesses, schools, government buildings, pools, and heated
driveways);
3. Methane emissions from the U.S. natural gas industry in proportion to the amount of natural gas
supplied to Aspen customers by natural gas and propane vendors;
4. Carbon-dioxide emissions from combustion of gasoline and diesel fuel within the boundary,
including in-town driving. This includes personal and commercial vehicles, trucks, RFTA buses
serving City routes, school buses, and City and County vehicles such as snowplows and police
cruisers used within Aspen’s emissions boundary;
5. Emissions from fuel used in commuting by Roaring Fork Valley residents who work in Aspen
but live downvalley, RFTA’s valley routes, as well as emissions from commercial and industrial
vehicle travel (e.g., by plumbers, couriers, and dump trucks on Highway 82);17
6. Emissions from fuel used in ground transportation of tourists and visitors;
17 Vehicle travel and related fuel consumption on Highway 82 inbound or outbound from Aspen is based on trafﬁc counters at Castle
Creek Bridge and upon a survey of vehicle types entering Aspen.
Most municipal inventories include
emissions from industries and businesses
within their boundary. Aspen’s main
economic engines – its industries – are
tourism and second homeownership, both
of which involve a great deal of travel, and
thus fuel use and carbon emissions.Tourism
and related commerce are fundamental to
Aspen’s quality of life and economy.
Visitors who travel by car or commercial
or private aircraft are all included in the
inventory. Both travel to and from Aspen
is included to acknowledge Aspen’s role
as a tourist destination. Energy used in
all homes, restaurants, hotels, clubs, retail
stores, and tourism-related commerce
and industry (including the Aspen Skiing
Company) is included in the inventory.
ASPEN’S “INDUSTRIAL” EMISSIONS
Box 2. Aspen’s “industrial” emissions

25
7. Emissions from commercial and personal/business aircraft transporting visitors and residents to
and from Aspen;
8. Emissions from commercial air travel by visitors and residents bound for or departing from Aspen
as well as travelers using other regional airports (Eagle, Grand Junction, and Denver);
9. Emissions from locally-based and itinerant single- and twin-engine piston aircraft;
10. Emissions from fuel used by snowmobiles, groomers, construction and excavation equipment,
and miscellaneous gas-powered contraptions (e.g., lawnmowers, snow-blowers, leaf-blowers);
11. Electric- and diesel-consumption emissions at the Pitkin County Solid Waste Center, plus methane
emissions released from the decomposition of organic materials buried at the site (apportioned to
Aspen based upon an estimate of the waste originating within the EIB);
12. Nitrous-oxide emissions from the use of nitrogen-based fertilizers (e.g., on golf courses, backyards,
and city parks and athletic fields).
Beyond the boundary: excluded emissions. Like any other town in the United States, Aspen draws resources
and thus energy and emissions from around the world – e.g., cement from Utah, hardwoods from Brazil,
water from Fiji. Aspen’s food-related carbon footprint has a similar global range.18
While Aspen depends on
such resources for its economic vitality and connectivity, emissions from resource extraction and emissions
from fabrication and delivery of these goods and materials are not included in the Aspen Greenhouse Gas
Emissions Inventory, 2007, consistent with the 2004 baseline.19
Emissions sources not attributed to Aspen include:
1. Emissions from harvesting, processing, manufacturing, or transportation of construction materials
(e.g., lumber, concrete and cement, steel, copper, marble, ornamental rock, gypsum, insulation
materials, paints and finishes, windows, roofing materials, and tropical woods);
2. Emissions from extraction, harvesting, fabrication, processing, or manufacturing of resources
(e.g., appliances, vehicles, aircraft, backhoes, heating and cooling equipment, water heaters,
snowmobiles, clothing, leather, medical imaging equipment, computers, furnishings, and skis);
3. Emissions from the extraction and production of other manufactured goods and basic materials
indirectly supporting Aspen’s economy (e.g., asphalt for road construction20
steel and other metals
used in appliances, vehicles, buildings, and infrastructure; industrial chemicals and petrochemicals
for paints, waxes, cleansers, and lubricants);
18 The average morsel of food travels 1,200 miles from field to table, according to the U.S. Department of Defense (undated) U.S.
Agriculture: Potential Vulnerabilities, from Durning, p. 73.
19 A small proportion of the transportation energy and emissions are included for in-valley and in-city delivery only.
20 Sand and gravel for road construction and concrete is produced locally but outside the emissions boundary, i.e., in Carbondale and
Woody Creek.

