Science envoy resigns over Trump's Charlottesville comments

He was one of seven science envoys now working with the State Department.

In his letter, Kammen included an acrostic, in which the first letter of each paragraph spelled out IMPEACH. This is a move similar to the resignation letter from members of the President’s Committee on the Arts and Humanities, who spelled out RESIST.

"Today, Dr. Daniel Kammen made a personal decision to resign. We appreciate his dedicated service to U.S. scientific diplomacy during his appointment working on energy efficiency and renewable energy in Africa as a Science Envoy," a State Department official told ABC News.

Kammen was not the State Department's science envoy, but one of three unpaid scientists and engineers who have been working with the agency on key scientific issues. Science envoys are different than the special envoy roles filled by full-time employees at the State Department, in that they work with the agency to foster cooperation with foreign governments, businesses, universities and others.

Since 2010, 18 science envoys have worked with the State Department and visited 41 countries, according to a State Department official. Their terms last about one year.