BATON ROUGE, June 13 -- The Louisiana parishes that have spent the past decade suing oil and gas companies over coastal erosion just won a permanent exemption from the law their own governor signed Thursday to stop suits like theirs. That is the strange shape of HB 804, the Louisiana Energy Protection Act, the bill the Pelican State has chosen as its closing argument in the national fight over whether climate science belongs in a courtroom.

Governor Jeff Landry signed the measure into law, closing the door, he said, to frivolous litigation. The law bars civil lawsuits in Louisiana state court that seek damages for personal injury, property loss or economic harm explicitly tied to greenhouse gas emissions and global climate change. In sig...