Table 1 Primary quantitative studies testing for a relationship between climate and conflict, violence, or political instability.

“Stat. test” is Y if the analysis uses formal statistical methods to quantify the influence of climate variables and uses hypothesis testing procedures (Y, yes; N, no). “Large effect” is Y if the point estimate for the effect size is considered substantial by the authors or is greater in magnitude than 10% of the mean risk level for a 1σ change in climate variables. “Reject β = 0” is Y if the study rejects an effect size of zero at the 95% confidence level. “Reject β = 10%” is Y if the study is able to reject the hypothesis that the effect size is larger than 10% of the mean risk level for a 1σ change in climate variables. –, not applicable. SSA, sub-Saharan Africa; PDSI; Palmer Drought Severity Index; ENSO, El Niño–Southern Oscillation; NAO, North Atlantic Oscillation; N. Hem., Northern Hemisphere.

StudySample
period
Sample
region
Time
unit
Spatial
unit
Independent
variable
Dependent
variable
Stat.
test
Large
effect
Reject
β = 0
Reject
β = 10%
Ref.
Interpersonal conflict (15)
Anderson et al. 2000*1950–1997USAAnnualCountryTempViolent crimeYYY(34)
Auliciems et al. 1995†1992AustraliaWeekMunicipalityTempDomestic violenceYYY(29)
Blakeslee et al. 20131971–2000IndiaAnnualMunicipalityRainViolent and
property crime
YYY(42)
Card et al. 2011†‡1995–2006USADayMunicipalityTempDomestic violenceYYY(37)
Cohn et al. 1997§1987–1988USAHoursMunicipalityTempViolent crimeYYY(30)
Jacob et al. 2007†‖1995–2001USAWeekMunicipalityTempViolent and
property crime
YYY(35)
Kenrick et al. 1986¶1985USADaySiteTempHostility YYY(27)
Larrick et al. 2011†‡‖1952–2009USADaySiteTempViolent retaliationYYY(36)
Mares 20131990–2009USAMonthMunicipalityTempViolent crimeYYY(39)
Miguel 2005†‡1992–2002TanzaniaAnnualMunicipalityRainMurderYYNN (40)
Mehlum et al. 20061835–1861GermanyAnnualProvinceRainViolent and
property crime
YYY(43)
Ranson 2012†‖1960–2009USAMonthCountyTempPersonal violenceYYY(38)
Rotton et al. 2000§1994–1995USAHoursMunicipalityTempViolent crimeYYY(31)
Sekhri et al. 2013†2002–2007IndiaAnnualMunicipalityRainMurder and
domestic violence
YYY(41)
Vrij et al. 1994¶1993NetherlandsHoursSiteTempPolice use of forceYYY(28)
Intergroup conflict (30)
Almer et al. 20121985–2008SSAAnnualCountryRain/tempCivil conflictYYNN(65)
Anderson et al. 20131100–1800EuropeDecadeMunicipalityTempMinority expulsionYYY(63)
Bai et al. 2010220–1839ChinaDecadeCountryRainTransboundaryYYY(50)
Bergholt et al. 2012‡#1980–2007GlobalAnnualCountryFlood/stormCivil conflictYNNY(75)
Bohlken et al. 2011‖#1982–1995IndiaAnnualProvinceRainIntergroup YYNN (44)
Buhaug 2010#1979–2002SSAAnnualCountryTempCivil conflictYNNN(22)
Burke 2012‡‖#1963–2001GlobalAnnualCountryRain/tempPolitical instabilityYYN** N(71)
Burke et al. 2009‡‖#††1981–2002SSAAnnualCountryTempCivil conflictYYY(64)
Cervellati et al. 20111960–2005GlobalAnnualCountryDroughtCivil conflictYYY(54)
Chaney 2011641–1438EgyptAnnualCountryNile floodsPolitical InstabilityYYY(70)
Couttenier et al. 2011#1957–2005SSAAnnualCountryPDSICivil conflictYYY(53)
