Skip to main content
  • Submit
  • About
    • Editorial Board
    • PNAS Staff
    • FAQ
    • Accessibility Statement
    • Rights and Permissions
    • Site Map
  • Contact
  • Journal Club
  • Subscribe
    • Subscription Rates
    • Subscriptions FAQ
    • Open Access
    • Recommend PNAS to Your Librarian
  • Log in
  • My Cart

Main menu

  • Home
  • Articles
    • Current
    • Special Feature Articles - Most Recent
    • Special Features
    • Colloquia
    • Collected Articles
    • PNAS Classics
    • List of Issues
  • Front Matter
  • News
    • For the Press
    • This Week In PNAS
    • PNAS in the News
  • Podcasts
  • Authors
    • Information for Authors
    • Editorial and Journal Policies
    • Submission Procedures
    • Fees and Licenses
  • Submit
  • About
    • Editorial Board
    • PNAS Staff
    • FAQ
    • Accessibility Statement
    • Rights and Permissions
    • Site Map
  • Contact
  • Journal Club
  • Subscribe
    • Subscription Rates
    • Subscriptions FAQ
    • Open Access
    • Recommend PNAS to Your Librarian

User menu

  • Log in
  • My Cart

Search

  • Advanced search
Home
Home

Advanced Search

  • Home
  • Articles
    • Current
    • Special Feature Articles - Most Recent
    • Special Features
    • Colloquia
    • Collected Articles
    • PNAS Classics
    • List of Issues
  • Front Matter
  • News
    • For the Press
    • This Week In PNAS
    • PNAS in the News
  • Podcasts
  • Authors
    • Information for Authors
    • Editorial and Journal Policies
    • Submission Procedures
    • Fees and Licenses

New Research In

Physical Sciences

Featured Portals

  • Physics
  • Chemistry
  • Sustainability Science

Articles by Topic

  • Applied Mathematics
  • Applied Physical Sciences
  • Astronomy
  • Computer Sciences
  • Earth, Atmospheric, and Planetary Sciences
  • Engineering
  • Environmental Sciences
  • Mathematics
  • Statistics

Social Sciences

Featured Portals

  • Anthropology
  • Sustainability Science

Articles by Topic

  • Economic Sciences
  • Environmental Sciences
  • Political Sciences
  • Psychological and Cognitive Sciences
  • Social Sciences

Biological Sciences

Featured Portals

  • Sustainability Science

Articles by Topic

  • Agricultural Sciences
  • Anthropology
  • Applied Biological Sciences
  • Biochemistry
  • Biophysics and Computational Biology
  • Cell Biology
  • Developmental Biology
  • Ecology
  • Environmental Sciences
  • Evolution
  • Genetics
  • Immunology and Inflammation
  • Medical Sciences
  • Microbiology
  • Neuroscience
  • Pharmacology
  • Physiology
  • Plant Biology
  • Population Biology
  • Psychological and Cognitive Sciences
  • Sustainability Science
  • Systems Biology
Letter

Reply to Sutton et al.: Relationship between temperature and conflict is robust

Marshall B. Burke, Edward Miguel, Shanker Satyanath, John A. Dykema, and David B. Lobell
PNAS June 22, 2010 107 (25) E103; https://doi.org/10.1073/pnas.1005748107
Marshall B. Burke
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: marshall.burke@berkeley.edu
Edward Miguel
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Shanker Satyanath
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
John A. Dykema
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
David B. Lobell
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • Article
  • Info & Metrics
  • PDF
Loading

In a recent paper, we documented strong historical linkages between temperature and civil conflict in Africa (1). Sutton et al. (2) raise two concerns with our findings: that the relationship between temperature and war is based on common trends and is therefore spurious, and that our model appears overly sensitive to small specification changes. Both concerns reflect a basic misunderstanding of the analysis.

In particular, Sutton et al. (2) worry that temperature might either “proxy” for other causal variables or be correlated over time with other unrelated processes that also affect civil war. The effect of temperature on war clearly occurs through some intermediate channel, and we argue for the likely role of precisely the variables that Sutton et al. (2) mention (soil moisture and agricultural productivity). High temperatures tend to reduce African crop yields and depress rural incomes (3), declines that many benchmark studies implicate in the incidence of civil war (4). However, because variables such as income both affect and are affected by civil conflict, including them directly as regressors is problematic (5), and thus proxy variables (what economists call instrumental variables) (6) must be used. The fact that temperature is a strong instrument for African economic outcomes underpins—rather than undermines—our study.

Furthermore, our econometric approach deals directly with the concern that temperature might be correlated over time with other explanatory variables: we identify the effects of temperature on conflict through year-to-year deviations from country-level average temperature, which are unlikely to be spuriously correlated to unrelated social phenomena. We control for the influence of unrelated trending variables using country-specific time trends that account for trends in conflict finance, decolonization, or any other time-varying unobservable of concern. That our temperature coefficient is robust to inclusion of these time trends suggests that temperature is indeed causal.

The second concern of Sutton et al. (2) is the apparent “fragility” of the statistical models we present, evidenced by changes in R2 across the model specifications shown in ref. 1, table 1. The simple explanation for these changes is listed in the table caption: models 1 and 2 use different control variables than model 3. In particular, models 1 and 2 include country-specific time trends as control variables, whereas model 3 instead uses explicit controls for regime type and income. Because country-specific time trends will pick up the influence of all time-trending variables, models 1 and 2 will soak up more of the variation in our dependent variable and thus yield a higher model R2.

