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Getting to Net Zero

By Dylan Walsh ’11 MEM

To avert the worst impacts of the climate crisis and realize a healthier, more sustainable future, we must achieve net-zero global carbon emissions by midcentury. Getting there will require rethinking and taking action in nearly every sector of the economy — from how and what we produce, to how we get around and what we consume. From Professor Daniel Esty, who is working with the World Trade Organization to develop a sustainability agenda for global trade, to Maggie Tallmadge ‘20 MEM, who is establishing industrial-scale renewable energy projects through Navajo Power, to PhD student Matt Ashenfarb, who is helping the Treasury Department track the outcomes of the Inflation Reduction Act, to Research Scientist Sara Kuebbing, who is developing innovative strategies to increase the carbon intake of forests on a gigaton scale, YSE faculty, students, and alumni are helping to solve what the United Nations Human Rights Council has called “the largest, most pervasive threat to the natural environment and human societies the world has ever experienced.”

An unprecedented level of innovation and highly diversified strategies will be needed if we are to stand a chance of succeeding; no single change or adjustment, no one technological breakthrough or novel policy mechanism will suffice to leap from where we are today — from a record-setting 40 billion tons of global carbon emissions in 2023 — to where we need be to achieve the ultimate goal of net-zero emissions no later than 2050. A 2021 roadmap to net zero released by the International Energy Agency, in fact, detailed 400 distinct milestones that would push the world’s net emissions down to zero by 2050. Each milestone is daunting in its own way, but the seven members of the YSE community profiled here manifest hope by being part of the concerted international march toward solutions.

Stephanie Carlisle

Constructing the Future: 
Stephanie Carlisle

The buildings and construction sector accounts for nearly 40% of energy-and process-related carbon dioxide emissions. The sector also has significant impacts on deforestation, habitat destruction, and species extinction. And while several efforts, such as LEED and Passive House — voluntary standards that focus on energy efficiency, comfort, and affordability in buildings — have drawn public attention to building operations, far less attention has been paid to the carbon embedded in buildings themselves. 

Embodied carbon from building materials and construction represents at least 11% of global carbon emissions, most of which can be attributed to three materials: concrete, iron, and steel. Given the rapid growth in urban construction around the world, the demand for these materials will only grow.

Stephanie Carlisle ’11 MEM, a lecturer at the Weitzman School of Design at the University of Pennsylvania and a senior researcher at the Carbon Leadership Forum, is working with colleagues to assess the climate impacts of the built environment while providing architects and engineers with tools that make it easier to mitigate these impacts. For example, a current project focuses on state and federal Buy Clean policies, which leverage the public sector’s immense purchasing power to promote the use of low-carbon construction materials. Carlisle and her team are working to define what, exactly, counts as “low carbon” in materials such as concrete or steel. She is also working with a consortium of teams funded by ARPA-E, the Department of Energy’s experimental research arm, to create novel carbon-storing materials for the construction sector, including bio-cements and mushroom-based materials.

Though Carlisle is enthusiastic about these and other projects she is working on, what excites her most is the growing community of like-minded architects, designers, engineers, and academics — groups such as the Structural Engineering Institute and the American Institute of Architects — that are committing to net-zero goals and crafting open-source tools that benefit the whole community. “No single building or firm is going to do this on its own, but the kinds of collaborations that we are seeing now could transform the whole industry,” she says.

Sara Kuebbing

Optimizing Forests: 
Sara Kuebbing

There are lots of different avenues for removing and storing carbon from the atmosphere: mineral weathering, enhanced ocean alkalinity, novel technologies, and good old-fashioned trees. Forests are the only current carbon capture “technology” that are widespread around the globe today.

As part of a consortium of institutions, Sara Kuebbing, the director of research for the Yale Applied Science Synthesis Program and a research scientist with the Yale Center for Natural Carbon Capture and YSE, helped draft the U.S. Department of Energy’s “Roads to Removal” report, a project led by Lawrence Livermore National Laboratory. The report seeks to answer the question of how much CO2 can be removed from the atmosphere by sequestration projects in the United States and at what cost. While half of the world’s above-ground carbon is stored by tropical ecosystems, Kuebbing focused on ways carbon capture could be enhanced in U.S.  temperate forests. She collaborated on a chapter examining U.S. forestry that offers three primary approaches to carbon sequestration: increase forestland by planting trees and stopping deforestation; increase the rate at which forests remove CO2 from the atmosphere; and increase the durability of forest carbon storage (by making forests more resilient to wildfires, for example).

