About

William Clark is the Harvey Brooks Research Professor of International Science, Public Policy and Human Development at Harvard University’s John F. Kennedy School of Government. Trained as an ecologist, his research focuses on sustainability science, which involves understanding the interactions of human and environmental systems with the goal of advancing sustainable development. He is particularly interested in how institutional arrangements influence the linkage between knowledge and action in the sustainability arena. At Harvard, he co-directs the Sustainability Science Program. He has co-authored and edited several influential publications, including 'Pursuing Sustainability: A Guide to the Science and Practice,' 'Adaptive Environmental Assessment and Management,' and 'Redesigning Rural Development.' Clark has also contributed to the field through his role as co-chair of the US National Research Council’s study 'Our Common Journey: A Transition Toward Sustainability.' He serves on the editorial board of the Proceedings of the National Academy of Science and is an elected member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Association for the Advancement of Science. His numerous awards include the MacArthur Prize, the Humboldt Prize, and teaching excellence awards from Harvard Kennedy School and Harvard College.

Research topics

• Political science
• Business
• Environmental resource management
• Environmental planning
• Medicine

Selected publications

• Chromatic numbers with open and nonzero local modular constraints

  ArXiv.org · 2025-09-06

  preprintOpen access

  In this paper, we explore chromatic numbers subject to various local modular constraints. For fixed $n$, we consider proper integer colorings of a graph $G$ for which the closed and open neighborhood sums have nonzero remainders modulo $n$ and provide bounds for the associated chromatic numbers $χ_n(G)$ and $χ_{(n)}(G)$, respectively. In addition, we provide bounds for $χ_{(n,k)}(G)$, the minimal order of a proper integer coloring of $G$ with open neighborhood sums congruent to $k\mod n$ (when such a coloring exists) as well as precise values for certain families of graphs.

  PublisherOA PDFDOI

• Author response for "Air quality impacts of electricity purchase and air travel by organizations"

  2025-10-16

  peer-review
  PublisherDOI

• Air quality impacts of electricity purchase and air travel by organizations

  2025-07-25

  preprintOpen access

  Organizational climate actions often prioritize greenhouse gas reductions without considering other impacts such as improved air quality from reduced fossil fuel use. While air quality benefits of large-scale policies are well studied, those of organization-level activities are more uncertain. We quantify the impact of organizations' fossil fuel use from electricity purchasing and air travel on climate and air quality using a system-level approach, with data from two universities and one corporation based in greater Boston. We use energy system and aviation emission models to estimate marginal emissions of greenhouse gases and air pollution precursors, and compare monetized air quality impacts calculated using an atmospheric chemistry-transport model with climate impacts from the same activities. Organizational activities were associated with air quality damages of ~$88/tCO2 (electricity purchase) and ~$265/tCO2 (air travel), compared to ~$170–200/tCO\2 in climate damages (2015 USD). Air quality impacts vary spatially, with renewable energy purchases and short-haul flight segments having proportionally more impacts in the US Northeast. Activities with the same CO2 emissions can have very different overall monetized benefits, suggesting organizations seeking broader sustainability impacts should consider air quality alongside direct climate impacts.

  PublisherDOI

• Chromatic numbers with closed local modular constraints

  ArXiv.org · 2025-03-01

  preprintOpen access

  Generalizing the notion of odd-sum colorings, a $\mathbb{Z}$-labeling of a graph $G$ is called a closed coloring with remainder $k\mod n$ if the closed neighborhood label sum of each vertex is congruent to $k\mod n$. If such colorings exist, we write $χ_{n,k}(G)$ for the minimum number of colors used for a closed coloring with remainder $k\mod n$ such that no neighboring vertices have the same color. General estimates for $χ_{n,k}(G)$ are given along with evaluations of $χ_{n,k}(G)$ for some finite and infinite order graphs.

  PublisherOA PDFDOI

• Air quality impacts of electricity purchase and air travel by organizations

  Environmental Research Letters · 2025-12-01

  articleOpen access

  Abstract Organizational climate actions often prioritize greenhouse gas reductions without considering other impacts such as improved air quality from reduced fossil fuel use. While air quality benefits of large-scale policies are well studied, those of organization-level activities are more uncertain. We quantify the impact of organizations’ fossil fuel use from electricity purchasing and air travel on climate and air quality using a system-level approach, with data from two universities and one corporation based in greater Boston. We use energy system and aviation emission models to estimate marginal emissions of greenhouse gases and air pollution precursors, and compare monetized air quality impacts calculated using an atmospheric chemistry-transport model with climate impacts from the same activities. Organizational activities were associated with air quality damages of $88 (54–123)/tCO 2 (electricity purchase) and $265 (192–337)/tCO 2 (air travel), compared to ∼$170–200/tCO 2 in climate damages (2015 USD). Air quality impacts vary spatially, with renewable energy purchases and short-haul flight segments having proportionally more impacts in the US Northeast. Activities with the same CO 2 emissions can have very different overall monetized benefits, suggesting organizations seeking broader sustainability impacts should consider air quality alongside direct climate impacts.

