¹ Axelrod, Robert, The Complexity of Cooperation: Agent-based Models of Competition and Collaboration (Princeton, N.J.: Princeton University Press, 1997)Google Scholar; Keohane, Robert and Nye, Joseph, Power and Interdependence (Boston, Mass.: Little, Brown, 1977)Google Scholar.

² Hafner-Burton, Emilie M., von Stein, Jana and Gartzke, Erik, ‘International Organizations Count’, Journal of Conflict Resolution, 52 (2008), 175–188CrossRefGoogle Scholar.

³ Jahn, Detlef, ‘Globalization as “Galton’s Problem”: The Missing Link in the Analysis of Diffusion Patterns in Welfare State Development’, International Organization, 60 (2006), 401–431CrossRefGoogle Scholar. In 1889, Sir Francis Galton argued that cultural similarities could be due not only to evolutionary development but also to common descent and borrowing. He also argued that explanations that did not take into account all these possibilities could arrive at false conclusions. In our case, these driving forces can be conceptualized in terms of country-internal characteristics and country-external factors.

⁴ Mitchell, Ronald B., ‘International Environment’, in Thomas Risse, Beth Simmons and Walter Carlsnaes, eds, Handbook of International Relations (London: Sage, 2002), pp. 500–516CrossRefGoogle Scholar.

⁵ Haas, Peter M., Keohane, Robert O. and Levy, Marc A., Institutions for the Earth: Sources of Effective International Environmental Protection (Cambridge, Mass.: MIT Press, 1993)Google Scholar; Bernauer, Thomas, ‘The Effect of International Environmental Institutions: How We Might Learn More’, International Organization, 49 (1995), 351–377CrossRefGoogle Scholar; Siegfried, Tobias and Bernauer, Thomas, ‘Estimating the Performance of International Regulatory Regimes: Methodology and Empirical Application to International Water Management in the Naryn / Syr Darya Basin’, Water Resources Research, 43 (2007), 1–14CrossRefGoogle Scholar; Young, Oran, The Effectiveness of International Environmental Regimes: Causal Connections and Behavioral Mechanisms (Global Environmental Accord: Strategies for Sustainability and Institutional Innovation), (Cambridge, Mass.: MIT Press, 1999)Google Scholar; Helm, Carsten and Sprinz, Detlef, ‘Measuring the Effectiveness of International Environmental Regimes’, Journal of Conflict Resolution, 44 (2000), 630–652CrossRefGoogle Scholar; Mitchell, Ronald B., ‘Regime Design Matters: Intentional Oil Pollution and Treaty Compliance’, International Organization, 48 (1994), 425–458CrossRefGoogle Scholar.

⁶ Frank, David J., ‘The Social Bases of Environmental Treaty Ratification, 1900–1990’, Sociological Inquiry, 69 (1999), 523–550CrossRefGoogle Scholar. Neumayer, Eric, ‘Does Trade Openness Promote Multilateral Environmental Cooperation?’ World Economy, 25 (2002), 815–832CrossRefGoogle Scholar; Neumayer, Eric, ‘Do Democracies Exhibit Stronger International Environmental Commitment? A Cross-Country Analysis’, Journal of Peace Research, 39 (2002), 139–164CrossRefGoogle Scholar; Murdoch, James C., Sandler, Todd and Vijverberg, Wim P.M., ‘The Participation Decision versus the Level of Participation in an Environmental Treaty: A Spatial Probit Analysis’, Journal of Public Economics, 87 (2003), 337–362CrossRefGoogle Scholar; Roberts, Timmons J., Parks, Bradley C. and Vásquez, Alexis A., ‘Who Ratifies Environmental Treaties and Why? Institutionalism, Structuralism and Participation by 192 Nations in 22 Treaties’, Global Environmental Politics, 4 (2004), 22–64CrossRefGoogle Scholar; von Stein, Jana, ‘The International Law and Politics of Climate Change’, Journal of Conflict Resolution, 52 (2008), 243–268CrossRefGoogle Scholar.

⁷ Von Stein, , ‘The International Law and Politics of Climate Change’, p. 243Google Scholar.

⁸ Murdoch, et al. , ‘The Participation Decision versus the Level of Participation in an Environmental Treaty’Google Scholar.

