(CNN) Acting EPA Administrator Andrew Wheeler has appointed five new members of an independent committee that provides advice to the EPA on national air quality standards, replacing the current members, while reducing the amount of support it gets from other scientists, according to an agency statement and emails obtained by CNN.

Wheeler's appointments mean that the Clean Air Scientific Advisory Committee's (CASAC) entire membership has been replaced over the course of the year.

The changes have left some scientists concerned that the committee will not be able to properly advise the EPA on its policies and procedures regarding national air quality standards.

"Protecting the public's health from dangerous amounts of pollutants in the air that we all breathe is the mandate of this agency," Jack Harkema, a professor of pathobiology and diagnostic investigation at Michigan State University and now-former member of the committee, told CNN. "This cannot be done without careful, deliberate and knowledgeable understanding [of] this complex environmental health issue. Multidisciplinary teams of scientific experts must be free to conduct thorough peer-review of the pertinent science. Millions of lives are at stake."

During an interview with CBS's "60 Minutes" on Sunday, President Donald Trump expressed skepticism that climate change was a man-made problem, stating "I think something's happening. Something's changing ... I think there's probably a difference. But I don't know that it's man-made."

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