The Senate’s point person on climate change legislation said he doesn’t know where Gov. Charlie Baker came up with his estimate that the Legislature’s target for emissions reductions in 2030 would cost state residents an extra $6 billion.

 “Boy would I like to know,” said Sen. Michael Barrett of Lexington. “I have never – and I am familiar with all of the written documents the administration has released on this topic – I had never seen that $6 billion figure until [Thursday]. I wonder if the governor had ever seen the $6 billion figure until [Thursday].”

 In his letter vetoing the Legislature’s climate change bill, Baker said the difference between a 45 percent reduction in emissions by 2030 compared to 1990 levels versus a 50 percent reduction was $6 billion in extra costs incurred by Massachusetts residents. “Unfortunately, this higher cost does not materially increase the Commonwealth’s ability to achieve its long-term climate goals,” the letter said.

 A spokesman for the Baker administration wasn’t able to produce the analysis yielding the $6 billion figure on Friday but promised more information this week.

 Barrett, appearing on The Codcast with Bradley Campbell, the president of the Conservation Law Foundation, said he has asked repeatedly for information on the $6 billion figure and never received it. 

 “I can’t wait to see the economic study that buttresses that claim because it will be unlike any economic study I’ve ever read,” he said. “These figures to some extent are arbitrary. Neither figure [45 percent or 50 percent] is supported by modeling. Both are judgment calls.” 

Campbell said the governor’s reputation for addressing climate change will take a hit because of his veto of the Legislature’s bill. He said trying to estimate the future costs of addressing climate change is difficult and estimates are typically way too high. He said Baker’s veto wastes valuable time and suggests the governor still believes addressing climate change comes at the expense of the economy.

 As for the governor’s veto letter, Campbell said he was not convinced. “It really was a cobbled-together collection of politically tinged arguments rather than substantive objections that the Legislature could have addressed,” he said. “In some cases, they were objections the Legislature did address.”

 Barrett felt similarly. “I assume the governor didn’t write it himself, that it was a staff workup,” he said. “I could not extract from it a coherent, well-constructed case against anything currently in the Senate bill.”