Mark Liang (J.D. 2010, Chicago) has published Comment, Green Taxes and the WTO: Creating Certainty for the Future, 10 Chi. J. Int'l L. 359 (2009).  Here is the Conclusion:

The WTO's existing jurisprudence indicates no clear guidelines or per se rules on whether internal taxes that are facially neutral, but potentially discriminatory in effect, violate Article III:2 of the GATT. The confusion over Article III:2's treatment of such taxes is problematic. In coming years, it is anticipated that many WTO countries will promulgate green taxes as a means of improving environmental protections and encouraging energy conservation. Many of these green taxes could disproportionately affect imports relative to domestically produced goods. If the WTO finds that many green taxes do violate Article III:2, this may place an undue and burdensome limitation on nations' autonomy to pursue legitimate domestic objectives of environmental protection and energy conservation. However, if the WTO establishes a per se rule that all facially neutral green taxes comply with Article III:2, member states may couch protectionist tax measures as environmentally motivated.

This Comment proposed a framework for the WTO to use in adjudicating future disputes concerning green taxes. Section II fleshed out relevant considerations the WTO will employ in determining a tax's compliance with Article III:2. Section III examined the WTO's jurisprudence on Article XX. Section IV presented the precautionary principle and its implications for future green tax disputes. Section V merged the previous three sections and proposed the test the WTO Dispute Body will likely employ in adjudicating future green tax disputes.

Section VI applied the proposed test from Section V to a hypothetical dispute concerning China's recently announced engine size tax. The specific finding of Section VI was that the WTO should find that the engine size tax violates Article III:2 but should grant an Article XX(g) exemption due to its expected effectiveness in combating recognized environmental risks, including poor air quality and global warming. The broader conclusion of Section VI and this Comment was that green taxes should be upheld in future WTO disputes. The WTO is an international organization sensitive to modern policy concerns and the shared needs of its member states. The WTO's recent jurisprudence and adoption of the precautionary principle signal the WTO's willingness to accommodate national policies addressing environmental and conservation concerns. The WTO is unlikely to intrude into member nation's autonomy when their policies address these legitimate policy goals.