26
4. Emissions from the production of other processed materials (e.g., fertilizers, consumer chemicals,
pharmaceuticals, plastics, glass, newsprint, paper, containers, and packaging);
5. Emissions from the transportation of the foregoing materials, goods, and equipment (often
transported thousands of miles);
6. Emissions from the food and beverage industries (e.g., planting and/or harvesting of basic
agricultural products, vegetables, and fruits; foods and beverages processing; and packaging);
7. Emissions from the meat, fowl, and fish industries (e.g., energy used for ranching, poultry farming,
and fishing to the extent these facilities fall outside the EIB; and energy consumed in energy-
intensive processing, refrigeration, and transportation — often in refrigerated trucks or air freighted
for required freshness);21
8. Methane emissions from the meat, poultry, and agricultural sectors (ruminant animals and animal
manure emit large quantities of methane gas);22
9. Halocarbon and related refrigerants and foam blowing agent emissions;23
10. Nitrous-oxide emissions from agriculture and industry (other than local fertilizer applications);
11. Emissions from the oil and natural gas industries (e.g., exploration, production, transportation,
refining, and delivery of gasoline, diesel, and jet fuel).24
Fugitive methane from the natural gas,
propane, and coal mining/power generation industries are included;
12. Emissions from energy consumption from refineries, carbon-dioxide venting, and flaring in the
natural gas industry;
13. Carbon-dioxide emissions from wood burning.25
13. Radiative forcing (CRF) factor from the fuel emissions and vapor trails of aircraft operating at
high altitude.
21 Minor parts of the related energy inputs and emissions have been captured in this inventory, e.g., local trucking of foods in
transportation, operation of local groceries, and cooking energy in local homes and restaurants. As an indication of the scale of the ignored
energy inputs, Durning, p. 69: “The consumer food chain in its entirety uses about 17 percent of all energy; 3 percent for livestock
production, 3 percent for other types of agriculture, 6 percent for food processing and packaging, and 5 percent to transport, sell,
refrigerate, and cook the food and to wash the dishes afterwards.” Durning, p. 69. The greenhouse gas contribution will be far higher than
17 percent of energy inputs, given the methane and nitrous emissions from the various food chains.
22 Methane gas from animal digestion and wastes contribute 2.5 percent of total U.S. emissions. EIA (2005).
23 Nationally, halocarbons, bromines, sulfur hexafluoride, and related compounds comprise 2.1 percent (U.S. Energy Information
Administration) to 11 percent (Heede) of total domestic greenhouse gas emissions. The principal reason for their exclusion is the low
incidence of air conditioning in local buildings, but this use is increasing. Also, use of vehicle air conditioning is nearly universal, as are
commercial and residential refrigerators and freezers. Most such equipment has slow leaks, and even though it is Federal law to carefully
recover chlorofluorocarbons (CFCs) when replacing refrigerants, leakage is common. CMS recommends that halocarbons be included in
any update or extension of this inventory.
24 Emissions from exploration, production, transportation, refining, and delivery of gasoline, diesel, and jet fuel adds 19-27 percent to
the emissions from their combustion alone (as considered in the inventory). Wang (2001). A life-cycle assessment of gasoline concludes
that upstream emissions from gasoline is 27 percent above combustion emissions, and diesel (since the fuel requires less refinery energy)
emits 19 percent more; Delucchi (2003).
25 While wood burning is considered a carbon-neutral heating source, CMS recommends that its related emissions be included, at least
partially. Wood burning has declined sharply over the last several years, but likely remains a relatively small emissions source (CMS).

27
EMISSIONS SAVINGS: EMISSION REDUCTION MEASURES
Several emission reduction measures have been quantified, most of which are reflected in the emissions
calculations. Such reduction measures include the use of biodiesel by RFTA and the Aspen Skiing Company and
the lower carbon intensity of local electric utilities. Additional savings have been calculated for reference only,
and are not deducted from Aspen’s total emissions. Renewable and non-carbon electricity generation is included
in the emissions calculations for the power sector (see “Electricity carbon factor” worksheet, Appendix C).
Savings resulting from emission-reduction measures have been estimated for RFTA’s public transportation
services and the recycling program at the Pitkin County Solid Waste Center (the same two examples considered
in the 2004 inventory). As in the baseline inventory, the fuel and electricity inputs to RFTA’s bus fleet and to the
Pitkin County Solid Waste Center are included in the inventory.
1. Public transportation. RFTA’s buses reduce vehicle use, thereby lowering overall commuting
emissions. From 2004 to 2007, RFTA’s fuel use and emissions increased 40 percent to 4,395 tons
CO2e, while ridership increased from 2.07 to 2.79 million riders attributed to Aspen routes.26
These
avoided car trips save an estimated 18.4 million vehicle-miles, 0.96 million gallons of fuel, and
9,416 tons CO2e. These savings are not deducted from the inventory since the inventory accounts
for actual emissions from both buses and cars. Increased RFTA emissions are viewed as a “success”
when coupled with decreased vehicle emissions.
2. Recycling and composting. Aspen’s recycling program saves energy and reduces emissions.
Recyclable materials, including glass, metal, newsprint and cardboard, reduce the demand for virgin
forms of these products. The Pitkin County Solid Waste Center’s composting program decreases the
amount of wood, brush, and dirt buried in the landfill, thereby reducing methane emissions. We
estimate that the landfill’s recycling of 5,502 tons of glass, aluminum, paper, newsprint, etc. reduces
emissions by 9,161 tons CO2e. This is estimated to illustrate the climate-related savings from local
recycling efforts, and is not deducted from the inventory. The rate of recycling in the City of Aspen
is about 18 percent.27
These savings are not deducted from the inventory because emissions from
providing the material inputs to Aspen-area consumers are not included in the inventory.
26 A technical improvement was made to the 2007 inventory in data collection for RFTA’s ridership. Interviews with RFTA CEO Dan
Blankenship resulted in a higher proportion (71.6 percent in 2007 versus 39.1 percent in 2004) of riders on valley routes attributed to
Aspen. RFTA’s increased use of biodiesel (13.4 percent in 2007 versus 5.0 percent in 2004) tempered emissions increases.
27 The recycling rate is the total weight of recycled materials divided by the total weight of recycled materials plus the total amount of
waste generated. City of Aspen 2008 Recycling Report, www.aspenpitkin.com/uploads/Final%202008%20report.pdf

28
Aspen also has taken steps to reduce fuel-related transportation emissions by using biodiesel. RFTA and the
Aspen Skiing Company use biodiesel in at least part of their fleets:
1. RFTA’s diesel fuel is 13.4 percent biodiesel when averaged over all of 2007. The carbon coefficient
for RFTA’s diesel fuel is reduced from 22.38 (conventional diesel) to 20.03 pounds CO2 per gallon,
compared to RFTA’s 2004 biodiesel value of 21.51 pounds CO2 per gallon.28
2. Aspen Skiing Company used 20 percent biodiesel in 2007. The company is currently phasing out
the use of biodiesel.29
Aspen has several other programs that significantly reduce emissions. Also in the “savings” category but not
quantified:
1. Local consumer and City of Aspen generation and procurement of renewable sources of electricity
(e.g. solar PV and solar hot water systems).
2. The City and County’s Renewable Energy Mitigation Program (REMP) that invests fees, collected
based on excessive energy use in large homes, in energy-efficiency and renewable-energy measures
in both public and nonprofit projects throughout Pitkin County.
3. Cutting-edge energy building codes promulgated throughout Pitkin County have and continue
to keep thousands of tons coal and natural gas in the ground and thus thousands of tons of
carbon dioxide out of the atmosphere. These savings are not quantified, since we are accounting for
actual and measurable emissions, but a back-of-the-envelope calculation suggests that if Aspen’s
residential and commercial buildings were 20 percent less efficient then the community would emit
on the order of 50,000 tons additional tons CO2e per year – the equivalent of about 1,960 average
Aspen homes.30
4. Everyday actions by residents and business-owners that save fuel in buildings and transportation,
including improving the energy efficiency of their homes and buildings and carpooling or walking to
work.
28 CMS applies the net carbon savings of 78.4 percent from the biodiesel life cycle assessment in National Renewable Energy Laboratory
(1998) Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus, 314 pp.
29 Aspen Skiing Company website, viewed Apr09.
30 Aspen’s emissions from electricity, natural gas, and propane consumption totaled 262,475 tons CO2e in 2007, nearly all of it in
buildings.