Kuebbing and her co-authors present three case studies and find that by managing Western forests for fire resilience, Northeastern forests for sustainable harvesting, and planting Southeastern pine forests, nearly 2 billion metric tons of CO2 equivalent could be removed from the atmosphere by 2050.

Though plans for implementing forest management for climate mitigation are ready today, action has been slow, in part, Kuebbing says, because discussion around carbon capture can sometimes fixate on silver bullets: “I’ve gotten caught up in conversations about the best thing to do, about whether or not we’re making the best choice,” she says. “It’s been three decades since the adoption of the Kyoto Protocol, and we have not reduced fossil fuel emissions to keep the globe from reaching catastrophic warming. We now no longer have the luxury of a slow and methodical international approach to climate mitigation and instead need an all-hands-on-deck effort to reduce emissions and capture excess carbon from the atmosphere.”

Given the urgency and geographic specificity of forestry solutions, Kuebbing says cities and counties should be getting to work immediately on local initiatives that are feasible. Cities should be asking where they can plant trees; Western regions should be developing fire management plans; and so on. Not only could these actions pull carbon out of the atmosphere, but they could provide ancillary benefits such as habitat for wildlife, food for local economies, clean air and water, and the cultural, aesthetic, recreational, and spiritual services offered by wildland.

“Every day matters,” Kuebbing says. “We need to be doing and learning as we go.”

Daniel Esty

Greening Global Trade: 
Daniel Esty

The Marrakesh Agreement of 1994, which established the World Trade Organization (WTO), states several goals in its opening paragraph: raising standards of living; ensuring full employment, and allowing for the optimal use of the world’s resources in accordance with the objective of sustainable development, seeking both to protect and preserve the environment.

Thirty years later, a chorus of voices from all corners of the global economy is calling into question how effectively the WTO has upheld these goals. “The international trade system is seen as somewhat out of step with 21st-century values around climate change and a sustainable future more broadly,” says Daniel Esty, Hillhouse Professor of Environmental Law and Policy. And yet trade, done right, has potential to add speed and scale in the transition to a net-zero GHG emissions future.

Esty recently returned from a public service leave during which he worked with WTO Director-General Ngozi Okonjo-Iweala as she developed a sustainability agenda for the international trade system. In this role, Esty and a group of colleagues organized 10 workshops, each focused on a specific issue where “the trade system and sustainability came together — or sometimes crashed into each other,” he says. The workshops brought together academics, practitioners, and experts from industry and government to delve into areas ranging from the role of trade in promoting a circular economy to trade and food systems to trade and sustainable development finance.

The ideas from these workshops were then refined and shaped into a comprehensive trade system reform agenda that would position the WTO to assume a leading role in the fight against climate change and in support of a sustainable future more broadly. This agenda — the Villars Framework for a Sustainable Trade System — included items such as a fundamentally retooled approach to subsidies that takes into account sustainability impact; measurement protocols for greenhouse gas emissions associated with traded goods; and the establishment of an inclusive process for setting sustainability standards among goods. 

Though trade has largely been overlooked in discussion of climate change mitigation and adaptation, Esty, who has worked in this world for decades, is pleased to see it now gaining prominence. In December at COP28 in Abu Dhabi, UAE, there was a thematic trade day, the first one in COP’s history. It featured more than 100 events discussing how trade might help solve rather than exacerbate the climate crisis.

“Done properly, an agenda like this could help the trade system reconnect with public values around the world that are focused on sustainability as a core priority for 21st-century life,” Esty says. “Centering this in the work of the WTO will help make it fit for purpose going forward, delivering sustainable development in trade as a foundation for human thriving all over the world.”

Matt Ashenfarb

Growing Clean Investments: 
Matt Ashenfarb

The Inflation Reduction Act (IRA) was signed into law into the summer of 2022, marking the single largest investment in climate and energy in U.S. history. Teams of lawyers from agencies across the federal government were summoned to figure out how to translate the statutory text into policy. Tagging alongside these lawyers were a handful of researchers, among them Matt Ashenfarb, a YSE doctoral candidate in environmental economics who took leave from researching and writing his dissertation to work at the Department of the Treasury.

