Bozeman GHG Emission Report

City of Bozeman

2020 Community

Greenhouse Gas

Emissions Inventory

Report

Prepared by

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Table of Contents

Executive Summary ES-1

Introduction 1

An Overview of 2020 Emissions 5

Year-Over-Year Comparison21

Carbon Sequestration32

Summary37

Appendix A: Data Sources38

Appendix B: Emissions Factors40

Table of Tables

Table 1. Annual greenhouse gas emission intensities in Bozeman, the US, and globally. .....................................................7

Table 2. Bozeman’s 2020 greenhouse gas emissions by sector and source. ..........................................................................19

Table 3. Detailed contributing factors to GHG emissions increases and decreases between 2018 and 2020. ..............30

Table 4. Annual carbon flux within the Bozeman city boundary. ...................................................................................................35

Table 5. Emissions data sources and if they were calculated or estimated in this report. .....................................................38

Table 6. Summary of greenhouse gas emissions factors. ...............................................................................................................40

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Table of Figures

Figure ES 1. 2020 greenhouse gas emissions by sector.........................................................................................................................................

Figure ES 2. Total GHG emissions between 2008-2020 and the City of Bozeman’s 2025 emissions reduction goal (mt CO 2

e). .....

Figure ES 3. Annual per capita greenhouse gas emissions and population growth from 2008-2020. .....................................................

Figure ES 4. US greenhouse gas emissions over time (via New York Times). ..................................................................................................

Figure ES 5. Progress towards the 2020 Bozeman Climate Plan goals.. ...........................................................................................................

ES-1

ES-2

ES-3

ES-4

ES-5

Figure 1. Bozeman City Limits......................................................................................................................................................................................... 3

Figure 2. 2020 greenhouse gas emissions by scope.............................................................................................................................................. 6

Figure 3. Bozeman’s 2020 stationary energy use sector greenhouse gas emissions. .................................................................................. 10

Figure 4. Bozeman’s 2020 transportation sector greenhouse gas emissions. ................................................................................................. 12

Figure 5. Bozeman's 2020 waste sector greenhouse gas emissions. ................................................................................................................ 14

Figure 6. Bozeman’s 2020 greenhouse gas emissions by sector and source. ................................................................................................ 18

Figure 7. Changes in GHG emissions between inventories................................................................................................................................... 22

Figure 8. Progress towards the 2020 Bozeman Climate Plan goals. .................................................................................................................. 23

Figure 9. Year-over-year greenhouse gas emissions by sector (2008-2020)................................................................................................... 25

Figure 10. Year-over-year per capita greenhouse gas emissions and population (2008-2020). ................................................................. 26

Figure 11. Population increases between 2010-2020 in select Montana cities and unincorporated areas. .............................................. 27

Figure 12. Contributing factors to GHG emissions increases and decreases between the 2018 and 2020 inventories. ..................... 29

Figure 13. National trends in greenhouse gas emissions between 2005-2021. ............................................................................................... 31

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Executive Summary

The natural surroundings of Bozeman are integral to

the community’s quality of life and economy; the clean

environment benefits residents and visitors alike. While

climate disruption continues to impact southwest Montana’s

ecosystems, water resources, public health, agriculture, and

tourist economy, the City of Bozeman’s 2020 Climate Plan

offers a path forward to ensure a more vibrant future for

all residents. Bozeman has set a community-wide goal of

reaching carbon neutrality by 2050, and the pathway to this

goal includes reducing greenhouse gas (GHG) emissions

26% below 2008 levels by 2025 and transitioning to

100% net clean electricity by 2030. Bozeman measures

greenhouse gas emissions bi-annually to monitor progress

towards these goals and to better understand effective

interventions. The following report summarizes the City of

Bozeman’s greenhouse gas emissions in 2020, including

an analysis of emission sources, trends, and an estimate of

terrestrial carbon sequestration.

Figure ES 1. 2020 greenhouse gas emissions by sector.

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Bozeman developed a 2020 greenhouse gas emissions inventory to track progress toward

reduction goals. Bozeman’s 2020 GHG emissions totaled 548,746 metric tons of carbon dioxide

equivalent (mt CO 2

e) inclusive of all GHG emissions generated in Bozeman from building energy

use, transportation, and waste.

In 2020, building energy emissions were the largest

contributor to Bozeman’s GHG emissions, comprising

58% of total emissions. Transportation emissions

comprised 32% of total emissions, waste emissions

comprised 10%, and refrigerant leakage emissions

comprised 0.2%. See Figure ES 1. National trends follow

a similar pattern with building energy representing the

largest emissions sector followed by the transportation

sector.

Bozeman’s total emissions have increased 5% from

the baseline year of 2008. See Figure ES 2. A key

contributing factor to the overall increase in emissions

since 2008 is population growth within the City of

Bozeman and surrounding areas. Bozeman’s per

capita emissions have decreased 30% from 2008 while

population has increased 50%. See Figure ES 3.

Figure ES 2. Total greenhouse gas emissions between 2008-2020 and

the City of Bozeman’s 2025 emissions reduction goal (mt CO 2

e).

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Figure ES 3. Annual per capita greenhouse gas emissions and population growth from 2008-2020.

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Total emissions in Bozeman decreased by 10% in 2020 from the recent inventory in 2018. See Figure ES2. Changes

between 2018 and 2020 reflect similar shifts in emissions patterns across the country. As shown in Figure ES 4,

trends in US emissions decreased between 2018 to 2020 in the transportation, electricity, and buildings sectors.

These decreases are believed to be strongly influenced by the COVID-19 pandemic.