29
The methodology for the 2007 inventory replicates that of the 2004 inventory. Where better data is available
some technical improvements have been made to most accurately reflect “state of knowledge” in emissions
quantification. Improvements have been made to how Air Travel & General Aviation emissions are calculated in
the 2007 inventory. Where appropriate, the 2004 inventory results have also been revised.
COMMERCIAL AIR TRAVEL: 2007 CALCULATION
The 2004 inventory used the U.S. domestic fleet average fuel consumption per passenger-mile for all domestic
and international air travel to and from Aspen31
to calculate air travel emissions. This fuel factor, however, did not
fully account for the differences between international, domestic, and regional (e.g. Denver to Aspen) travel. The
calculation for the 2007 inventory was revised to more fully account for these differences, using fuel and emission
factors appropriate to the three segments of travel (international, domestic, and regional). The 2004 inventory
results were not revised to reflect this change in calculation methodology.
GENERAL AVIATION: 2004 BASELINE INVENTORY REVISION
Of important note is an update to the 2004 baseline based on revised data available for air taxi operations. It was
discovered that in 2004, some air taxi operations were included in general aviation when they should have been
counted under commercial aviation as air carrier operations. New data available from Aspen/Pitkin County Airport
operations justified this change in data classification. The revision affects 2004 general aviation emissions as
well as Aspen’s total emissions for that year.32
General aviation emissions were revised to account for the portion
of commercial air carrier operations counted as air taxi operations in the 2004 baseline inventory.33
Emissions
from air travel on commercial aircraft are not affected. Commercial air travel emissions are based on passengers
enplaning and deplaning at Aspen-Pitkin County Airport; those data are unchanged. The report compares 2007
values to the revised 2004 emissions.
31 Fuel and emissions per passenger-mile flown is typically higher for shorter flights and smaller aircraft than for longer flights using larger
aircraft, since the take-off and climb phases require more fuel per minute than does cruise flight. CMS accounts for these factors and for
the higher load factor (fraction of seats occupied) in revising the methodology for 2007.
32 In calculating the fuel and emissions from personal and corporate jets landing and taking off at the Aspen-Pitkin County Airport for
2007, it was discovered that Air Taxi operations, as classified by the Federal Aviation Administration (FAA), include a number of flights
by air carriers operating aircraft with seating capacity of 60 passengers or less are classified as “Air Taxi” operations by the FAA. Thus,
operations by Mesa airlines, which operates 37-seat Dash-8s for United, were counted as Air Taxi operations in 2004. This correction was
made for the 2007 inventory; the 2004 baseline also was revised.
33 As revised, Aspen’s total aviation operations decreased from 44,022 landing and takeoffs (LTOs) in 2004 to 42,348 in 2007. Of these,
air carrier operations (as revised above) increased from 7,878 LTOs in 2004 to 9,500 LTOs in 2007; total general aviation operations
(revised) decreased from 36,144 LTOs in 2004 to 32,848 LTOs in 2007. Air Taxi operations were reduced by 2,645 arriving and departing
Mesa flights, reducing the 2004 Air Taxi operations to 9,823 LTOs. This reduced General Aviation’s jet and turboprop emissions in 2004
from a combined 156,643 tons CO2e to 144,403 tons CO2e. Total 2004 Air Travel & General Aviation emissions were reduced from
344,487 to 332,247 tons CO2e. Aspen’s total 2004 emissions were reduced by 12,240 tons CO2e (from 840,888 to 828,648 tons CO2e).

30
In 2007, Aspen’s direct and indirect greenhouse gas emissions totaled 760,268 tons of carbon dioxide-equivalent
(CO2e), a decrease of 8.25 percent over the revised 2004 baseline (Figure 2, Table 2). The majority of emissions
are carbon dioxide (95.7 percent) with the remaining 4.3 percent of emissions from methane and nitrous oxide
(Figure 3). The total includes greenhouse gas emissions from the three major sectors — Buildings, Transportation,
and Other Sources. Calculations, methods, sources, and detailed results are included in the folio of worksheets
in Appendix C.
Figure 2. Aspen emissions 2004 versus 2007
Table 2. GHG emissions 2004 versus 2007
10,000
20,000
30,000
40,000
50,000
60,000
70,000
Tons CO2e
Passenger
Cars
(Sedans,
Cabriolets)
Small SUVs
and
Small Trucks
Mediu
SU
Large
Tr
TOTAL GREENHOUSE GAS EMISSIONS
Tons CO2e
AIR TRAVEL AND AVIATION EMISSIONS
ELECTRICITY CONSUMPTION
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
2004
2007
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
20072004
GA: Air
Ambulance
GA:
Piston
GA:
Turboprops
GA: JetsAir Travel
via Other
Airports
Air Travel
via Aspen
26.8%
14.0%
828,648
760,268
Air Travel
Buildings
Commuting
HIGHWAY 8
GR
Gallons
of Fuel
14,000,000
12,000,000
10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
Around
Town
Commuting
ASPEN’S MAJOR AI
140,000
Tons CO2e/yr
Electricity
20.6%
1998 20020001999
500,000
400,000
300,000
200,000
100,000
40,000
Source 2004 (tons CO2 ) 2007 (tons CO2 ) Change
Buildings -4.0%
Electricity 166,557 156,392 -6.1%
Natural gas & propane 106,768 106,084 -0.6%
Transportation -11.6%
Ground transportation 211,175 203,471 3.6%
Air travel: commercial 186,631 147,370 -21.0%
Air travel: general aviation 145,616 129,537 -11.0%
Other
Landfill & nitrous oxide 11,902 17,414 46.3%
Total 828,648 760,268 -8.3%
Greenhouse Gas Emissions Sources: 2004 vs. 2007
e e
Note: 2004 General Aviation emissions revised from 157,856 to 145,616 tons CO2e and Aspen’s total
emissions from 840,888 to 828,648 tons CO2e.

