LASSO合成控制法（LASSO synthetic control method）透過放寬合成控制法對權重與截距項的限制，提升預測反事實情境的準確性。本論文應用LASSO合成控制法，針對23個國家和當時的歐盟，評估其二氧化碳排放量受京都議定書影響的程度。由本文實證結果之個別年度觀察，發現多數國家沒有顯著減少二氧化碳排放量。觀察政策執行期間的平均結果，本文發現多數國家平均有減少碳排放量，但減量的程度沒有達統計上顯著，顯示京都議定書對各國在2005年到2012年二氧化碳排放量的影響，極為有限。

The LASSO synthetic control method relaxes restrictions on the weights and the intercept of the original synthetic control method so as to improve the prediction of counterfactual outcomes. We apply the LASSO synthetic control method to assess the Kyoto Protocol’s effect on CO2 emission reduction of 23 countries and the European Union, which consists of 15 member states at that time, with binding emission targets under the Kyoto Protocol. We cannot find the statistically significant negative treatment effect for most countries in the following years after the Kyoto Protocol entered into force. As for averaging yearly treatment effects for each country, we find that the average treatment effect for most countries is negative, but it is not statistically significant. In summary, we find little evidence for a significant CO2 emission reduction from 2005 to 2012 for most countries with binding emission targets under the Kyoto Protocol.

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