⁹ Neumayer, , ‘Does Trade Openness Promote Multilateral Environmental Cooperation?’Google Scholar

¹⁰ Neumayer, , ‘Do Democracies Exhibit Stronger International Environmental Commitment?’Google Scholar

¹¹ Neumayer, , ‘Do Democracies Exhibit Stronger International Environmental Commitment?’ p. 139Google Scholar.

¹² Congleton, Roger D., ‘Political Institutions and Pollution Control’, Review of Economics and Statistics, 74 (1992), 412–421CrossRefGoogle Scholar; Fredriksson, Per G. and Noel Gaston, ‘Ratification of the 1992 Climate Change Convention: What Determines Legislative Delay?’, Public Choice, 104 (2000), 345–368CrossRefGoogle Scholar.

¹³ Fredriksson, Per G. and Ujhelyi, Gergely, ‘Political Institutions, Interest groups, and the Ratification of International Environmental Agreements’ (Houston, Texas: University of Houston, Department of Economics Working Paper, 2006)Google Scholar.

¹⁴ Murdoch, et al. , ‘The Participation Decision versus the Level of Participation in an Environmental Treaty’Google Scholar.

¹⁵ Zilbauer, Matthias, ‘Determinants of International Environmental Cooperation: Does ENDO Strength Foster a Country’s International Environmental Commitment?’ (unpublished manuscript, Konstanz: University of Konstanz, 2005)Google Scholar.

¹⁶ Zilbauer, , ‘Determinants of International Environmental Cooperation’, p. 5Google Scholar.

¹⁷ Roberts, et al. , ‘Who Ratifies Environmental Treaties and Why?’Google Scholar

¹⁸ Roberts, et al. , ‘Who Ratifies Environmental Treaties and Why?’ p. 39Google Scholar.

¹⁹ Frank, , ‘The Social Bases of Environmental Treaty Ratification, 1900–1990’Google Scholar.

²⁰ Frank, , ‘The Social Bases of Environmental Treaty Ratification, 1900–1990’Google Scholar; Roberts, et al. , ‘Who Ratifies Environmental Treaties and Why?’Google Scholar

²¹ Von Stein, , ‘The International Law and Politics of Climate Change’; Zilbauer, ‘Determinants of International Environmental Cooperation’Google Scholar.

²² Detlef Jahn, ‘The Politics of Climate Change’ (paper presented at the ECPR conference, 2008, Rennes; Simmons, Beth A., Dobbin, Frank and Garrett, Geoffrey, ‘Introduction: The International Diffusion of Liberalism’, International Organization, 60 (2006), 781–810CrossRefGoogle Scholar; Simmons, Beth A. and Zachary Elkins, ‘The Globalization of Liberalization: Policy Diffusion in the International Political Economy’, American Political Science Review, 98 (2004), 171–189CrossRefGoogle Scholar; Ward, Hugh, ‘International Linkages and Environmental Sustainability: The Effectiveness of the Regime Network’, Journal of Peace Research, 43 (2006), 149–166CrossRefGoogle Scholar.

²³ Carter, David B. and Signorino, Curtis S., ‘Back to the Future: Modeling Time Dependence with Binary Data’ (Working Paper, University of Rochester, Department of Political Science, 2009)Google Scholar.

²⁴ Drezner, Daniel, ‘Globalizers of the World, Unite!’, Washington Quarterly, 21 (1998), 207–225CrossRefGoogle Scholar; Sachs, Jeffrey, ‘International Economics: Unlocking the Mysteries of Globalization’, Foreign Policy, 110 (1998), 97–111CrossRefGoogle Scholar.

²⁵ Pevehouse, Jon C., Nordstrom, Timothy and Warnke, Kevin, ‘The COW-2 International Organizations Dataset Version 2.0’, Conflict Management and Peace Science, 21 (2004), 101–119CrossRefGoogle Scholar.

²⁶ Aust, Anthony, Modern Treaty Law and Practice (Cambridge: Cambridge University Press, 2000)Google Scholar.

²⁷ Keohane, Robert, After Hegemony: Cooperation and Discord in the World Political Economy (Princeton, N.J.: Princeton University Press, 1984)Google Scholar.