31
One-third of the emissions are direct and indirect emissions from fuels used to heat and power buildings —
primarily that of electricity and natural gas, with less than 1 percent coming from propane. Nearly two-thirds
of the emissions are from the Transportation sector, including commercial and private air travel, personal and
commercial vehicles, public transit, school buses, local government vehicles, and miscellaneous fuel uses
(Figure 4). These ratios are consistent with those of the 2004 baseline inventory. Of the subcategories — electricity,
natural gas & propane, ground transportation, aviation, landﬁll, and nitrous oxide sources — commercial air
travel and general aviation contribute the most to Aspen’s emissions (36.4 percent), reﬂecting the town’s main
economic driver — tourism (Figure 5).
From 2004 to 2007, Aspen’s total energy use dropped 5.5 percent, largely a result of the decrease in fuel consumption
in the Transportation sector. Consumption of electricity and natural gas increased from the 2004 baseline (Table 3).
Figure 3. Emissions by greenhouse gas 2004 versus 2007
Carbon Dioxide Methane Nitrous Oxides
EMISSIONS BY GREENHOUSE GAS
Commercial Air Travel
147,370 tons
Tons CO2e
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
SUMMARY OF CONSUMPTION: BUILDINGS & TRANSPORTATION (2007 VERSUS 2004)
SOURCE 2004 2007 CHANGE
BUILDINGS
Electricity (kWh) 204,156,468 224,129,984 9.8%
Natural gas (Mcf) 1,815,930 1,883,692 3.7%
Propane (gal) 500,274 375,191 -25.0%
TRANSPORTATION
Ground transportation (gal) 21,259,230 20,514,406 -3.5%
Air travel & aviation (gal) 31,516,080 26,277,176 -16.6%
Table 3. Consumption: Buildings and Transportation 2004 versus 2007

32
Figure 4. Major sources 2007
t
avel
spen
Carbon Dioxide Methane Nitrous Oxide
EMISSIONS BY GREENHOUSE GAS
ASPEN EMISSIONS: MAJOR SOURCES, 2007
Tons CO2
e
Electricity Natural Gas Propane Ground
Transportation
Aviation
$10,000,000
General Aviation
129,537 tons
Commercial Air Travel
147,370 tons
All Ground
Transportation
203,471 tons
Natural Gas and
Propane
106,070 tons
Electricity
156,392 tons
Landfill and N2
O
17,414 tons
Tons CO2e
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
Figure 5. Major sources 2004 versus 2007, subcategories
ELECTRICITY CONSUMPTION
MAJOR EMISSIONS SOURCES
MAJOR GROUND TRANSPORTATION EMISSIONS
Tons CO2e
Tons CO2e
kWh
180,000
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
140,000
120,000
100,000
80,000
Aspen Electric Holy Cross
180,000,000
160,000,000
140,000,000
120,000,000
100,000,000
80,000,000
60,000,000
40,000,000
20,000,000
2004
2007
2004
2007
2004
2007
GA: Air
Ambulance
GA:
Piston
GA:
Turboprops
GA: JetsAir Travel
via Other
Airports
Air Travel
via Aspen
Landfill
Methane
GA: JetsAir Travel
via Other
Airports
Air Travel
via Aspen
Tourist
Driving
Around
Town
CommutingNatural
Gas
Electricity
Around
Town
Commuting
ASPEN’S MAJOR A
140,000
120,000
100,000
80,000
60,000
40,000
20,000
Tons CO2e/yr
General
Aviation
(Jets)
Commercial
Air Travel
via Aspen
Mcf
1,600,000
1,400,000
1,200,000
1,000,000
800,000
600,000
400,000
200,000
SourceGas
NAT
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
-
40,000
20,000
00,000
80,000
60,000
40,000
20,000
-

33
ECONOMICS & ASPEN’S GREENHOUSE GAS EMISSIONS
While Aspen’s total energy use dropped 5.5 percent from 2004 to 2007, total estimated energy costs increased
by about 38 percent – from $128 million in 2004 to $177 million in 2007.34
From 2004 to 2007, per unit costs of energy for all commodities increased (with the exception of Holy Cross
Energy, which maintained its per-kilowatt-hour rate from 2004 to 2007). Gasoline, diesel, and jet fuel prices all
increased by more than 50 percent; natural gas, propane, and electricity costs increased 20 to 40 percent per
unit energy.
Of the estimated total energy-related expenditures, ground transportation costs (up 59 percent from 2004) and
aviation fuel costs (up 42 percent) increased the most. Total electricity costs (up 19 percent) and natural gas
costs (up 26 percent) also rose signiﬁcantly (Figure 6).
As energy costs rise, energy efﬁciency and more mindful consumption will become increasingly important not
only to the environment, but to Aspen’s economy as well.
34 This is only a rough estimate by CMS based on local fuel and energy costs as well as national costs of jet fuel in 2004 and 2007. See
“Compare 2004 & 2007” in Appendix C.
Figure 6. Total cost of energy 2004 versus 2007
2004
2007
Semis
0.7%
Buses (RFTA)
1.3%
Motorcycles *0.5
0.6%
2004
2007
ASPEN BUILDING EMISSIONS, 2007
Off-Road
Fuel
Co
el
as
TION EMISSIONS
COST OF ENERGY
d-Town
ving
Tourist
Road Travel
To/From Aspen
ASPEN EMISSIONS: MAJOR SOURCES, 2007
Tons CO2
e
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
19,298 21,214
137,094
82,350
2,506
2004
2007
Electricity Natural Gas Propane Ground
Transportation
Aviation
$90,000,000
$80,000,000
$70,000,000
$60,000,000
$50,000,000
$40,000,000
$30,000,000
$20,000,000
$10,000,000
General Aviation
129,537 tons
All Ground
Transportation
Natural Gas and
Propane
106,070 tons
Electricity
156,392 tons
Landfill and N2
O
17,414 tons
$9
$8
$7
$6
$5
$4
$3
$2

