Carbon offsets: What Duke bought to get over two-thirds of the way to carbon neutrality

Duke recently achieved carbon neutrality — but this doesn’t mean the University’s emissions equal zero.

In reality, this historic achievement was made possible by both emissions reductions and the purchase of $4 million in carbon offsets.

As of fiscal year 2022, Duke’s carbon emissions reductions since 2007 were measured at 43%. The University expected to reduce emissions by another 2% in advance of the 2024 carbon neutrality deadline, leaving 55% to be offset by redeeming carbon credits. However, emissions ended up rising 11.35%, requiring Duke to offset almost 69% of its 2007-level emissions with carbon credits.

But what actually are carbon offsets and credits, how do they factor into an institution’s overall sustainability and how did Duke’s offsets portfolio come together?

How do offsets work?

The fundamental principle behind carbon offsets and carbon credits is the idea that although many institutions want to limit the amount of greenhouse gases (GHGs) they emit into the atmosphere since they have been linked to climate change, it’s not feasible to completely eradicate all emissions.

“No institution, no company is going to be carbon neutral without using carbon offsets,” said Matthew Arsenault, assistant director of carbon and sustainability operations. “There’s literally no way to reduce your emissions actually to zero.”

He also pointed to basic operational needs like electricity for powering lights and electronic devices, explaining that their usage can be reduced but not eliminated entirely. As a result, institutions that want to achieve full carbon neutrality must invest in alternatives: carbon credits and offsets.

Relying in part on offsets is standard practice. All 13 of the other U.S. colleges and universities that have achieved carbon neutrality so far have included offsets as part of their approach.

While Duke did purchase significantly more total carbon credits at 232,472 than these other schools, which tended to buy credits within the 1,000 to 40,000 range, that number is not disproportionately high. Duke is “by far the largest in terms of student population and greenhouse gas emissions” of the 14 carbon neutral institutions, as the others represent “smaller and more specialized” schools.

The balance between the emissions an institution reduces and the emissions an institution offsets with purchased credits also varies widely among the 14 schools. For example, when Allegheny College achieved carbon neutrality in 2020, offsets accounted for roughly 50% of its initial 2007-level emissions. When Bates College did so in 2019, offsets made up only 5% of the final count, as the institution had been able to slash 95% of its baseline 2001-level emissions.

Measuring Duke’s emissions

To get to the net-zero goal, institutions must start by measuring their total emissions.

Duke first began this process in 2007, through what Arsenault termed a University-wide “greenhouse gas inventory system” that involves partnerships between Sustainable Duke and stakeholders across campus. Individual offices and departments report information on their operations — such as how much gas is purchased for Duke’s fleet of buses or how much electricity is used by a particular building — which in turn allows sustainability office employees to determine the carbon emissions associated with those activities.

In 2007, the first year for which emissions data is recorded, Duke produced roughly 338,828 million tonnes of carbon dioxide equivalent (MT eCO2) — a standard metric for counting emissions that expresses the range of greenhouse gases in terms of carbon dioxide to make measuring their aggregate impact on the climate easier.

Duke’s emissions — along with those of hundreds of other colleges and universities — are reported through a Sustainability Indicator Management and Analysis Platform (SIMAP) maintained by the University of New Hampshire’s Sustainability Institute.

That initial number has since gone down, in large part because of intentional efforts to improve energy efficiency on campus. The COVID-19 pandemic also contributed to subsequent drops in 2020 and 2021 — when the University recorded its lowest emissions at roughly 171,808 MT eCO2 — as air travel plummeted and campus operations were reduced.

Emissions have crept back up since then, though they remain below the initial 2007 amount. In 2024, Duke’s total emissions measured just under 2019 levels at 232,472 MT eCO2.

Turning to offsets

That’s where carbon offsets and credits come in. Institutions can purchase these carbon accounting units to “cancel out” any lingering emissions and even out their balance sheet, which is exactly what Duke did this year.

Duke has invested largely in carbon offsets, supporting projects that decrease the amount of GHGs in the atmosphere to balance out University emissions that cannot be curtailed.

In 2009, the administration established the Duke Carbon Offsets Initiative (DCOI), the first university-based offsets program in the country. Arsenault explained that the initiative was created in response to the American College and University Presidents’ Agreement, which was signed in 2007 by then-President Richard Brodhead and committed Duke to its 2024 carbon neutrality goal. A more comprehensive climate strategy for the University — including a plan for investing in carbon offsets — was outlined in a 2009 Climate Action Plan.