²⁸ Keohane, , After HegemonyGoogle Scholar; Haas, et al. , Institutions for the EarthGoogle Scholar; Mitchell, , ‘Regime Design Matters’Google Scholar; Abbott, Kenneth W. and Duncan Snidal, ‘Why States Act through Formal International Organizations’, Journal of Conflict Resolution, 42 (1998), 3–32CrossRefGoogle Scholar.

²⁹ Young, Oran, International Governance: Protecting the Environment in a Stateless Society (Ithaca, N.Y.: Cornell University Press, 1994)Google Scholar; Young, , The Effectiveness of International Environmental Regimes.Google Scholar

³⁰ Meyer, John W., Frank, David J., Hironaka, Ann, Schofer, Evan and Brandon Tuma, Nancy, ‘The Structuring of a World Environmental Regime, 1870–1990’, International Organization, 51 (1997), 623–651CrossRefGoogle Scholar.

³¹ Boehmer, Charles, Gartzke, Erik and Nordstrom, Timothy, ‘Do International Organizations Promote Peace?’ World Politics, 57 (2004), 1–38CrossRefGoogle Scholar.

³² Mitrany, David, A Working Peace System (Chicago: Quadrangle, 1966)Google Scholar; Haas, Ernst, Beyond the Nation-State (Palo Alto, Calif.: Stanford University Press, 1964)Google Scholar.

³³ Axelrod, and Keohane, , ‘Achieving Cooperation under Anarchy’, p. 250, state that ‘International regimes do not substitute for reciprocity; rather they reinforce and institutionalize it, … delegitimizing defection and thereby making it more costly’Google Scholar.

³⁴ Simmons, Beth A., ‘Credibility, Costs, and Institutions: Cooperation on Economic Sanctions’, World Politics, 45 (1993), 406–432Google Scholar; Mercer, Jonathan, Reputation and International Politics (Ithaca, N.Y.: Cornell University Press, 1996)Google Scholar.

³⁵ Simmons, , ‘Credibility, Costs, and Institutions’Google Scholar.

³⁶ Ruoff, Gabriele, ‘Grow Rich and Clean Up Later? Joint Effects of International Integration and Democracy on Environmental Quality in Developing Countries’ (doctoral dissertation, CIS, ETH Zurich, 2009)Google Scholar; Jorgenson, Andrew K., ‘Foreign Direct Investment and the Environment, the Mitigating Influence of Institutional and Civil Society Factors, and Relationships between Industrial Pollution and Human Health: A Panel Study of Less-Developed countries’, Organization and Environment, 22 (2009), 135–157CrossRefGoogle Scholar; Jorgenson, Andrew K., ‘Political-Economic Integration, Industrial Pollution and Human Health: A Panel Study of Less-Developed Countries, 1980–2000’, International Sociology, 24 (2009), 115–143CrossRefGoogle Scholar.

³⁷ We are aware that international economic integration is not limited to international trade, and that capital and labour mobility might be as important; but we leave their analysis to future research.

³⁸ Neumayer, , ‘Does Trade Openness Promote Multilateral Environmental Cooperation?’Google Scholar

³⁹ Neumayer, , ‘Does Trade Openness Promote Multilateral Environmental Cooperation?’ p. 831Google Scholar.

⁴⁰ Prakash, Aseem and Potoski, Matthew, ‘Racing to the Bottom? Trade, Environmental Governance, and Iso 14001’, American Journal of Political Science, 50 (2006), 350–364CrossRefGoogle Scholar.

⁴¹ Prakash, and Potoski, , ‘Racing to the Bottom?’ p. 350Google Scholar.

⁴² Beron, Kurt J., Murdoch, James C. and Wim P.M. Vijverberg, ‘Why Cooperate? Public Goods, Economic Power, and the Montreal Protocol’, Review of Economics and Statistics, 85 (2003), 286–297CrossRefGoogle Scholar; Wagner, Ulrich J., ‘Estimating Strategic Complementarities in a Dynamic Game of Timing: The Case of the Montreal Protocol’ (Working Paper, The Earth Institute, Columbia University, 2008)Google Scholar.