Dell et al. 2012#1950–2003GlobalAnnualCountryTempPolitical instability
and civil conflict
YYY(21)
Fjelde et al. 2012‡#1990–2008SSAAnnualProvinceRainIntergroup YYN**N(55)
Harari et al. 2013#1960–2010SSAAnnualPixel (1°)DroughtCivil conflictYYY(52)
Hendrix et al. 2012‡‖#1991–2007SSAAnnualCountryRainIntergroup YYY(46)
Hidalgo et al. 2010‡‖#1988–2004BrazilAnnualMunicipalityRainIntergroupYYY(25)
Hsiang et al. 2011‖#1950–2004GlobalAnnualWorldENSOCivil conflictYYY(51)
Jia 20121470–1900ChinaAnnualProvinceDrought/floodPeasant rebellionYYY(56)
Kung et al. 20121651–1910ChinaAnnualCountyRainPeasant rebellionYYY(47)
Lee et al. 20131400–1999EuropeDecadeRegionNAOViolent conflictYYY(57)
Levy et al. 2005‡‖#1975–2002GlobalAnnualPixel (2.5°)RainCivil conflictYYN**N (49)
Maystadt et al. 2013#1997–2009SomaliaMonthProvinceTempCivil conflictYYY(66)
Miguel et al. 2004#‡‡1979–1999SSAAnnualCountryRainCivil warYYY(48)
O’Laughlin et al. 2012‡‖#1990–2009E. AfricaMonthPixel (1°)Rain/tempCivil/intergroupYYY(23)
Salehyan et al. 20121979–2006GlobalAnnualCountryPDSICivil/intergroupYYY(76)
Sarsons 20111970–1995IndiaAnnualMunicipalityRainIntergroupYYY(45)
Theisen et al. 2011‡#1960–2004AfricaAnnualPixel (0.5°)RainCivil conflictYNNN(24)
Theisen 2012‡‖#1989–2004KenyaAnnualPixel (0.25°)Rain/tempCivil/intergroupYYN**N (14)
Tol et al. 20091500–1900EuropeDecadeRegionRain/tempTransboundary YYY(60)
Zhang et al. 2007§§1400–1900N. Hem.CenturyRegionTempInstabilityYYY(59)
Institutional breakdown and population collapse (15)
Brückner et al. 2011#1980–2004SSAAnnualCountryRainInst. change YYY(78)
Buckley et al. 2010‖‖1030–2008CambodiaDecadeCountryDroughtCollapseN(85)
Büntgen et al. 2011‖‖400 BCE–2000EuropeDecadeRegionRain/tempInstabilityN(62)
Burke et al. 2010‡#1963–2007GlobalAnnualCountryRain/tempInst. changeYYY(77)
Cullen et al. 2000‖‖4000 BCE–0SyriaCenturyCountryDroughtCollapseN(83)
D’Anjou et al 2012550 BCE–1950NorwayCenturyMunicipalityTempCollapseYYY(89)
Ortloff et al. 1993‖‖500–2000PeruCenturyCountryDroughtCollapseN(80)
Haug et al. 2003‖‖0–1900MexicoCenturyCountryDroughtCollapseN(84)
Kelly et al. 201310050 BCE–1950USACenturyStateTemp/rainCollapseYYY(88)
Kennett et al. 201240 BCE–2006BelizeDecadeCountryRainCollapse N(87)
Kuper et al. 20068000–2000 BCEN. AfricaMillenniaRegionRainCollapse N(81)
Patterson et al. 2010200 BCE–1700IcelandDecadeCountryTempCollapseN(86)
Stahle et al. 19981200–2000USAMultiyearMunicipalityPDSICollapseN(82)
Yancheva et al. 2007‖‖2100 BCE–1700ChinaCenturyCountryRain/tempCollapseN(79)
Zhang et al. 20061000–1911ChinaDecadeCountryTempCivil conflict
and collapse
YYY(58)
Number of studies (60 total): 5047371
Fraction of those using statistical tests:100%94%74%2%

*Also see (33).

†Shown in Fig. 4.

‡Reanalyzed using the common statistical model containing location fixed effects and trends (see supplementary materials).

§Also see discussion in (32).

‖Shown in Fig. 2.

¶Actual experiment.

#Shown in Fig. 5.

**Effect size in the study is statistically significant at the 10% level, but not at the 5% level.

††Also see discussion in (22, 132137).

‡‡Also see discussion in (138, 139).

§§Also see (61).

‖‖Shown in Fig. 3.