Ashenfarb is one of two academics working out of the Office of Climate and Energy Economics at the Treasury Department. There, he and his supervisor, Arik Levinson, professor of economics at Georgetown University, are studying the environmental and economic impacts of the IRA as associated funding begins flowing to state governments, municipalities, nonprofits, businesses, and individuals across the country. They want to know what effect this money has on local economies and the climate.

So far, the IRA — which Ashenfarb describes as “without a doubt the most consequential climate legislation our country has seen” — seems to be having an impact on economic and environmental fronts, as well as on equity; this is promising, given legislation doesn’t always perform as it is expected to. In one study, Ashenfarb and coauthors found that investment in clean energy projects roughly doubled in economically disadvantaged communities and “energy communities,” parts of the country typically reliant on fossil fuel production.

“The preliminary data suggest that IRA policies are working as intended,” Ashenfarb says. “Clean investments are growing everywhere, but particularly in those places that otherwise stood to lose most from the transition to a clean-energy economy.”

Stepping back from the specifics of the legislation, he notesh that the IRA is a strong signal of U.S. reengagement with global efforts to solve the climate crisis. He hopes this marks the beginning of a decades-long commitment. “This can’t be the end of U.S. climate policy if we want to meet our commitments in the Paris Climate Agreement,” he says. “But if we compare a world where the IRA exists to one where it doesn’t, we’re surely closer to our commitments in the world with the IRA.”

Sara Harari

Financing Sustainability: 
Sara Harari 

When Sara Harari ’19 MEM, MBA talks with students, there is one question that they ask her perhaps more than any other: how did she get the word “innovation” in her job title? She tells them that, in fact, the title is simply a formal recognition of the way she has always approached her vocation.

“Any job can be an innovation job,” says Harari, who is the associate director of innovation and strategic advisor to Bryan Garcia ’00 MEM, the president and CEO at the Connecticut Green Bank. Innovation is about doing something new, whether developing a technology or devising a business model or engaging with customers or crafting policy.

The Green Bank is a quasi-public agency that uses public money to attract private capital into the green economy. In her role, which she has held since 2021, Harari works on a wide range of projects. One she is particularly enthusiastic about is the statewide Innovative Energy Solutions Program. Sponsored by several Connecticut agencies, it provides up to $5 million per project in support of entrepreneurs and utilities in the pursuit of new technologies or policies that will affordably and equitably decarbonize the state’s electric grid.

All of Harari’s efforts — and those of the Green Bank broadly — received a huge boost with the passage of the federal Inflation Reduction Act of 2022. The Green Bank is eagerly anticipating the forthcoming announcement of awards from the Greenhouse Gas Reduction Fund, a $27 billion investment to mobilize financing and private capital to address the climate crisis; the bank has proposed myriad uses for this funding, including pursuing the electrification of Connecticut’s school bus fleet.

Electric school buses are roughly twice as expensive as conventional diesel buses, and, given relatively high electricity costs in Connecticut, they don’t necessarily promise operational savings. But they are far better for the environment and for public health, particularly in state-designated environmental justice communities. Figuring out how to make this conversion happen without unduly burdening municipal budgets is a thorny challenge. It includes creating new financial models and building collaborative partnerships between under-resourced school districts, third-party busing companies, and city governments. It also requires sorting out the utility side of the equation in managing the grid so it can support the daily charging requirements of an electric bus fleet.

All of this, Harari notes, must be done on a very tight timeline. Connecticut state policy mandates that every one of the 2,000 diesel buses in designated environmental justice communities be replaced with electric buses by 2030. The rest of the fleet is slated to be electrified by 2040.

“2030 is right around the corner,” Harari says. “But gnarly problems like this get me excited.”

Stafford Sheehan

Innovating to Scale:
Stafford Sheehan

In a way, the idea for Air Company, which transforms carbon dioxide into resources, was inspired by Thomas Edison, says Stafford Sheehan ’16 PhD. 

“Edison talked about making fuel from sunlight and water as plants do,” Sheehan says. “We’re using that same concept of deriving renewable fuels directly from CO2.  It’s artificial photosynthesis.”

Air Company, co-founded in 2017 by Sheehan, started with technology that he developed while a research associate at the Center for Green Chemistry and Green Engineering (CGCGE) at YSE. There, he “did some brilliant work developing catalysts that are very effective at splitting water into hydrogen and oxygen,” says Paul Anastas, Teresa and H. John Heinz III Professor in the Practice of Green Chemistry for the Environment. Anastas and Julie Zimmerman, deputy director for research at CGCGE and vice provost for Yale Planetary Solutions, supervised and mentored Sheehan while he was at the center. Sheehan and Anastas spun this technology into a company called Catalytic Innovations, which, in turn, became the foundation for Air Company. (Anastas is now the scientific advisor for Air Company.)