⁴³ Oneal, John R. and Bruce Russett, ‘Assessing the Liberal Peace with Alternative Specifications: Trade Still Reduces Conflict’, Journal of Peace Research, 36 (1999), 423–442CrossRefGoogle Scholar; Gartzke, Erik, ‘The Capitalist Peace’, American Journal of Political Science, 51 (2008), 166–191CrossRefGoogle Scholar; Barbieri, Katherine, The Liberal Illusion: Does Trade Promote Peace? (Ann Arbor: University of Michigan Press, 2002)CrossRefGoogle Scholar, however, finds that more trade leads to more conflict. See Schneider, Gerald, Barbieri, Katherine and Petter Gleditsch, Nils, eds, Globalization and Armed Conflict (Lanham, Md.: Rowman and Littlefield, 2003)Google Scholar, for a survey of the literature.

⁴⁴ Vogel, David, ‘Trading up and Governing Across: Transnational Governance and Environmental Protection’, Journal of European Public Policy, 4 (1997), 556–571CrossRefGoogle Scholar.

⁴⁵ Bernauer, Thomas and Caduff, Ladina, ‘In Whose Interest? Pressure Group Politics, Economic Competition and Environmental Regulation’, Journal of Public Policy, 24 (2004), 99–126CrossRefGoogle Scholar.

⁴⁶ Simmons, et al. , ‘Introduction: The International Diffusion of Liberalism’Google Scholar.

⁴⁷ Elkins, Zachary, Guzman, Andrew and Simmons, Beth, ‘Competing for Capital: The Diffusion of Bilateral Investment Treaties, 1960–2000’, International Organization, 60 (2006), 811–846CrossRefGoogle Scholar; Simmons, et al. , ‘Introduction: The International Diffusion of Liberalism’Google Scholar; Meseguer, Covadonga, ‘Policy Learning, Policy Diffusion and the Making of a New Order’, Annals of the American Academy of Political and Social Sciences, 598 (2005), 67–82CrossRefGoogle Scholar; Meseguer, Covadonga, ‘Learning and Economic Policy Choices’, European Journal of Political Economy, 22 (2006), 156–178CrossRefGoogle Scholar; Levi-Faur, David, ‘The Global Diffusion of Regulatory Capitalism’, Annals of the American Academy of Political and Social Sciences, 598 (2005), 12–33CrossRefGoogle Scholar; Elkins, Zachary and Simmons, Beth, ‘On Waves, Clusters, and Diffusion: A Conceptual Framework’, Annals of the American Academy of Political and Social Sciences, 598 (2005), 33–51CrossRefGoogle Scholar; Henisz, Witold J., Zelner, Bennet A. and Guillén, Mauro F., ‘International Coercion, Emulation and Policy Diffusion: Market-Oriented Infrastructure Reforms, 1977–1999’, American Sociological Review, 70 (2005), 871–897CrossRefGoogle Scholar; Simmons, and Elkins, , ‘The Globalization of Liberalization’Google Scholar.

⁴⁸ Simmons, , Dobbin, and Garrett, , ‘Introduction: The International Diffusion of Liberalism’, p. 787Google Scholar.

⁴⁹ Elkins, et al. , ‘Competing for Capital’Google Scholar.

⁵⁰ Simmons, and Elkins, , ‘The Globalization of Liberalization’Google Scholar.

⁵¹ Henisz, et al. , ‘International Coercion, Emulation and Policy Diffusion’Google Scholar.

⁵² Article VIII prohibits restrictions on a country’s current account ( Simmons, Beth A., ‘International Law and State Behavior: Commitment and Compliance in International Monetary Affairs’, American Political Science Review, 94 (2000), 819–836CrossRefGoogle Scholar, p. 820).

⁵³ Simmons, , ‘International Law and State Behavior’Google Scholar.

⁵⁴ Selden, Thomas M. and Song, Daqing, ‘Environmental Quality and Development: Is there a Kuznets Curve for Air Pollution Emissions?’ Journal of Environmental Economics and Management, 27 (1994), 147–162CrossRefGoogle Scholar; Grossman, Gene M. and Krueger, Alan B., ‘Economic Growth and the Environment’, Quarterly Journal of Economics, 110 (1995), 353–377CrossRefGoogle Scholar.