  PublisherDOI

• Chromatic Numbers with Closed Local Modular Constraints

  SSRN Electronic Journal · 2025-01-01

  preprintOpen access
  PublisherDOI

• Migrants can be a transformative force for sustainable development

  2024-01-18

  articleOpen access

  Drawing on findings from a PNAS Special Feature on Migration and Sustainability, organized by the authors and available (OA) here: https://www.pnas.org/topic/554

  PublisherOA PDFDOI

• Modeling Dynamic Systems for Sustainable Development 

  2024-03-09

  preprintOpen accessSenior author

  We summarize recent progress in dynamic modeling of nature-society systems to inform efforts towards sustainable development.  Drawing on lessons learned from a series of virtual workshops and a journal Special Feature, we identify and highlight examples of novel methods and advances, focusing on four stages of modeling practice -- defining purpose, selecting components, analyzing interactions, and assessing interventions. We highlight insights for researchers interested in assessing the implementation of system-wide sustainability strategies, with a focus on human well-being as an overarching objective, including methods that incorporate nature-society interactions into sectoral decision-support models, simulating cross-sector connections and differing contexts, and implementing computational and statistical approaches that evaluate decision scenarios under uncertainty. We additionally highlight techniques that can serve to foreground issues of power differentials among actors, including methods that can capture diverse societal actions and their agency, and incorporate different perspectives and normative visions. As a concrete example of the utility of a set of methods and advances from this survey of coupled nature-society systems modeling, we show how advances in computational techniques can be used to assess the degree to which national-scale climate policies in the United States can impact air pollution exposure to different racial/ethnic groups. 

  PublisherDOI

• Migration and sustainable development

  Proceedings of the National Academy of Sciences · 2024-01-08 · 49 citations

  articleOpen accessSenior author

  To understand the implications of migration for sustainable development requires a comprehensive consideration of a range of population movements and their feedback across space and time. This Perspective reviews emerging science at the interface of migration studies, demography, and sustainability, focusing on consequences of migration flows for nature-society interactions including on societal outcomes such as inequality; environmental causes and consequences of involuntary displacement; and processes of cultural convergence in sustainability practices in dynamic new populations. We advance a framework that demonstrates how migration outcomes result in identifiable consequences on resources, environmental burdens and well-being, and on innovation, adaptation, and challenges for sustainability governance. We elaborate the research frontiers of migration for sustainability science, explicitly integrating the full spectrum of regular migration decisions dominated by economic motives through to involuntary displacement due to social or environmental stresses. Migration can potentially contribute to sustainability transitions when it enhances well-being while not exacerbating structural inequalities or compound uneven burdens on environmental resources.

  PublisherOA PDFDOI

• Scientific frontiers on migration and sustainability

  Proceedings of the National Academy of Sciences · 2024-01-08 · 8 citations

  articleOpen accessSenior author

  This article introduces a Special Feature on Migration and Sustainability, organized by the authors. The full SF is available (OA) here: https://www.pnas.org/topic/554

  PublisherOA PDFDOI

Recent grants

• Integrating knowledge and policy for the management of natural resources in international development: The role of boundary organizations

  NSF · $334k · 2006–2009

Frequent coauthors

• Nancy M. Dickson

  Volkswagen Foundation

  39 shared

• Alicia G. Harley

  27 shared

• H. R. Hulpieu

  20 shared

• Henry D. Jacoby

  Massachusetts Institute of Technology

  18 shared

• M. Granger Morgan

  17 shared

• Jill Jäger

  Deutsches Institut für Urbanistik

  17 shared

• Ann Fisher

  16 shared

• Thomas J. Wilbanks

  Oak Ridge National Laboratory

  16 shared

Education

• PhD, Zoology

  University of British Columbia

  1979

• BSc

  Yale College

  1971

Awards & honors

• MacArthur Prize
• Humboldt Prize
• Kennedy School’s Carballo Award for excellence in teaching
• Harvard College Phi Beta Kappa Prize for Excellence in Teach…