The 2020 GHG inventory reflects the City’s advancement toward its 2020 Bozeman Climate Plan goals. However,

continuous action is needed to meet the City’s goals and secure a more sustainable future (Figure ES 5).

Figure ES 4. US greenhouse gas emissions over time (via New York Times).

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Figure ES 5. Progress towards the 2020 Bozeman Climate Plan goals.

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Introduction

To help Bozeman reach its carbon neutrality goals, the

City has completed a community wide greenhouse

gas (GHG) emissions inventory to measure and identify

sources of emissions within the community.

GHG emissions are heat-trapping gases that contribute

to climate change through atmospheric warming. The

primary GHG emissions are carbon dioxide (CO2),

methane (CH4), nitrous oxide (N2O) and fluorinated

gases – hydrofluorocarbons (HFCs), perfluorocarbons

(PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride

(NF3). While carbon dioxide, methane, and nitrous

oxide come from a variety of natural sources, humanrelated

emissions of these gases are responsible

for the substantial increase that has occurred in the

atmosphere since the Industrial Revolution. Today,

global greenhouse gas emissions are higher than at

any time during the last 650,000 years. * Human-related

GHG emissions are often produced as a result of

burning fossil fuels (coal, natural gas, oil) for buildings

and transportation, industrial activity, agriculture, solid

waste decomposition, wastewater treatment, and other

activities.

Lotus Engineering and Sustainability, LLC (Lotus) was

hired to complete the 2020 calendar year community

wide GHG emissions inventory. The inventory was

developed using the standard methodology outlined

in the Global Protocol for Community-Scale GHG

Inventories (GPC) for a BASIC inventory. BASIC

inventories include emissions generated from building

energy, transportation, and waste.

Additional emission sources (sometimes referred to as

BASIC+ sources), such as electricity transmission and

distribution (T&D) losses and transboundary aviation, **

were included in the 2020 inventory. Unless otherwise

noted, all emission totals in this report include BASIC+

sources. See the subsection titled BASIC+ Emissions for

more information. This report also estimates the

* ACS Climate Science Toolkit

** Per the GPC protocol, “The transportation emissions from large regional transit hubs (e.g., airports or seaports) serving the city, but outside of the geographic

boundary, should be counted in scope 3. These emissions are driven by activities within the city and should be included to provide a more holistic

view of the city’s transportation sector.”

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average annual net carbon flux from Bozeman’s land

and forests within the city boundary. See subsection

Carbon Sequestration for more information.

The following report reviews 2020 GHG emissions

sectors and sources, and progress toward Bozeman’s

climate goals.

Inventory Boundary

Per the GPC, communities shall establish a geographic

boundary that identifies the spatial dimensions or

physical perimeter of the inventory’s boundary. The

boundary for the Bozeman inventory reflects the

physical City limits (Figure 1).

Moving forward the City has committed to publicly reporting

emissions every two years with the next inventory reflecting 2022.

Greenhouse gas inventories help the City monitor emissions trends

and recognize reduction opportunities.

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Figure 1. Bozeman City Limits.

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Note on COVID-19 Impacts

While Bozeman’s total emissions decreased from 2018

to 2020, it is important to note that 2020 is an outlier

year due to the COVID-19 pandemic. National trends

saw reduced travel, decreased commercial energy

usage, and increased waste disposal. With more

people working from home and traveling less, there

were fewer commuting and air travel emissions. As

businesses slowed and closed operations, commercial

building energy emissions decreased. Increased use

and disposal of single-use items significantly increased

waste emissions. The 2020 drop in national and local

emissions does not necessarily represent a new normal

and it is unlikely these reductions will be durable without

sustained systemic change.

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An Overview of 2020 Emissions

Emissions By Scope

Emission sources fall into one of three scope categories, which vary depending on the emissions point of release in

relation to the city boundary.

Scope 1 includes

GHG emissions from

sources within the

city boundary, such

as building fuel use

(other than electricity),

vehicle activity within

the City, and compost

deposited within city

limits.

Scope 2 includes

emissions from the

use of grid-supplied

electricity, heat, steam,

and cooling within the

city boundary.

The only scope 2 emission source

for Bozeman is grid-supplied

electricity, including electric use by

electric vehicles.

Scope 3 emissions

include all other GHG

emissions occurring

outside the city as

a result of activities

within the City

boundary.

For example, landfilled waste is a

scope 3 emission for Bozeman, as

waste generated in Bozeman is

taken to be disposed of outside the

city boundary.

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Scope 1 emissions accounted for 58% of Bozeman’s

total emissions (317,702 mt CO2e). On-road vehicle

fuel combustion, residential natural gas usage, and

commercial and industrial electricity usage were the

three largest contributors to scope 1 emissions in 2020.

Scope 2 emissions from grid-supplied electricity made

up 26% of total emissions from the City (142,096 mt

CO 2

e). Scope 3 emissions made up 16% of Bozeman’s

emissions (88,949 mt CO2e), with landfilled waste and

emissions from the Yellowstone/Bozeman International

Airport making up the majority of scope 3 emissions.

Figure 2 shows the percentage of emissions from each

scope. *

* As noted above, additional Scope 3 emission sources (sometimes

referred to as BASIC+ sources) from transmission and distribution (T&D) losses

and transboundary aviation were calculated for the 2020 inventory. See the

subsection titled BASIC+ Emissions for more information.

Figure 2. 2020 greenhouse gas emissions by scope.

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Normalized Emissions

Bozeman’s population of 53,293 in 2020, emissions per resident were approximately 10.3 mt CO2e. Bozeman per

capita emissions are lower than US average emissions per capita by approximately 30%. The lower per capita

emissions rate is driven by lower industry-related emissions compared to other cities, as well as newer and more

efficient buildings. Per capita emission intensities are shown in Table 1.