34
IN PERSPECTIVE: ASPEN’S GREENHOUSE GAS EMISSIONS
Aspen accounts for approximately 0.01 percent of total U.S. emissions.35
The drop in emissions from 2004 to 2007 — 68,381 tons CO2e — is equivalent to eliminating the
emissions from 2,680 average Aspen homes.36
The emissions rate — if converted into equivalent energy content of gasoline — equals the arrival of
a very large (9,500 gallon) tanker truck every hour, night and day, all year long.37
Aspen’s annual emissions “weigh” 48 times as much
as the 16,000-ton Maroon Creek Bridge.38
That is,
Aspen emits the bridge’s weight in greenhouse gases
every 7.6 days.
If Aspen’s total energy appetite were supplied by
coal, it would require eleven 120-ton railroad cars
of coal every day. If a year’s worth of equivalent coal
consumption were piled onto 2.6-acre Wagner Park,
it would reach a depth of 155 feet (approximately a
15-story building), or enough to cover Aspen’s 43-
acre commercial core with nine feet of coal.
35 In 2007, the United States emitted 8,027 million tons CO2e, compared to Aspen’s 0.760 million tons CO2e in 2007. EIA (2008)
Emissions of Greenhouse Gases in the United States in 2007, U.S. Department of Energy. Aspen also consumed 0.0098 percent of the
nation’s energy in 2007: Aspen’s 10.08 trillion (1012) Btu / U.S. 102.4 quadrillion (1015) Btu = 0.00010. EIA (2007), Annual Energy
Outlook 2007 with Projections to 2030. U.S. Department of Energy.
36 The average Aspen home emits 25.51 tons of CO2e per year. From 2004 to 2007, emissions attributable to Aspen decreased by
68,380 tons CO2e (from 828,648 to 760,268 tons CO2e).
37 80.6 million gallons of gasoline equivalent/yr = 2.6 gallons/second = 23 very large (9,500-gallon) gasoline tankers per day, or one
tanker every 58 minutes. Similarly, the city’s annual energy consumption of gasoline equivalent would cover Aspen’s 43-acre commercial
core to a depth of 5.7 feet.
38 Maroon Creek Bridge: Concrete 30,213,000 lb; reinforcing steel 1,339,085 lb; pre-stressing steel 262,717 lb. Total 31,814,802 lb, or
15,907 tons. Aspen’s 2007 emissions: 760,268 tons CO2e, or 47.8 times Maroon Creek Bridge’s mass, soaking wet. Data from Colorado
Dept. of Transportation, personal communication, 19Sep05.

35
BUILDINGS: ELECTRICITY, NATURAL GAS, & PROPANE
Buildings and facilities account for 34.5 percent of Aspen’s total emissions.39
In 2007, commercial and residential
buildings consumed 4.6 percent more energy than in 2004. Yet, emissions from the Buildings sector decreased
by 4.0 percent over 2004 levels — largely because of the dramatically reduced carbon content of the City of
Aspen Electric portfolio, which reduced emissions by 20,458 tons CO2e — a decline equivalent to 802 Aspen
homes. The drop in emissions occurred despite the 2.9 percent increase in electricity consumption associated
with the utility. Holy Cross Energy, which comprises roughly 71 percent of total electric consumption (Figure
11), saw a 12.8 percent growth in demand from 2004 to 2007. Of Aspen’s total emissions, electric emissions
represent 20.6 percent; natural gas emissions represent 13.6 percent; and propane emissions represent 0.3
percent (Figure 7, 8).
In 2007, both electric and natural gas consumption increased over the 2004 baseline. Electric consumption rose
signiﬁcantly (up 9.8 percent) (Figure 9), and natural gas consumption increased by 3.7 percent (Figure 12).
Propane consumption decreased by 25 percent from 2004, likely a result of better data availability between 2004
and 2007.40
Propane use, however, contributes very little to Aspen’s total emissions, at just 0.3 percent.
39 “Buildings and facilities” includes energy used in street lighting, ski lifts, heated driveways, irrigation and well pumps, airport runway
lighting, snow-making equipment, wastewater treatment, ice-rink chillers, propane grills, and miscellaneous uses.
40 In 2004, Ferrellgas did not provide propane consumption data and, thus, it was assumed equal to that of Aspen’s other propane
supplier, AmeriGas. In 2007, Ferrellgas provided data. Propane consumption associated with Ferrellgas dropped by 85.51 percent, down
nearly 214,000 gallons from 2004.
mis,
mbo
cks
Motor-
cycles
2004
2007
VEHICLE TYPE SURVEY
August 2008
Medium & Heavy
Trucks/SUVs
39.1%
Large 2-Axle Trucks
2.6%
Large 3-Axle Trucks
2.4%
Semis
0.7%
Buses (RFTA)
1.3%
Motorcycles *0.5
0.6%
Passenger Cars
26.8%
Light Trucks and SUVs
26.5%
2004
2007
S
2004
2007
ASPEN BUILDING EMISSIONS, 2007
Off-Road
Fuel
ON EMISSIONS
COST OF ENERGY
Town
ng
Tourist
Road Travel
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
19,298 21,214
137,094
82,350
2,506
$90,000,000
$80,000,000
$70,000,000
$60,000,000
$50,000,000
$40,000,000
$30,000,000
$20,000,000
$10,000,000
2
2
lbs CO2e/kWh
delivered
Passenger Cars
26.8%
$9
$8
$7
$6
$5
$4
$3
$2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Figure 7. Buildings emissions 2007