⁵⁵ Fearon, James D., ‘Domestic Political Audience and the Escalation of International Disputes’, American Political Science Review, 88 (1994), 577–592CrossRefGoogle Scholar; Taylor Gaubatz, Kurt, ‘Democratic States and Commitment in International Relations’, International Organization, 50 (1996), 109–139CrossRefGoogle Scholar; Ashley Leeds, Brett, ‘Domestic Political Institutions, Credible Commitments, and International Cooperation’, American Journal of Political Science, 43 (1999), 979–1002CrossRefGoogle Scholar; Martin, Lisa, Democratic Commitments: Legislatures an International Cooperation (Princeton, N.J.: Princeton University Press, 2000)CrossRefGoogle Scholar; Mansfield, Edward D., Milner, Helen V. and Rosendorff, Peter B., ‘Why Democracies Cooperate More: Electoral Control and International Trade Agreements’, International Organization, 56 (2002), 477–513CrossRefGoogle Scholar.

⁵⁶ Kalbhenn, Anna, ‘A River Runs Through It: Democracy, International Interlinkages and Cooperation over Shared Resources’ (NCCR Working Paper No. 32, 2009)Google Scholar, for example, shows that democratic pairs of countries tend to co-operate more in international river management issues than non-democratic or mixed dyads. See also Bernauer, Thomas and Kuhn, Patick, ‘Is There an Environmental Version of the Kantian Peace? Insights From Water Pollution in Europe’, European Journal of International Relations, 16 (2010), 77–102CrossRefGoogle Scholar.

⁵⁷ Baettig, Michèle B. and Thomas Bernauer, ‘National Institutions and Global Public Goods: Are Democracies More Cooperative in Climate Change Policy?’ International Organization, 63 (2009), 281–308CrossRefGoogle Scholar.

⁵⁸ Payne, Rodger A., ‘Freedom and the Environment’, Journal of Democracy, 6 (1995), 41–55CrossRefGoogle Scholar.

⁵⁹ Slantchev, Branislav L., ‘Politicians, the Media, and Domestic Audience Costs’, International Studies Quarterly, 50 (2006), 445–477CrossRefGoogle Scholar.

⁶⁰ For example, Congleton, ‘Political Institutions and Pollution Control’; Olson, Mancur, ‘Dictatorship, Democracy and Development’, American Political Science Review, 87 (1993), 567–576CrossRefGoogle Scholar; McGuire, Martin and Olson, Mancur, ‘The Economics of Autocracy and Majority Rule: The Invisible Hand and the Use of Force’, Journal of Economic Literature, 34 (1996), 72–96Google Scholar; Niskanen, William, ‘Autocratic, Democratic and Optimal Government’, Economic Inquiry, 35 (1997), 464–479CrossRefGoogle Scholar; Lake, David and Baum, Matthew, ‘The Invisible Hand of Democracy: Political Control and the Provision of Public Service’, Comparative Political Studies, 34 (2001), 587–621CrossRefGoogle Scholar; Bruce Bueno de Mesquita, Alastair Smith, Siverson, Randolph M. and Morrow, James D., The Logic of Political Survival (Cambridge, Mass.: MIT Press, 2003)Google Scholar; Bernauer, Thomas and Koubi, Vally, ‘Effects of Political Institutions on Air Quality’, Ecological Economics, 68 (2009), 1355–1365CrossRefGoogle Scholar.

⁶¹ Bernauer, and Koubi, , ‘Effects of Political Institutions on Air Quality’Google Scholar.

⁶² Congleton, , ‘Political Institutions and Pollution Control’Google Scholar.

⁶³ Bueno de Mesquita et al., The Logic of Political Survival, empirically show that once autocratic leaders have succeeded in surviving in office during the initial years of seizing power, then they survive in office longer than their democratic counterparts (chap. 7).

⁶⁴ See, for example, Neumayer, , ‘Do Democracies Exhibit Stronger International Environmental Commitment?’; Zilbauer, ‘Determinants of International Environmental Cooperation’; Von Stein, ‘The International Law and Politics of Climate Change’; Bernauer and Koubi, ‘Effects of Political Institutions on Air Quality’; Baettig and Bernauer, ‘National Institutions and Global Public Goods: Are Democracies More Cooperative in Climate Change Policy?’Google Scholar

⁶⁵ Neumayer, , ‘Do Democracies Exhibit Stronger International Environmental Commitment?’ p. 150Google Scholar.