Table 1. Annual greenhouse gas emission intensities in Bozeman, the US, and globally.

Metric

2018 Annual Greenhouse Gas

Emissions (mt CO2e)

2020 Annual Greenhouse Gas

Emissions (mt CO2e)

Bozeman per capita 12.5 10.3

National per capita * 15.8 13.5

International per capita 4 4.8 4.5

* National and international annual per capita emissions data are from Statista; data are from 2018 & 2020.

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Emissions sectors are the broad categories of activities that result in GHG emissions. Bozeman’s inventory is split into

the following emissions sectors:

Stationary Energy: emissions sourced from buildings

(electricity and natural gas usage), propane and

diesel combustion, and transmission and distribution

losses (T&D).

Transportation: emissions originating from gas and

diesel vehicles, aviation, transit and electric vehicles,

and T&D losses from electric vehicles.

Solid Waste and Wastewater Treatment: emissions

released from organic material, solid waste this is

inclusive of transportation, collection, and processing

of waste.

Industrial Processes and Product Use: emissions

stemming from refrigerant leaks in building heating,

ventilation, and air conditioning (HVAC) systems.

Each sector contains individual sources, which represent the specific activities resulting in the emissions. Emissions

sectors and the sources within them are further discussed in the following subsections. A summary of emissions from

BASIC+ emissions, which captures all scope 1, 2, and 3 emissions sources, is included following the emission sector

summaries.

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Stationary Energy

Emissions from stationary energy accounted for 57 percent of Bozeman’s

total GHG emissions (315,412 mt CO2e).

The stationary energy sector includes emissions from

buildings, primarily from electricity and natural gas

usage. Other sources of stationary energy emissions

include propane and diesel combustion, as well as

T&D losses. Fugitive emissions, or emissions from the

sourcing, transport, and leakage of natural gas, are

also included.

Figure 3 breaks down the specific sources of

stationary energy emissions. Overall, electricity use,

including T&D losses, accounted for 48% (150,733 mt

CO2e) of stationary energy emissions, and natural

gas use, including fugitive emissions, made up 51%

(160,645 mt CO2e). Propane, residential wood, and

stationary diesel together accounted for the remaining

stationary energy emissions (see Table 2).

Splitting energy use by building type provides a more

detailed understanding of the sources contributing

to stationary energy emissions. In 2020, commercial

buildings (e.g., shops, offices, hotels, warehouses,

and other places of business) accounted for 56%

of Bozeman’s stationary energy emissions (175,646

mt CO2e), while homes made up 44% of stationary

energy emissions (139,765 mt CO2e). Commercial

natural gas usage was the largest source of stationary

energy emissions (91,589 mt CO2e). Commercial

building emissions decreased by 13% from 2018 while

residential building emissions decreased by 3% over

the same period. This is largely due to COVID-19

impacts and restrictions that prevented employees

from working from the office and students from

attending school and forced them to work and learn

from home instead.

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Figure 3. Bozeman’s 2020 stationary energy use sector greenhouse gas emissions.

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Transportation

The transportation sector accounted for 32 percent of Bozeman’s total GHG

emissions (177,593 mt CO2e).

Figure 4 provides a breakdown of the contributing

sources to emissions from the transportation sector.

Emissions from gasoline vehicles (including emissions

from ethanol) made up 53% of transportation emissions

(95,008 mt CO2e) and diesel vehicles made up 24%

(41,932 mt CO2e). Aviation emissions made up 23% of

transportation emissions (39,999 mt CO2e). * Together,

transit vehicles, electric vehicles, and T&D losses from

electric vehicle charging made up under one percent

of total transportation emissions. See Table 2 for more

detail. Between 2018 and 2020, transportation

emissions decreased by 23%. These reductions can

be attributed to COVID-19 impacts and restrictions that

limited travel within Bozeman and across the country.

This trend mirrors the National trend in transportation

emissions between 2018 and 2020, see Figure 13. The

high emissions stemming from gas and diesel vehicles

(77%) mirrors national trends, the data conveys an

opportunity for more sustainable travel.

* Per the GPC protocol, transboundary aviation is defined as “The transportation emissions from large regional transit hubs (e.g., airports or seaports) serving

the city, but outside of the geographic boundary, should be counted in scope 3. These emissions are driven by activities within the city and should be included to

provide a more holistic view of the city’s transportation sector.”

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Figure 4. Bozeman’s 2020 transportation sector greenhouse gas emissions.

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Waste and Wastewater

Waste and wastewater emissions made up nine percent of Bozeman’s total

2020 emissions (54,856 mt CO2e).

The solid waste generated in Bozeman is disposed

of outside the City boundary at Logan Landfill.

Some organic material is taken outside of the City

boundary for composting, while other organic material

is composted within City limits. Solid waste from

residential, commercial, and industrial sources made up

67% of total waste and wastewater emissions (36,733

mt CO2e). The closed Story Landfill comprised 26% of

total waste and wastewater emissions (14,388 mt CO2e)

where methane from historically landfilled organic

materials is captured, flared, and converted to CO2

before it is emitted into the atmosphere. Emissions from

the transport, collection, and processing of waste made

up 5% of total waste emissions (2,952 mt CO2e) and

compost made up 1% of total waste emissions (501 mt

CO2e). See Table 2. Composting organic materials, like

yard residuals and kitchen scraps, reduces emissions

compared to landfilling. Solid waste emissions

increased in 2020 from 2018 by 70% due to several

changes. The largest driver in the emissions change

was the updated global warming potential for methane,

which increased the impact of methane emissions by

6%. The global warming potential of methane is the

amount of impact that one metric ton of the greenhouse

gas methane has on global warming compared to

one metric ton of the greenhouse gas carbon dioxide.