36
Electric, natural gas, and propane consumption in residential buildings contributed 50.6 percent to emissions
from the Buildings sector — 16.7 percent of Aspen’s total; electric and natural gas consumption in commercial
and municipal buildings contributed 45.2 percent of building emissions — 14.9 percent of Aspen’s total
(Figure 9).
Scope: Building classification. Electricity, natural gas, and propane consumption are broken into three
categories: Residential, Commercial/Institutional, and Municipal. Commercial/Institutional includes
commercial and institutional facilities and buildings (e.g., Aspen School District and Aspen Valley
Hospital), state, and federal customers. All propane sales were assumed to be residential. Electric
demand for street lighting, public exterior lighting, traffic lights, and pumps also are included (primarily
in “commercial”). Energy used for residential, commercial, and municipal snowmelt systems is included
as well. Street lighting is included in Municipal. Electricity to drive large motors for ski lifts (Aspen
Mountain, Highlands, and Buttermilk ski areas are within the inventory boundary) is classified as
Commercial/Institutional.
Figure 8. Electricity, natural gas, propane emissions 2004 versus 2007
10,000
20,000
30,000
40,000
50,000
60,000
70,000
Tons CO2eTOTAL GREENHOUSE GAS EMISSIONS
Tons CO2e
Tons CO2e
ELECTRICITY, NATURAL GAS, AND PROPANE EMISSIONS
MAJOR SOURCES OF EMISSIONS
2007
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
2004
2007
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
Air Travel & Aviation
36.4%
26.8%
14.0%
9.1%
Aspen Electric:
Residential
1.8%
Aspen Electric:
Municipal A
10
20
30
40
50
60
70
80
90
20,000 40,000
ThousandsofTonsCO2e
828,648
760,268
Other Sources
Air Travel
Buildings
Commuting
Tons CO2e/yr
HIGHWAY
ELECTRICITY EMISS
Electricity
20.6%
Landfill
2.2% Nitrous Oxide
0.05%
1998 2020001999
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
ASPEN’S QUICKT

37
Electricity
Electric emissions in 2007 account for 59.6 percent of the emissions from the Buildings sector. In 2007, Aspen
consumed 224 million kilowatt hours of electricity, a 9.8 percent increase from 2004 (204 million kilowatt hours)
(Figure 9). Despite the signiﬁcant rise in consumption, electricity emissions decreased to 156,400 tons CO2e, 6.1
percent below the 2004 baseline emissions of 166,600 tons CO2e (Figure 11).
Figure 9. Electricity emissions and consumption, 2007. The area of each circle represents the
carbon footprint of each utility’s end-use sector.
60,000
70,000
Tons CO2e
S
ane Vendors
2004
2007
9.1%
Aspen Electric:
Residential
1.8%
Aspen Electric:
Municipal
15.0%
Aspen Electric:
Commercial
40.4%
Holy Cross:
Residential
31.4%
Holy Cross:
Commercial
10
20
30
40
50
60
70
80
90
20,000 40,000 80,000 100,000 120,000
ThousandsofTonsCO2e
Megawatt Hours
60,000
Other Sources
Air Travel
Buildings
Commuting
2007
2007
2008
2008
2004
2004
Tons CO2e/yr
AIR TR
G
A
Commercial Air Tra
via Regional Airpo
41,689 tons
Commercial Air Tra
via Aspen County Ai
105,681 tons
ASPEN EMISSIONS
2008
2008
ASPEN EMISSIONS
Off-Road: SkiCo, Yard Widgets,
Construction Equipment
3,339 tons RF
4
Commuting, Hwy 82
117,242 tons
2004
2007
HIGHWAY 82 AND COMMUTING EMISSIONS
ELECTRICITY EMISSIONS BY COMPANY AND SECTOR, 2007
y
ous Oxide
0.05%
1998 2006200520032002200120001999
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
ASPEN’S QUICKTRACKER SOURCES AND TOTAL EMISSIONS
1998 to 2008
Commercial Air Tra
via Aspen County Ai
105,681 tons
Figure 10. Electricity emissions factors, 2004 versus 2007
Aspen Total EmissionsAir Travel
Buildings
Commuting
Tons CO2e/yr
:
t
n
ge 2-Axle Trucks
2.6%
Axle Trucks
2.4%
1998 20302026
Aspen’s 2020 Target:
580,054 tons CO2e
20182014201020062002 20342022 20462042 20502038
Aspen’s 2050 Target:
165,730 tons CO2e
ELECTRICITY EMISSION FACTORS
1.26
1.79
1.72
0.60
2004
2007
lbs CO2e/kWh
delivered
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
ASPEN’S TOTAL EMISSIONS
1998 to 2050
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2

38
The decline in electric emissions relative to the increase in consumption can be explained by the significant
increase in City of Aspen Electric renewable-energy fuel mix. Aspen Electric increased its renewable-energy
portfolio considerably, from 35.7 percent renewable in 2004 to 65.8 percent in 2007. Adding in nuclear
generation via MEAN (Municipal Energy Agency of Nebraska), which provided 26.8 million of Aspen Electric’s
total supply of 69.3 million kilowatt hours in 2007, bumps the non-carbon fraction up to 72.7 percent.41
The non-
carbon generation mix resulted in a 52.8 percent drop in the utility’s carbon factor (Box 3).42
Electricity demand
from the City utility rose by 1.8 million kilowatt hours (2.9 percent) between 2004 and 2007. Despite the rise in
demand, Aspen Electric’s lower carbon content caused a decrease in emissions of 22,053 tons CO2e (Figure 10).
Holy Cross Energy’s carbon factor decreased slightly from 2004 to 2007. Electric demand for the regional
utility rose by 12.8 percent from 2004 to 2007 (an increase of 18.2 million kilowatt hours), while emissions
increased by 8.1 percent. Holy Cross’s carbon factor decreased from 1.79 lbs CO2e/kWh to 1.72 lbs CO2e/kWh
(Figure 10).
41 Renewable-energy sources include hydropower and wind. Non-carbon sources include nuclear, hydropower, and wind. Aspen Electric
generates its own hydropower and buys power from Municipal Energy Agency of Nebraska, of which the generation portfolio includes
18 percent nuclear power.
42 Carbon factors are used to calculate the amount of CO2e produced per unit of energy consumption. For example, consuming 1
kilowatt-hour of electricity supplied by Aspen Electric emits 0.60 pounds of CO2e, whereas consuming 1 kilowatt-hour of electricity
supplied by Holy Cross Energy emits 1.72 pounds of CO2e. Transmission and distribution losses are factored into the carbon factor per
delivered kilowatt hour of electricity as is fugitive methane for that portion of the fuel mix derived from coal. This methodology is applied to
both Aspen Electric and Holy Cross Energy carbon factors.
2004
2007
Mcf
1,600,000
1,400,000
1,200,000
1,000,000
800,000
600,000
400,000
200,000
AM GasSourceGas
Aspen Electric Carbon DioxideHoly Cross
ELECTRICITY EMISSIONS
NATURAL GAS CONSUMPTION
EMISSIONS
Comp
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
2004
2007
General Aviation
129,537 tons
Com
Electricity
156,392 tons
Landfill and N2
O
17,414 tons
Tons CO2e
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
Figure 11. Electricity emissions by provider 2004 versus 2007