⁶⁶ The failure of the United States to ratify the Kyoto Protocol is a good example.

⁶⁷ Sprinz, Detlef and Vaahtoranta, Tapani, ‘The Interest-Based Explanation of International Environmental Policy’, International Organization, 48 (1994), 77–105CrossRefGoogle Scholar, p. 79.

⁶⁸ In this article, we use the term ‘ratification’ to indicate any form of binding commitment (as opposed to signature). Depending on the specific legal context, this commitment can also be expressed by adhesion, accession, etc.

⁶⁹ CIESIN, ‘Environmental Treaties and Resource Indicators (ENTRI)’ (2006), available at: http://sedac.ciesin.columbia.edu/entri/, accessed 13 December 2006Google Scholar; Mitchell, Ronald B., ‘International Environmental Agreements Database Project’ (2002–08), Version 2007.1, available at: http://iea.uoregon.edu/, accessed 18 March 2008Google Scholar.

⁷⁰ The number of treaties that has been ratified by a country varies between 132 in the case of France or 126 in the case of Great Britain and nine in the case of Somalia or only eight in the case of Bhutan.

⁷¹ Pevehouse, et al. , ‘The COW-2 International Organizations Dataset Version 2.0’Google Scholar.

⁷² The data are taken from Skrede Gleditsch, Kristian, ‘Expanded Trade and GDP Data’, Journal of Conflict Resolution, 46 (2002), 712–724CrossRefGoogle Scholar; and Heston, Alan, Summers, Robert and Aten, Bettina, ‘Penn World Table Version 6.2’ (Center for International Comparisons of Production, Income and Prices at the University of Pennsylvania, 2006)Google Scholar.

⁷³ See http://www.iiasa.ac.at/Research/POP/proj01/countries.html. The regions are: Centrally Planned Asia, Central Asia, North Africa, Middle East, Sub-Saharan Africa, Latin America, Western Europe, Eastern Europe, North America, Pacific OECD, South Asia, Former Soviet Union, Pacific Asia.

⁷⁴ These data are taken from Gleditsch, , ‘Expanded Trade and GDP Data’Google Scholar.

⁷⁵ House, Freedom, ‘Methodology’, see the website, http://www.freedomhouse.org/template.cfm?page=351&ana_page=341&year=2008, accessed 2 November 2009Google Scholar.

⁷⁶ Jaggers, Keith and Gurr, Ted R., ‘Tracking Democracy’s Third Wave with the Polity III Data’, Journal of Peace Research, 32 (1995), 469–482CrossRefGoogle Scholar; Marshall, Monty G. and Jaggers, Keith, ‘Polity IV Project: Political Regime Characteristics and Transitions, 1800–2002’, Dataset Users’s Manual (Polity IV, 2002)Google Scholar.

⁷⁷ Vanhanen, Tatu, ‘A New Dataset for Measuring Democracy, 1810–1998’, Journal of Peace Research, 37 (2000), 251–265CrossRefGoogle Scholar. The political rights element of the Freedom House Index, which is very close to the Polity IV measure of democracy, captures mainly the fairness and freedom of elections, that is, whether a government came to power by election or by non-democratic means; whether elections, if any, are free and fair; and whether an opposition exists and has the opportunity to take power with the consent of the electorate.

⁷⁸ Singer, David J., Bremer, Stuart and Stuckey, John, ‘Capability Distribution, Uncertainty, and Major Power War, 1820–1965’, in Bruce Russet, ed., Peace, War, and Numbers (Beverly Hills, Calif.: Sage, 1972), pp. 19–48Google Scholar.

⁷⁹ Gleditsch, , ‘Expanded Trade and GDP Data’Google Scholar.

⁸⁰ Stern, David I., ‘Global Sulfur Emissions From 1850 to 2000’, Chemosphere, 58 (2005), 163–175CrossRefGoogle Scholar.

⁸¹ We have used a more differentiated definition of regions to assess contingency effects (see above). The regional dummies are defined in broader terms because their main goal is to control for any remaining effects on treaty ratification that may emanate from a less clearly defined set of geographic or ecological factors.