Every metric ton of methane emitted creates the same

amount of atmospheric warming as 29.8 metric tons of

carbon dioxide. Methane is the primary greenhouse gas

emitted when solid waste decomposes. Other smaller

factors including COVID-19 impacts on the landfilling of

waste and the increase in population also contributed

to the emissions rise in 2020.

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Wastewater treatment was negligible in terms of total

emissions (0.5% of waste emissions and 280 mt CO2e,

Figure 5). All wastewater produced in Bozeman is

treated at the Bozeman Water Reclamation Facility

within the city boundaries. Wastewater treatment

emissions are mostly impacted by population, the

volume of wastewater treated, and treatment processes

at the facility.

Figure 5. Bozeman’s 2020 waste sector greenhouse gas emissions.

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Industrial Processes and Product Use

In 2020, emissions from refrigerant leaks made up 0.2% of Bozeman’s total

emissions (886 mt CO2e).

Emissions from refrigerant leaks in building HVAC

systems are the only source included in the industrial

processes and product use sector for Bozeman. These

emissions were estimated assuming that 25% of

Bozeman’s commercial square footage is refrigerated and

a standard 5% leakage rate based on IPCC refrigerant

leakage emissions methodologies. Refrigerant leaks in

building HVAC systems, beyond their emissions impact,

can have significant negative effects on human health

as harmful chemicals and substances are released with

leaks.

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BASIC+ Emissions

As noted in the introduction, BASIC+ sources from

electricity transmission and distribution (T&D) losses

and transboundary aviation were calculated for the

2020 inventory. Together these sources accounted

for 48,908 mt CO2e, approximately 9% of overall

emissions.

Transmission and Distribution

Losses

T&D losses represent electricity that is generated

but does not reach intended customers due to

inefficiencies in the transmission and distribution

systems. The T&D loss rate is estimated by the utility,

NorthWestern Energy. These losses can range yearto-year

and can be reduced through the utility making

upgrades to the grid. In 2020, it was estimated that

6.27% of electricity did not make it to the intended

customer resulting in approximately 21 million kWh lost

on the way to Bozeman. The total emissions from these

losses are 8,909 mt CO2e.

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Transboundary Aviation

Emissions from Bozeman Yellowstone International

Airport are considered transboundary aviation

emissions due to the airport being outside the City

boundary. Per the GPC protocol, “The transportation

emissions from large regional transit hubs (e.g.,

airports or seaports) serving the city, but outside of

the geographic boundary, should be counted in scope

3. These emissions are driven by activities within

the city and should be included to provide a more

holistic view of the city’s transportation sector.” * Of

the airport’s total 2020 emissions, 39,999 mt CO2e

were attributable to the City of Bozeman (7% of total

emissions). Traditionally, Bozeman has worked with

the airport to determine the proportion of the airport’s

activity that occurs as a result of Bozeman’s residents.

For this inventory, Bozeman assumes that 46.7% of

Bozeman Yellowstone International Airport emissions

are attributable to residents of the city.

* See page 72 of the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories.

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Emissions by Source

Figure 6 shows the percentage of emissions produced by each sector and source, while Table 2 displays the quantity

of emissions. Emissions from each sector are described in more detail in the previous sections. The largest sources of

Bozeman’s emissions are on-road gasoline and commercial natural gas use, each comprising 17% of total emissions.

The next largest emissions source is commercial electricity usage, comprising 14% of total emissions.

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Figure 6. Bozeman’s 2020 greenhouse gas emissions by sector and source.

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Table 2. Bozeman’s 2020 greenhouse gas emissions by sector and source.

Emissions Sources

Scope

Emissions

(mtCO2e)

Percent

Residential Fuel Use 1, 2,3 139,765 25%

Residential Electricity 2 67,369.0 12%

Residential Natural Gas 1 63,666.9 12%

Residential Propane 1 2,062.3 0.4%

Residential Wood 1 233.1 0.04%

Fugitive Emissions 1 2,209.9 0.4%

Transmission/Distribution Losses 3 4,224.0 1%

Commercial Energy 1, 2,3 175,646 32%

Commercial Electricity 2 74,470.3 13.5%

Commercial Natural Gas 1 91,588.8 17%

Commercial Propane 1 1,670.9 0.3%

Commercial Diesel 1 68.0 0.01%

Fugitive Emissions 1 3,179.0 1%

Transmission/Distribution Losses 3 4,669.3 0.5%

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Emissions Sources

Scope

Emissions

(mtCO2e)

Percent

Transportation 1, 2, 3 177,593 32%

On-Road Gasoline 1 95,007.7 17%

On-Road Diesel 1 41,932.5 8%

On-Road Electricity 2 272.4 0.05%

Transit 1 381.3 0.1%

Aviation 3 39,998.8 7%

Waste 1, 3 54,856 10%

Landfilled 3 36,733.1 7%

Compost 1,3 501.1 0.1%

Closed Landfill 1 14,388.3 3%

Waste Transport, Collection, and Processing 3 2,952.7 0.5%

Wastewater 1 280.5 0.05%

Industrial Processes and Product Use 1 886 0.2%

Refrigerant Leaks 1 886.3 0.2%

Total 548,746 100%

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Year-Over-Year Comparison

New Emissions Sources in 2020

For this iteration of the inventory, new emissions data

was available for the following sources: commercial

stationary diesel use and refrigerant use. The

methodology for estimating residential and commercial

propane was modified from previous inventories

that used national and statewide statistical data to

estimate usage. In 2020, propane consumption was

estimated based on usage estimates from one of the

primary propane providers in Bozeman. Data from

these sources was found to be reliable and replicable

and was therefore included in the 2020 inventory. See

Appendix A for specific data sources. It should be noted

that this inventory uses the most recent global warming

potentials (GWP) for methane and nitrous oxide from

the Intergovernmental Panel on Climate Change’s Sixth

Assessment Report. The methane GWP increased from

28 to 29.8 and nitrous oxide GWP increased from 265

to 273.