Our paper does not argue that temperature is the only—or even the primary—determinant of civil war. Further work is needed to understand how climate affects civil war, and we note this clearly in our paper. The conclusion of Sutton et al. (2) that our study might “discourage meaningful engagement” is curious given the explicit suggestions for public policy engagement we offer in the paper’s conclusion. The temperature effects we document only make the identification of proper engagement strategies more important. We feel that our paper is a contribution to that effort.

Footnotes

  • 1To whom correspondence should be addressed. E-mail: marshall.burke{at}berkeley.edu.
  • Author contributions: M.B.B., E.M., S.S., J.A.D., and D.B.L. designed research, performed research, analyzed data, and wrote the paper.

  • The authors declare no conflict of interest.

    View Abstract

    References

    1. ↵
      1. Burke MB,
      2. Miguel E,
      3. Satyanath S,
      4. Dykema JA,
      5. Lobell DB
      (2009) Warming increases the risk of civil war in Africa. Proc Natl Acad Sci USA 106:20670–20674.
      OpenUrlAbstract/FREE Full Text
    2. ↵
      1. Sutton A,
      2. et al.
      (2010) Does warming increase the risk of civil war in Africa? Proc Natl Acad Sci USA 107:E102.
      OpenUrlFREE Full Text
    3. ↵
      1. Schlenker W,
      2. Lobell DB
      (2010) Robust negative impacts of climate change on African agriculture. Environ Res Lett, 10.1088/1748-9326/5/1/014010.
    4. ↵
      1. Collier P,
      2. Hoeffler A
      (2004) Greed and grievance in civil war. Oxf Econ Pap 56:563–595.
      OpenUrlCrossRef
    5. ↵
      1. Miguel E,
      2. Satyanath S,
      3. Sergenti E
      (2004) Economic shocks and civil conflict: An instrumental variables approach. J Polit Econ 112:725–753.
      OpenUrlCrossRef
    6. ↵
      1. Wooldridge JM
      (2002) Econometric Analysis of Cross Section and Panel Data (MIT Press, Cambridge, MA).
    PreviousNext
    Back to top
    Article Alerts
    Email Article

    Thank you for your interest in spreading the word on PNAS.

    NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. We do not capture any email address.

    Enter multiple addresses on separate lines or separate them with commas.
    Reply to Sutton et al.: Relationship between temperature and conflict is robust
    (Your Name) has sent you a message from PNAS
    (Your Name) thought you would like to see the PNAS web site.
    CAPTCHA
    This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
    Citation Tools
    Reply to Sutton et al.: Relationship between temperature and conflict is robust
    Marshall B. Burke, Edward Miguel, Shanker Satyanath, John A. Dykema, David B. Lobell
    Proceedings of the National Academy of Sciences Jun 2010, 107 (25) E103; DOI: 10.1073/pnas.1005748107

    Citation Manager Formats

    • BibTeX
    • Bookends
    • EasyBib
    • EndNote (tagged)
    • EndNote 8 (xml)
    • Medlars
    • Mendeley
    • Papers
    • RefWorks Tagged
    • Ref Manager
    • RIS
    • Zotero
    Request Permissions
    Share
    Reply to Sutton et al.: Relationship between temperature and conflict is robust
    Marshall B. Burke, Edward Miguel, Shanker Satyanath, John A. Dykema, David B. Lobell
    Proceedings of the National Academy of Sciences Jun 2010, 107 (25) E103; DOI: 10.1073/pnas.1005748107
    Digg logo Reddit logo Twitter logo Facebook logo Google logo Mendeley logo
    • Tweet Widget
    • Facebook Like
    • Mendeley logo Mendeley
    Proceedings of the National Academy of Sciences: 107 (25)
    Table of Contents

    Submit

    Sign up for Article Alerts

    Jump to section

    • Article
      • Footnotes
      • References
    • Info & Metrics
    • PDF

    You May Also be Interested in

    Abstract depiction of a guitar and musical note
    Science & Culture: At the nexus of music and medicine, some see disease treatments
    Although the evidence is still limited, a growing body of research suggests music may have beneficial effects for diseases such as Parkinson’s.
    Image credit: Shutterstock/agsandrew.
    Scientist looking at an electronic tablet
    Opinion: Standardizing gene product nomenclature—a call to action
    Biomedical communities and journals need to standardize nomenclature of gene products to enhance accuracy in scientific and public communication.
    Image credit: Shutterstock/greenbutterfly.
    One red and one yellow modeled protein structures
    Journal Club: Study reveals evolutionary origins of fold-switching protein
    Shapeshifting designs could have wide-ranging pharmaceutical and biomedical applications in coming years.
    Image credit: Acacia Dishman/Medical College of Wisconsin.
    White and blue bird
    Hazards of ozone pollution to birds
    Amanda Rodewald, Ivan Rudik, and Catherine Kling talk about the hazards of ozone pollution to birds.
    Listen
    Past PodcastsSubscribe
    Goats standing in a pin
    Transplantation of sperm-producing stem cells
    CRISPR-Cas9 gene editing can improve the effectiveness of spermatogonial stem cell transplantation in mice and livestock, a study finds.
    Image credit: Jon M. Oatley.

    Similar Articles

    Site Logo
    Powered by HighWire
    • Submit Manuscript
    • Twitter
    • Facebook
    • RSS Feeds
    • Email Alerts

    Articles

    • Current Issue
    • Latest Articles
    • Archive

    PNAS Portals

    • Anthropology
    • Chemistry
    • Classics
    • Front Matter
    • Physics
    • Sustainability Science
    • Teaching Resources

    Information

    • Authors
    • Editorial Board
    • Reviewers
    • Librarians
    • Press
    • Site Map
    • PNAS Updates

    Feedback    Privacy/Legal

    Copyright © 2021 National Academy of Sciences. Online ISSN 1091-6490