The Trump administration has begun firing employees at the National Oceanic and Atmospheric Administration, one of the world’s premier centers for climate science.

The firings are expected to cost more than 800 people their jobs, out of a total of about 13,000 staff members, according to two people familiar with the situation who declined to be identified for fear of retribution. The notifications went out on Thursday afternoon.

A policy analyst at the National Ocean Service, a NOAA agency office near Washington, described a scramble as supervisors frantically tried to help probationary employees download relevant documents like pay slips and performance reviews before they lost access to computers.

“This loss of talent at NOAA is going to set the agency back years and compromise the integrity of missions that directly support human health and safety, economic prosperity and national security,” the analyst said, speaking on the condition of anonymity for fear of retribution. “This is not a move toward efficiency; it’s a move toward putting Americans in danger every day.”

The firings are focused on probationary employees, who have been in their jobs for a short period and lack the protections afforded to staff members with longer tenure. As is the case at other agencies, the Trump administration appears to be firing probationary employees at NOAA not because their work is necessarily less valuable than that of other staff members, but because they’re easier to dismiss.

NOAA is part of the Commerce Department. Cuts had been delayed at NOAA and other parts of the department until the new secretary, Howard Lutnick, could come into office. But since Mr. Lutnick was sworn in on Monday, more layoffs have started to be announced throughout the department, including at the International Trade Administration, which promotes U.S. exports.