Year-Over-Year Emissions

Bozeman has faced the local challenge of rapid

population growth and development, along with the

national challenge of COVID-19, which influenced

emissions in 2020. Year over year comparisons help

Bozeman better understand patterns overtime to create

effective change (Figure 7). Bozeman’s total emissions

have increased 5% since the baseline year of 2008,

but the trend has fluctuated. Bozeman saw increased

emissions from 2008 to 2012, which was followed

by decreased emissions from 2012 to 2016. This was

largely due to a reduction in the carbon intensity of grid

supplied electricity and commercial building efficiency

improvements. The increase in emissions from 2016

to 2018 was largely related to population growth, and

the decrease in emissions from 2018 to 2020 was

influenced by the COVID-19 pandemic. Continued work

to reduce Bozeman’s contribution to climate change,

through City-led programs, community initiatives, and

individual actions, is needed to meet the emissions

reduction goals identified in the 2020 Bozeman Climate

Plan (Figure 8).

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Figure 7. Changes in GHG emissions between inventories. Red arrows indicate an increase in emissions from the previous inventory, while

green arrows indicate a decrease in emissions from the previous inventory.

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Figure 8. Progress towards the 2020 Bozeman Climate Plan goals.

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Year-Over-Year Emissions by Sector

Since 2008 solid waste emissions increased 69%

and transportation emissions increased 16%, primarily

due to the increased Global Warming Potential (GWP)

of methane and increase of Vehicle Miles Traveled

within the City boundary. Other sectors have been

decreasing overtime including: wastewater treatment

emissions decreased 70%, commercial and industrial

building energy usage emissions decreased 6%, and

residential building energy usage emissions decreased

18% (Figure 9). The decreasing emissions are largely

attributed to more efficient commercial buildings and

the reduced use of commercial buildings during the

COVID-19 pandemic.

Compared to the most recent inventory year of 2018,

Bozeman’s total emissions have decreased 10%.

Between these two years, solid waste emissions

increased 70%, while residential building energy

usage emissions decreased 3%, commercial and

industrial building energy usage emissions decreased

13%, wastewater treatment emissions decreased

7%, and transportation emissions decreased 23%.

The fluctuations since 2018 follow national trends of

emissions reductions due to COVID-19 in each sector.

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Figure 9. Year-over-year greenhouse gas emissions by sector (2008 to 2020).

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Per Capita Emissions

In contrast to total emissions, Bozeman’s per capita

emissions have decreased 30% from the baseline

year (Figure 10). Between 2018 and 2020, per capita

emissions have decreased 18% while Bozeman’s

population increased by 9% (48,751 to 53,293). This

means that residents are generating fewer emissions

per person in 2020 compared to 2018.

Since Bozeman’s 2008 baseline inventory year, the City

of Bozeman’s population has experienced sustained

and rapid growth. The City’s population increased

50% between 2008 and 2020 (Figure 10). During this

same period, the cities and unincorporated areas

surrounding Bozeman grew at a comparable rate or

faster. This regional growth contributes directly to traffic

and economic activity in Bozeman, which influence

emissions. Other major cities in Montana, such as

Missoula, Helena, and Whitefish, have also experienced

significant growth, but at a comparatively lower rate.

Figure 10. Year-over-year per capita greenhouse gas emissions and

population (2008-2020).

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Figure 11. Population increases between 2010-2020 in select Montana cities and unincorporated areas. *

* Montana Department of Commerce Census & Economic Information Center

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Other Drivers of Emissions Changes

While COVID-19 pandemic impacts drove a large

portion of the emissions reductions between 2018

to 2020, there were other forces at play which also

contributed to changes in emissions. Energy use

and other input data were analyzed using the ICLEI

Contribution Analysis tool for their influence on

emissions changes. Between 2018 and 2020, larger

drivers of emissions increases were the growth in

population, increase in number of jobs, increases

in waste generation, and a slightly warmer summer.

Drivers of emissions reductions between the two years

include decreased vehicle miles traveled per person,

a cleaner electric fuels mix, and a warmer winter. See

Figure 11 and Table 3. Note that several emissions

sources were not analyzed by the ICLEI Contribution

Analysis tool, such as aviation, transit, and wastewater

treatment, as these sources are more nuanced and

require a more complex analysis to determine their

impact on emissions trends.

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Figure 12. Contributing factors to GHG emissions increases and decreases between the 2018 and 2020 inventories.

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Table 3. Detailed contributing factors to GHG emissions increases and decreases between the 2018 and 2020 inventories.

