Sen. David Vitter (R-La.) says something’s missing in the revised White House estimate of economic damages from carbon emissions: proper names.

Vitter pressed a senior Environmental Protection Agency (EPA) official Tuesday for names of participants in the interagency process to revise the “social cost of carbon,” a metric of carbon pollution’s toll.

“To anyone outside the administration including me, this is like a black box,” Vitter, the top Republican on the Senate Environment and Public Works Committee, told EPA’s Sarah Durham at a hearing Tuesday.

“We have been asking a number of legitimate questions through at least two letters about that process and about the participants, and I have just gotten no information yet,” he told Durham, head of EPA’s Office of Atmospheric Programs.

Vitter and some other Republicans, as well as major business groups, say May’s upward revision of the social cost of carbon, a metric used to weigh the benefits of carbon-cutting regulations, was not done transparently.