⁸² Only in very rare circumstances does a country withdraw from a treaty it has already ratified. If this was the case, the particular country–treaty combination was reintegrated into the dataset.

⁸³ Carter, and Signorino, , ‘Back to the Future’Google Scholar.

⁸⁴ Beck, Nathaniel, Katz, Jonathan N. and Tucker, Richard, ‘Taking Time Seriously: Time-Series-Cross-Section Analysis with a Binary Dependent Variable’, American Journal of Political Science, 42 (1998), 1260–1288CrossRefGoogle Scholar.

⁸⁵ In addition to the inclusion of t, t ² and t ³, we test the robustness of our results by including time dummies and decade dummies. The decade dummies are a possibility to control for changing environmental consciousness over time and thus constitute an additional approach to dealing with time dependence in our model. The corresponding results can be found in the web appendix.

⁸⁶ Beck, et al. , ‘Taking Time Seriously’Google Scholar.

⁸⁷ Carter, and Signorino, , ‘Back to the Future’Google Scholar.

⁸⁸ All models were estimated using robust standard errors clustered by countries to control for the fact that observations for the same country may be more similar than observations across different countries.

⁸⁹ A more intuitive illustration is provided in the web appendix by a similar figure using GDP per capita instead of the log of GDP per capita.

⁹⁰ Although political rights and civil liberties, as measured by Freedom House, are highly correlated, they capture distinct phenomena. For example, some countries score lower on civil rights than on political rights (e.g. Italy, Argentina and Colombia) and others score higher on civil liberties than on political rights (e.g. Peru and Brazil). In any event, high correlation between the two variables does not cast doubt on our findings because multicollinearity does not bias coefficients. It only increases standard errors, which make it harder to obtain statistically significant results.

⁹¹ See, for example, Roberts, et al. , ‘Who Ratifies Environmental Treaties and Why?’ Frank, ‘The Social Bases of Environmental Treaty Ratification, 1900–1990’Google Scholar.

⁹² We also tested the effect of ratification by important countries with a dummy variable indicating whether the particular country is a major power (based on the Correlates of War data). This variable has no significant effects in our models – see web appendix.

⁹³ Using a likelihood ratio test, we examined whether there is time dependence in our model. The test clearly rejected the model without t, t ², t ³ (LR chi²(3) = 7977.55; Prob > chi² = 0.00).

⁹⁴ The simulation results were obtained using CLARIFY ( Tomz, Michael, Wittenberg, Jason and King, Gary, ‘CLARIFY: Software for Interpreting and Presenting Statistical Results’, Version 2.0 (Cambridge, Mass.: Harvard University, 1 June 2001), see http://gking.harvard.eduGoogle Scholar; King, Gary, Tomz, Michael and Wittenberg, Jason, ‘Making the Most of Statistical Analyses: Improving Interpretation and Presentation’, American Journal of Political Science, 44 (2000), 347–361CrossRefGoogle Scholar).

⁹⁵ To further illustrate the effects of our main independent variables, we have created graphs that plot the likelihood of treaty ratification over the whole range of the independent variable in question while all other variables are kept at their mean values. These figures can be found in the web appendix.

⁹⁶ Since we include both GDP per capita and its square as terms in the regression, we use Figure 1 to illustrate the overall effect of GDP per capita on treaty ratification. From this figure, we can deduce that the change in probabilities from the minimum to the maximum level of GDP per capita is smaller than for the contingent behaviour variables such as the number of other countries that have ratified the treaty.

⁹⁷ Ward, ‘International Linkages and Environmental Sustainability’; Braun, Dietmar and Gilardi, Fabrizio, ‘Taking “Galton's Problem” Seriously’, Journal of Theoretical Politics, 18 (2006), 298–322CrossRefGoogle Scholar; Dorussen, Han and Ward, Hugh, ‘Intergovernmental Organizations and the Kantian Peace: A Network Perspective’, Journal of Conflict Resolution, 52 (2008), 189–212CrossRefGoogle Scholar; Shipan, Charles and Volden, Craig, ‘The Mechanisms of Policy Diffusion’, American Journal of Political Science, 52 (2008), 840–857CrossRefGoogle Scholar.

⁹⁸ Ward, , ‘International Linkages and Environmental Sustainability’Google Scholar.