University staff worked to amass a wide portfolio of offsets, which includes purchased offsets from external sources in addition to projects Duke had a hand in developing.

In the DCOI’s early years, staff focused mainly on developing new projects. Duke’s first endeavor was a waste-to-energy project project at a hog farm in Yadkinville, N.C., just over 100 miles west of campus. There, professors in the Pratt School of Engineering and Nicholas School of the Environment contributed to an effort to turn methane — a GHG produced as a byproduct of the farm’s regular operations — into usable electricity. Because that methane was prevented from entering the atmosphere, the University was able to purchase carbon credits from the successful project.

Other such efforts supported by Duke have included residential energy efficiency improvements, urban tree plantings, regenerative animal grazing projects and residential solar installments.

In later years, Duke pivoted away from these University-directed offset investments, knowing that the 2024 carbon neutrality deadline was fast approaching and that the staff’s time would be better spent in search of larger projects.

The DCOI, which merged with Sustainable Duke in 2022 and is now housed under the recently established Office of Climate and Sustainability, found one such project in Ohio and Thailand. An international company based out of both Bowling Green and Bangkok working to safely destroy refrigerants — which contain hydrochlorofluorocarbons (HCFCs), potent GHGs that can leak into the atmosphere when stored improperly or left for extensive periods of time — provided Duke with many of the credits included in its 2024 net emissions statement.

Ultimately, nearly 80% of the offset portfolio Duke cashed in for 2024 was made up of projects targeting ozone-depleting substances, like the HCFC-containing refrigerants. Most of the remaining 20% is accounted for by two methane-capture projects that operate similarly to the Yadkinville hog farm, this time using GHGs produced at a dairy farm and a landfill.

Quality control

Purchased offsets, where Duke was not involved in the actual carbon removal/reduction process, undergo a rigorous verification process to ensure they are ethical and of high quality.

“There are definitely problems in the carbon market, and so we were extremely careful to make sure that Duke was only investing in the projects that reflect our values,” Arsenault said.

Duke partnered with Ruby Canyon Environmental, Inc., which is known as a “registered verifier” — a company that “is registered on the carbon markets to go evaluate projects” — to help vet prospective offset investments. Together, they developed an evaluation tool for the University.

“It’s really just a huge Excel spreadsheet that forces us to ask ourselves really in-the-weeds, detailed questions about each individual project,” Arsenault said. “… It’s like this guided tour of an offset project where we’re asking questions, matching that with the information we have on a project and then scoring that project.”

Arsenault explained that certain questions are weighted higher than others, depending on the University’s priorities. He identified “additionality” as one of Duke’s primary interests, which means that the carbon emissions offset by the project would not have been removed or reduced if the project did not happen.

“It has to be this change in behavior,” Arsenault said. “… We were concerned that a lot of projects on the carbon market [were] things that were going to happen anyway, and people were treating it as … a way for them to just make a little more money from something they were planning on doing anyway.”

Permanence was another of the University’s priorities — ensuring that the offset projects Duke invests in represent a long-term commitment to lowered emissions.

Arsenault estimated that fewer than 10% of prospective offsets make it past the first round of evaluation. Those that remain are brought to an advisory committee of faculty and students with a “diverse range of backgrounds and sets of expertise” who further evaluate the legitimacy and quality of each project. Projects that are approved by the committee are ultimately recommended for purchase by the University.

What’s next?

The University is currently in the process of determining its “next-generation” climate goal, and conversations about what that will look like are occurring throughout the academic year.

Part of the work will include looking at how to maintain Duke’s carbon-neutral status past 2024, now that many of the University’s offsets have been “retired.” The administration is also looking into expanding the scope of its carbon tracking system, since significant portions of the larger “Duke” enterprise — notably, the health system and international campuses like Duke Kunshan University — were not included in 2024 metrics.

The University is also looking at how to reduce the amount of offsets it must purchase over time. Work continues on further lowering on-campus emissions, and a new solar facility intended to provide Duke with renewable energy is slated for completion in 2025.

For the time being, though, offsets remain a critical component of Duke’s commitment to the climate.

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