Well, this is unexpected. From the (conservative) Washington Examiner:
On Wednesday, the conservative American Enterprise Institute [AEI] hosted a secret meeting with other Washington, D.C., think tank officials, including members from several prominent liberal ones, to discuss how to build political support for a carbon pollution tax.
The discussion even apparently raised the subject of trying to get the upcoming post-election “lame duck” Congress to address the issue.
Representatives from such liberal groups as Union of Concerned Scientists, Public Citizen, the Center on Budget and Policy Priorities, and the Brookings Institute, the Climate Action Network and Clean, Air-Cool Planet joined centrist groups such as the Concord Coalition, Taxpayers for Common Sense, and the Joint Center for Political and Economic Studies and conservatives scholars from AEI and R Street, a group that broke away from the Heartland Institute.
"Liberal groups" like the Union of Concerned Scientists. Got it.