In short, Air Company is able to blend captured CO2 with hydrogen to manufacture a range of final products that are far more sustainable than their conventional counterparts. Drawing from a study done at Columbia University, Air Company found that scaling its technology across all relevant applications could avoid nearly 11% of global CO2 emissions. Reaching such scale, though, is no minor challenge.

“In chemical processing, economies of scale are super important,” Sheehan explains. “If you have a system the size of a truck, it might make ethanol for $1,000 per gallon, while if you have a refinery big enough to have its own zip code, then you can make that same product for $2 or $3 per gallon.”

To help build toward this scale, Sheehan and his co-founder, Gregory Constantine, started by selling high-end products that use their ethanol such as perfume and vodka. Later, they unveiled sustainable aviation fuel. They have partnered with the U.S. military to support efforts to achieve energy independence. Last year, Air Company secured a $65 million contract with the Department of Defense to de-risk and scale the company’s patented technology and fuels. They have also secured partnerships with JetBlue, Virgin Atlantic, Air Canada, and others to explore potential applications of the technology for decarbonizing the aviation industry.

The promise of Sheehan’s innovation extends far beyond spirits, fragrance, and sustainable aviation fuel, though. “The fact that you can turn CO2 into anything from vodka to aviation fuel means that this technology is broadly applicable,” Anastas says. “While we currently have a petroleum-based economy, it’s now possible to imagine turning CO2 into anything that we turn petroleum into.”

As Sheehan puts it, big change for the environment is achievable. “I can see it on the horizon.”

Maggie Tallmadge

Powering Clean Energy: 
Maggie Tallmadge

Though tribal lands of the continental United States have the potential to provide nearly 7% of U.S. renewable energy, when Maggie Tallmadge ’20 MEM, a citizen of the Cherokee Nation, looked into how much renewable energy they were actually producing, she found it was next to nothing. “I didn’t see many projects,” she says. “When I dug into why this was, I found that it came down to a lot of barriers preventing project development.”

For one thing, resource development was something that had always been done to Native American tribes, Tallmadge says, which created a vacuum of internal capacity. Many tribes also face challenges when trying to access capital, and the majority live in remote areas that lack the transmission infrastructure needed for large-scale renewable energy projects. Finally, regulatory hurdles, such as the need to draft impact statements in compliance with the National Environmental Policy Act, extend the permitting process by years and hobble partnerships, she says.

Navajo Power, where Tallmadge is currently the director of development, could be a model for addressing these concerns. The employee-owned, public benefits corporation is laying the foundation for utility-scale renewable development on tribal lands. “We’re the company that does all of the early, risky development,” she says. “We do site acquisitions, lease negotiations, permitting, interconnection, community relations, the activities that nobody else is invested in at scale on tribal lands.”

Navajo Power raises funding from philanthropy, private equity and debt markets, and development fees; it also forms strategic partnerships with other renewables developers. Eighty percent of profits are reinvested in local tribes and every project is designed hand in hand with tribal partners. “There is huge revenue potential for the tribe and the community,” Tallmadge says, “and huge employment potential.”

Though no projects have yet broken ground, several are in process. The most mature of these is the Painted Desert Solar Project, a 750-megawatt solar photovoltaic and battery storage plant sited in the Navajo Nation in Arizona. In total, Navajo Power has roughly three gigawatts of power under development.

Despite the company’s name, it works beyond the Navajo Nation. Part of Tallmadge’s job is creating ties and exploring opportunities in the Midwest and along the West Coast. She is also responsible for raising capital, whether through philanthropy or private equity, and for navigating relevant policy.

Her arrival at this job appears almost fated. Tallmadge describes how her grandmother was born in Indian Territory in the current state of Oklahoma the year that it entered the union — an admission that centered on oil rights intended for non-Native prospectors. In Tallmadge’s history are the shadows of fossil fuel extraction and colonialism.

“My father always raised me with gadugi, which is a Cherokee word that means essentially ‘to work together for the betterment of the community,’” Tallmadge says. “At Navajo Power, I feel like I’ve found my home.”