Contributing Factor

Emissions Change

(mt CO2e)

Emissions Change

(mt CO2e)

50,156

Waste model difference 33,678

Growth in employment 13,199

Increased therms per

household

2,217

Refrigerants 886

Hotter summer 396

EVs 256

Fugitive Emissions 210

Stationary Diesel 68

Compost 12

Contributing Factor

Emissions Change

(mt CO2e)

Wastewater -23

Aviation -848

Residential Wood -1,082

T&D Losses -1,404

Heating fuels mix -2,064

More households using

electric heat

-2,322

Warmer winter -4,889

Decreased commercial therms

per job

Decreased on-road emissions

per mile

Decreased waste generation

per person

Decreased commercial kWh

per job

-9,491

-11,625

-13,317

-14,091

Decreased kWh per household -21,209

Electricity fuel mix -21,371

Off-road -25,178

Decreased VMT per person -28,746

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Comparison with National Trends

City of Bozeman emissions were reduced by 10% between 2018 to 2020. The building energy and transportation

sectors decreased emissions while the waste sector emissions increased. These trends mirror trends at the National

level. In the US, emissions also decreased between 2018 to 2020 and saw significant COVID-related decreases to

the transportation sector and positive impacts of the greening of the electricity grid on electricity sector emissions

(Figure 12). National data from 2021 suggests that GHG emissions will likely increase as the world recovers from the

COVID-19 pandemic.

Figure 13. National trends in greenhouse gas emissions between 2005-2021.

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Carbon Sequestration

Bozeman’s parks and urban

forests provide a myriad

of ecosystem benefits and

services. Urban forests help

filter air and water as well as

provide cooling and public

health benefits. They also

perform a vital function of

removing carbon dioxide out

of the air, which is commonly

referred to as sequestration.

Terms and Definitions

Terrestrial carbon sequestration is the process by

which atmospheric carbon dioxide is taken up by

plants through photosynthesis and stored as carbon

in biomass and soils. The plants and soil that hold the

carbon taken from the atmosphere make up a carbon

sink. The quantity of carbon stored in the plants and soil

is the carbon stock. Plants are continually taking in the

carbon from the atmosphere and storing it. But when

plants senesce, decompose, burn, or land changes

from one cover type to another (i.e., from grassland

to developments), carbon gets released back into the

atmosphere, known as the carbon cycle. Emissions are

the loss of carbon to the atmosphere (positive value)

and removals are the carbon sequestered from the

atmosphere (negative value); net carbon flux is the

sum of emissions and removals. Ecosystems provide a

natural carbon sink through trees, soils, grasslands,

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etc. Emissions from land and forests occur as part of the

natural carbon cycle, but emissions can occur following

disturbance events, such as fire, insects and diseases,

or land-use changes. Typically, in the United States,

land and forests are a net carbon sink, rather than a

source of greenhouse gas emissions. *

Methodology

To estimate Bozeman’s greenhouse gas emissions

and removals from Bozeman’s land and forests, the

ICLEI, Local Governments for Sustainability (ICLEI)

Land Emissions and Removal Navigator (LEARN)

tool was used across Bozeman city limits. The ICLEI

LEARN tool estimates the average annual emissions

and removals from forests and trees outside forests

based on geospatial and cover type data (i.e., forest

land, grassland, cropland, wetland, settlement, and

other lands). Comparing two time periods provides an

estimation of changes in both emissions and removals

of carbon, the carbon flux.

The boundary of the carbon flux analysis includes

Bozeman city limits The ICLEI LEARN tool applies

emission and removal factors for both forests and trees

outside of forests (urban tree canopy). Forest factor

sets are applied to large tracts of trees that may be

present in parks, flood plains, or other areas. Trees

outside of forest factor sets are applied to the more

sparsely spaced trees typical of residential streets. For

Bozeman, only trees outside of forest factor sets were

used, as there are no extensive forested areas within

the city limits. Default trees outside forests emission

and removal factors are provided from a benchmark

city that is selected based on geography and climate.

Casper, WY, was identified as the most similar

benchmark city, though it is comparatively drier and

warmer than Bozeman. The land cover layer sourced

data from the National Land Cover Dataset (NLCD) for

the years 2011, 2013, 2016, and 2019 are at 30-meter

resolution, and an overall accuracy of 86.6% at the

Anderson Classification System, ** Level I vegetation

classification. The tree canopy layer sourced data from

the NLCD of those same years is also at 30-meter

* Carbon Stocks, Fluxes and the Land Sector, Michgan State Univeristy (2022).

** A Land Use and Land Cover Classification System for Use with Remote Sensor Data, GEOLOGICAL SURVEY PROFESSIONAL PAPER 964 (1976).

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resolution, and the data contains percent tree canopy

estimates as a continuous variable for each pixel across

all land covers and types and are generated by the

United States Forest Service (USFS). Gain or loss of

tree canopy within the city limits is then applied to the

appropriate emissions and removal factors to determine

the carbon flux.

Results

Bozeman’s trees and forests removed over a nine-year

period on average removed -1,559 metric tons of CO2e

per year. The average emissions from Bozeman’s urban

tree canopy forested land were 21 metric tons of CO2e

per year. When carbon dioxide emissions are deducted

from removals, the balance is -1,548 metric tons of

carbon dioxide sequestered per year (Table 4).

30-meter resolution of the geospatial land cover data.

In this dataset the confidence interval range for the

net greenhouse gas balance on average ranges from

-851 metric tons of CO2e per year to -2,204 metric tons

of CO2e per year. In addition, the NLCD only contains

trees outside of forest imagery for the years 2011 and

2016, thus the analysis of 2011 to 2013 and 2013 to

2016 have the same removals, emissions, and net

balance numbers. The NLCD is expected to have 2019

trees outside of forest data soon, but was not available

for this analysis. Other ways to improve the data is to

obtain high resolution tree canopy data from a third

party, but that would still require two time periods of

identical analysis to apply the change in urban tree

canopy to the trees outside of forests emissions and

removal factors.