39
Emissions calculation: Electric carbon factors. Electricity used in town emits greenhouse gases
elsewhere, including carbon dioxide emissions from the smokestacks of coal- and natural gas-ﬁred
power plants located in Northern Colorado and the Upper Great Plains. Also included are methane
emissions from the coal mines and natural gas production and distribution supplying coal- and gas-ﬁred
power plants.43
These emissions are included in the 2007 inventory, as they were in the 2004 baseline.
Electricity transmission and distribution losses also are included in the inventory and are estimated at
about 6 percent.
Aspen Electric’s service area within the Emissions Inventory Boundary is much smaller than that of Holy Cross
Energy. In 2007, Holy Cross provided 71.1 percent of the electric demand in the Aspen area, whereas Aspen
Electric provided 28.9 percent of the electricity to the area (a difference of 94.7 million kilowatt hours) (Figure
12). As a result, Holy Cross’s energy portfolio has a much greater impact on Aspen’s emissions than that of Aspen
Electric (Figures 9, 10 and 11).
43 86 percent of associated methane emissions is tied to the production, processing, and transportation of natural gas and is not a
measure of SourceGas’s direct methane emissions but rather Aspen’s proportion of the natural gas industry as a whole. Nationally, the
leakage rate is 0.57 percent. 14 percent of the methane is from the coal mining regions that supply coal to the power plants generating
electricity for Aspen’s customers. Mines in these regions emit 14 to 77 cubic feet of methane per ton of coal mined. See the worksheets in
Appendix C for details.
Figure 12. Aspen Electric service territory map. Map by Bridgette Kelly, Aspen/Pitkin County GIS.

40
Residential. Of the building types, residential buildings had the largest increase in electric consumption, up
14.4 percent. Residential buildings consumed 113 million kilowatt hours of electricity in 2007, up from 99 million
kilowatt hours in 2004. Residential buildings accounted for 50.5 percent of Aspen’s electric demand in 2007. In
line with significant increase in consumption, emissions attributed to residential buildings dropped 1.9 percent
compared to 2004 (Figure 9).
Commercial, institutional, & municipal. Commercial/Institutional and Municipal (CI&M) buildings experienced
the smallest increase in demand (up 5.5 percent) while emissions were down 17.3 percent from 2004. CI&M
buildings consumed 111 million kilowatt hours of electricity in 2007, up from 105 million kilowatt hours in 2004.
In 2007, CI&M buildings represented 49.4 percent of Aspen’s electric demand.44
Street lighting is included in
CI&M, as is electricity for large facilities such as ski lifts and the Aspen sanitation plant (Figure 9).45
Irrigation pumps. Of the total electric consumption, irrigation pumps consumed 91,600 kilowatt hours of
electricity, a decrease of 15.1 percent over 2004’s total of 108,000 kilowatt hours.46
In 2007, irrigation pumps
represented 0.04 percent of the electric demand (Figure 9).
44 Of total CI&M electricity demand, municipal uses accounted for 8.9 million kWh in 2004 and 4.2 million kWh in 2007. However, Holy
Cross did not disaggregate municipal demand in 2007 (it did in 2004: 4.6 million kWh), which makes a comparison impossible.
45 CMS does not have detailed end-use consumption data on these uses. The Aspen Skiing Company used 19.2 million kWh in
2006/2007 for its on-mountain lifts, facilities, and restaurants — including Snowmass, which is outside our inventory boundary.
46 Irrigation pumps were not classified as a separate category by Holy Cross Energy in 2004 as they were for 2007. For the 2007
inventory, both electric utilities classified irrigation pumps in their own category. This category does not include water pumping energy
(e.g., pumping water up Red Mountain well pumps, snowmaking pressure pumps).
Box 3. Aspen Electric
From 2004 to 2007, City of Aspen Electric
increased its noncarbon energy portfolio
significantly – from 44 to 73 percent
noncarbon (36 to 66 percent renewable).
In 2007, the municipal utility’s energy
portfolio included 45,589,547 kilowatt
hours of renewable energy (50,405,547
kilowatt hours noncarbon).
The city-owned utility has plans to become
100 percent renewable. Current renewable
projects for the City’s utility include build-
ing the Castle Creek hydroelectric plant,
adding 45 kilowatts of solar photovoltaics
to help power the water plant, and using
geothermal energy to develop a heating and
cooling district for the downtown core.
By nearly doubling its renewable-portfolio
from 2004 to 2007, the municipal electric
utility significantly decreased the amount
of carbon emissions per kilowatt hour of
electricity consumed. As a result, Aspen
Electric played a major role in the emissions
decrease between 2004 and 2007.
ASPEN ELECTRIC INCREASES
RENEWABLE-ENERGY PORTFOLIO

