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Greenhouse Gas Inventories

A greenhouse gas (GHG) inventory measures the emissions that are released into the atmosphere as a result of university operations. This analysis provides the metric to understand sources of greenhouse gas emissions and identify opportunities for reducing emissions. 

In 2023, Carnegie Mellon signed a Climate Commitment to eliminate or offset net greenhouse gas emissions by 2030. Even before becoming signatories, CMU conducted an annual GHG inventory. When reviewing progress, annual emissions are compared to the baseline year, 2005, which was the first year CMU conducted a GHG inventory.

GHG emissions chart from 2005-2025
Click the image to enlarge

For additional details, see CMU's GHG emission reports on Second Nature's reporting platform.

Greenhouse gas emission sources are defined as direct and indirect. The GHG Protocol defines these and categorizes emissions into three categories:

Scope 1 includes direct emissions that are physically produced on campus. These sources are “owned or directly controlled” by the institution.

CMU reports natural gas and fuel used by campus vehicles.

Scope 2 includes indirect emissions associated with purchased utilities required for campus operations. 

CMU reports purchased electricity and steam. Renewable energy is also included in this scope.

Note: steam purchased from Bellefield Boiler Plant was recharacterized from Scope 1 to Scope 2 starting in 2024 to better align with the GHG Protocol Accounting and Reporting Standard. CMU and the University of Pittsburgh now use the same approach for reporting Bellefield Boiler Plant steam purchases.

Scope 3 includes indirect emissions from sources that are not owned or controlled by the campus, but that are central to campus operations or activities. 

CMU reports emissions associated with student, faculty, and staff communiting and university-paid air travel, according to Second Nature's Climate Leadership Network guidance for Scope 3 reporting.

Emissions from these sources are matched with purchases of high-quality carbon credits, resulting in net zero emissions. See the section below for details on offset projects. 

Carnegie Mellon has reduced Scope 1 and 2 emissions by more than 70% since 2005. This reduction can be attributed to increased building efficiency as seen in the commitment to build new buildings to meet LEED Gold and by acquiring RECs equal to the university’s electricity use.