The LEARN tool reports uncertainty in the net

greenhouse gas balance as high as +/- 45% with a

95% confidence interval (CI) largely attributed to the

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Table 4. Annual carbon flux within the Bozeman city boundary.

City

Boundary

Average

(2011-2019)

High end

range of

+45% error

Low end

range of

-45% error

Total

Removals

(t CO2e/yr)

Total

Emissions

(t CO2e/yr)

Net GHG

Balance

(Carbon

Flux)

-1,559 21 -1,548

-2,261 30 -2,245

-857 11 -852

Based on current protocol guidance, Bozeman’s net

greenhouse gas average annual net flux of carbon

of -1,548 metric tons of CO2e per year is provided for

informational purposes and was not deducted from

Bozeman’s overall greenhouse gas emissions total of

548,746 metric tons CO2e.

Beyond carbon sequestration, this analysis does not

attempt to quantify the direct and indirect ecosystem

benefits of parks and urban forests that create a healthy

environment for residents and urban wildlife. Among

the many co-benefits, trees intercept particulate matter

and reduce air pollution, while providing shade that

can reduce the urban heat island and the cooling

load of buildings. Plants and soils also act as a filter

before water enters streams and groundwater. These

ecosystem benefits are interconnected to Bozeman’s

quality of life and economy but are not quantified within

the LEARN tool.

Despite these limitations, the annual carbon

sequestration estimates from the LEARN tool are a step

towards quantifying the carbon flux of Bozeman’s urban

natural systems over time and provide an indication of

the local carbon sequestration potential. Since climate

change impacts can lead to a decline in carbon stock

through disturbance events such as insects and disease

or high-intensity wildfire, understanding these impacts

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improves our ability to manage and protect Bozeman’s

carbon stock. Examples of land management strategies

to maintain carbon stocks may include enhancing

species diversity of the urban forest and land use

planning to minimize forest, grassland, and wetland

conversion to other land cover types.

From the LEARN tool analysis, the results provide a

preliminary estimate of Bozeman’s carbon stock. In

future years, the accuracy of the carbon stock estimate

could be improved with higher resolution data and

establishing urban forest emissions and removal factors

specific to Bozeman. Knowledge of Bozeman’s carbon

stock can help inform land management practices and

enhancements that support natural climate solutions to

reduce emissions and improve community resilience.

While annual removals may seem small, it is critical

to maintain and enhance existing urban tree canopy

whenever possible. Disturbances such as insect

infestations and removal of healthy urban trees can

create larger “pulses” of emissions. Trees remain an

essential tool in conserving existing carbon stock and

ensuring a carbon flux results in net removals.

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Summary

Bozeman’s 2020 GHG inventory illustrates the City’s

progress toward its climate goals. Although Bozeman’s

emissions have increased by 5% since the 2008

baseline, the City’s emissions decreased 10% from

the most recent inventory in 2018 and per capita

emissions declined by 18%. While this decrease may

be attributable to the COVID-19 pandemic, the practical

outcome is that the Bozeman community contributed

fewer greenhouse gas emissions to the atmosphere in

2020.

With accelerated emissions reductions, there is still an

opportunity to achieve our community climate goals

under the adopted framework of the 2020 Bozeman

Climate Plan, which features solutions and actions to

transition to low-carbon energy and transportation

systems, pedestrian-oriented neighborhoods, and

nature-based solutions for urban cooling and disaster

resilience.

Measuring emissions helps Bozeman track progress

and understand new opportunities to reduce our

contribution to climate change. Monitoring emissions

also builds an understanding of areas where we have

agency, and areas that may require partnerships and

collaboration.

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Appendix A: Data Sources

Table 5. Emissions data sources and if they were calculated or estimated in this report.

Emissions Source

Data Source

Were Emissions Calculated or

Estimated?

Building Electricity Use NorthWestern Energy Calculated

Building Natural Gas Use NorthWestern Energy Calculated

Building Propane Use Amerigas Calculated

Building Stationary Diesel Use

US Census ACS House heating Fuel

Survey data, Bozeman commercial

square footage data, CBECS data,

Estimated

and US EIA unit conversions

Fugitive Emissions from Natural Gas GPC Protocol default leakage rate

Leakage

(0.3%)

Calculated

Transmission & Distribution Losses NorthWestern Energy loss rate Calculated

Vehicle Miles Traveled

City of Bozeman and Montana Dept

or Transportation

Calculated

Vehicle Registrations

EPA State Inventory Tool Mobile

Combustion Module

Calculated

Electric Vehicle Registrations Atlas EV Dashboard Calculated

EV Transmission & Distribution Losses NorthWestern Energy loss rate

Calculated

Transit Fuel Use

Human Resources Development

Council

Calculated

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Aviation Fuel Use

Emissions Source

Waste and compost tonnage

Closed landfill emissions

Waste transport, collection, and

processing emissions

Wastewater

Refrigerant Leaks

NorthWestern Energy Electric

Emissions Factor

Data Source

Bozeman/Yellowstone International

Airport

Gallatin County Solid Waste, City of

Bozeman

Estimated emissions depreciation

rate via ICLEI

GPC Protocol methodology

City of Bozeman data for Bozeman

WRF

Estimated from commercial square

footage and standard assumptions

and methodology from IPCC

NorthWestern Energy

Were Emissions Estimated or

Calculated?

Calculated

Calculated

Estimated

Calculated

Calculated

Estimated

N/A

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Appendix B: Emissions Factors

See Table 6 for an overview of the emission factors that were used for calculations throughout the inventory. The

Notes column provides details as to which emission factors need updated regularly.