41
Natural Gas
Natural gas emissions in 2007 represented 39.5 percent of the emissions from the Buildings sector, and 13.6
percent of Aspen’s total emissions. In 2007, Aspen consumed 1.88 billion cubic feet (Bcf) of natural gas, 3.7
percent more than in 2004 (Figure 13). Emissions attributed to natural gas increased modestly from 2004 to
2007, a difference of 135 tons CO2e.
Commercial/Institutional and Municipal categories contributed roughly equally to the total emissions from natural
gas (50.8 percent residential and 49.2 percent Commercial/Institutional and Municipal).
While changes in weather are not included in the inventory, weather affects energy consumption. From 2004
to 2007, the number of heating degree days decreased by 4.8 percent, representing a decrease in heating
requirements in 2007. Despite the decrease, natural gas consumption increased over the period.
Propane
Propane emissions in 2007 represented 0.95 percent of the emissions from the Buildings sector, and 0.33
percent of Aspen’s total emissions. In 2007, Aspen consumed 375,200 gallons of propane, 25 percent less than
in 2004 (500,300 gallons).
The large difference in consumption is likely the result of changes in data availability. Ferrellgas did not provide
propane consumption data in 2004, and it was assumed equal to that of Aspen’s other main propane supplier,
AmeriGas. In 2007, Ferrellgas agreed to provide data. This reporting decreased total propane consumption and
emissions by 24.6 percent. Propane use, however, contributes very little to emissions from the Buildings sector
as well as to Aspen’s total emissions. Emissions attributed to propane decreased a corresponding amount from
2004 to 2007, down 819 tons CO2e.
Propane emissions are chieﬂy from residential buildings, either for space or water heating. Propane cylinders for
construction jobs during winter are also counted.
Figure 13. Natural gas consumption 2004 versus 2007
2004
2007
2004
2007
2004
2007
Landfill
Methane
s
140,000
120,000
100,000
80,000
60,000
40,000
20,000
General
Aviation
(Jets)
Commercial
Air Travel
via Aspen
Commercial
Air Travel
via Other
Airports
Commuting
via Hwy 82
Around-Town
Driving
Tourist
Road Travel
To/From Aspen
Mcf
1,600,000
1,400,000
1,200,000
1,000,000
800,000
600,000
400,000
200,000
AM GasSourceGas
Aspen Electric Carbon DioxideHoly Cross
EM
ASPEN E
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
2004
2007
Electricity Natura
$90,000,000
$80,000,000
$70,000,000
$60,000,000
$50,000,000
$40,000,000
$30,000,000
$20,000,000
$10,000,000
General Aviation
129,537 tons
Electricity
156,392 tons
Landfill and N2
O
17,414 tons
Tons CO2e
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
-
40,000
20,000
00,000
80,000
60,000
40,000
20,000
$9
$8
$7
$6
$5
$4
$3
$2
-

42
TRANSPORTATION
The Transportation sector comprises 63.2 percent of Aspen’s total emissions, emitting 480,378 tons CO2e
through the combustion of 46.8 million gallons of gasoline, diesel, and jet fuel. This is a decrease of 11.7 percent
compared to 2004 (Figure 15).
Figure 14. Transportation emissions
Figure 15. Ground transportation emissions 2004 versus 2007
2004
2007
2004
2007
6,000,000
4,000,000
2,000,000
Off-Road
Fuel
SkiCo
Diesel
& Gas
RFTATourist
Driving
Around
Town
Commuting
ASPEN’S MAJOR AIR AND GROUND TRANSPORTATION EMISSIONS
2007 COS
Compa
140,000
120,000
100,000
80,000
60,000
40,000
20,000
Tons CO2e/yr
General
Aviation
(Jets)
Commercial
Air Travel
via Aspen
Commercial
Air Travel
via Other
Airports
Commuting
via Hwy 82
Around-Town
Driving
Tourist
Road Travel
To/From Aspen
Mcf
1,600,000
1,400,000
1,200,000
1,000,000
800,000
600,000
400,000
200,000
AM GasSourceGas
EMISSIONS
Comp
ASPEN EMISSION
Tons CO2e
160,000
140,000
80,000
60,000
40,000
20,000
19,298
2004
2007
Electricity Natural Gas
$90,000,000
$80,000,000
$70,000,000
$60,000,000
$50,000,000
$40,000,000
$30,000,000
$20,000,000
$10,000,000
General Aviation
129,537 tons
Com
Electricity
156,392 tons
Landfill and N2
O
17,414 tons
Tons CO2e
900,000
800,000
700,000
-
40,000
20,000
00,000
80,000
60,000
40,000
20,000
$9
$8
$7
$6
$5
$4
$3
$2
-
10,000
20,000
30,000
40,000
50,000
60,000
70,000
Tons CO2e
Passenger
Cars
(Sedans,
Cabriolets)
Small SUVs
and
Small Trucks
Medium/Large
SUVs &
Large “Light”
Trucks
2-Axle
Medium Duty
Trucks & RVs
3-Axle Trucks,
Dump Trucks
Semis,
Combo
Trucks
Motor-
cycles
e
Buildings
Commuting
2007 20082004 2008
Off-Road: SkiCo, Yard Widgets,
Construction Equipment
3,339 tons RFTA Buses
4,395 tons
Commuting, Hwy 82
117,242 tons
VEHIC
Motorcycles *0.5
0.6%
Passenger Cars
26.8%
Light Trucks and SUVs
26.5%
2004
2007
HIGHWAY 82 AND COMMUTING EMISSIONS
2004
2007
GROUND TRANSPORTATION
ASPEN BUI
Gallons
of Fuel
14,000,000
12,000,000
10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
Off-Road
Fuel
SkiCo
Diesel
& Gas
RFTATourist
Driving
Around
Town
Commuting
ASPEN’S MAJOR AIR AND GROUND TRANSPORTATION EMISSIONS
2007 CO
Com
140,000
120,000
Tons CO2e/yr
Tons CO2e
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
19,298
137,094
$90,000,000
1998 2006200520032002200120001999
400,000
300,000
200,000
100,000
Passenger Cars
26.8%
40,000
20,000
$9

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