Table 6. Summary of greenhouse gas emissions factors.

Stationary Energy Emission Factors—Electricity & Natural Gas

Emission Source GHG Value Unit Source Notes

Electricity

CO 2

0.419

CH 4

0.00003

N 2

O 0.000004

mt CO 2

/

MWh

mt CH 4

/

MWh

mt N 2

O/

MWh

Shown in NorthWestern Energy’s ESG/

Sustainability Template under Montana

Generation Statistics: Montana Owned +

Long Term Contracts for 2020. See line

7.3.2.3 on page 10.

EPA's eGrid: eGRID 2020 summary tables,

table 1, sub region NWPP.

Verify with each

inventory. Likely

that the CO 2

emission factor

will change

annually.

Verify with each

inventory.

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Stationary Energy Emission Factors—Electricity & Natural Gas

Emission Source GHG Value Unit Source Notes

CO 2

0.0053

mt CO 2

/

therm

Natural Gas CH 4

0.0000005

mt CH 4

/ 2013 ICLEI US Community Protocol,

therm

Appendix C.

N 2

O 0.00000001

mt N 2

O/

therm

CO 2

0.01

mt CO 2

/ ICLEI’s U.S. Community Protocol for

gallon Accounting and Reporting of Greenhouse

mt CH Gas Emissions (Community Protocol) –

CH 4

0.0000004

4

/

gallon Appendix C: Built Environment Emission Verify with each

Stationary Diesel

Activities and Sources, Version 1.1, July inventory.

N 2

O 0.0000001

generators by the industrial sector.

mt N 2

O/ 2013. Assumes distillate fuel oil number

gallon 2 and that diesel is primarily used in

Propane

CO 2

0.006

CH 4

0.000001

N 2

O 0.0000001

mt CO 2

/

gallon

mt CH 4

/

gallon

mt N 2

O/

gallon

ICLEI’s U.S. Community Protocol for

Accounting and Reporting of Greenhouse

Gas Emissions (Community Protocol) –

Appendix C: Built Environment Emission

Activities and Sources, Version 1.1, July

2013.

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Transportation Emission Factors—Ethanol, Gasoline, and Diesel

Emission Source GHG Value Unit Source Notes

CO 2

0.00878

mt CO 2

/

gal

Gasoline

CH 4 Varies by

N 2

O vehicle

g/mile

Diesel

Ethanol

CO 2

0.01

CH 4

N 2

O

Varies by

vehicle

CO 2

0.006

CH 4

N 2

O

Varies by

vehicle

mt CO 2

/

gal

g/mile

mt CO2/

gal

g/mile

EPA estimates as recommended by ICLEI.

Based on vehicles that are 2008 to present

or 2009 to present. Past years utilized ICLEI

Appendix D numbers.

Should remain

constant but

verify with each

inventory.

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Transit Emission Factors

Emission Source GHG Value Unit Source Notes

CO 2

0.01

mt CO 2

/

gal

Should remain

Diesel CH 4

0.001

g CH 4

/

constant but

EPA estimates as recommended by ICLEI.

mile

verify with each

N 2

O 0.0015

g N 2

O/

inventory.

mile

Aviation Emission Factors

CO 2

9.75

Kg CO 2

/

gal

Jet fuel CH 4

0.41

g CH4/

gal

Aviation Gasoline

N 2

O 0.08

CO 2

8.31

CH 4

0.36

N 2

O 0.07

g N2O/

gal

kg CO2/

gal

g CH4/

gal

g N2O/

gal

Per guidance from ICLEI on emissions

factors used in the ClearPath tool.

Should remain

constant but

verify with each

inventory.

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Waste Emission Factors

Emission Source GHG Value Unit Source Notes

Municipal Solid

Varies by mt CH4/ ton 2013 ICLEI US Community Protocol,

CH

Waste

4

waste type waste

Appendix E.

CH 4

mt CH4/ ton

waste

Recycled Waste

Composted

Waste

N 2

O

Varies by

waste type

CH 4

0.00047

N 2

O 0.00022

CH 4

0.00018

N 2

O 0.00013

mt N2O/

wet short

ton waste

mt CH 4

/ ton

waste

mt N2O/

ton waste

mt CH 4

/ ton

waste

mt N2O/

ton waste

CLEI’s U.S. Community Protocol for

Accounting and Reporting of Greenhouse

Gas Emissions (Community Protocol) –

Appendix C: Built Environment Emission

Activities and Sources, Version 1.1, July

2013.

Documentation for Greenhouse Gas

Emissions and Energy Factors Used in the

Waste Reduction Model (WARM). Assumes

green waste. Values are adjusted to CH4

and N2O emission factors.

Documentation for Greenhouse Gas

Emissions and Energy Factors Used in the

Waste Reduction Model (WARM). Assumes

biowaste. Values are adjusted to CH4 and

N2O emission factors.

Should

remain

constant

but verify

with each

inventory.

Wastewater

CH 4

N 2

O

Varies by

treatment

Varies

2013 ICLEI US Community Protocol,

Appendix F.

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Photo Credits

Page ES-1 Trevor Vannoy on Unsplash

Page 1 Lee Peters on Unsplash

Page 4 Chris Montgomery on Unsplash

Page 5 Jennifer Horstmann on Unsplash

Page 15 Matthew Lancaster on Unsplash

Page 17 Anna Gur on Unsplash

Page 21 Bobby Stevenson on Unsplash

Page 28 Matthew Lancaster on Unsplash

Page 32, 40 Olena Sergienko on Unsplash

Page 36 Malachy Marshall on Unsplash

Page 37 Trevor Vannoy on Unsplash

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