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WASHINGTON — The Senate will not vote this year to confirm a new head of the National Oceanic and Atmospheric Administration, lawmakers said this week. That leaves the agency responsible for understanding and predicting changes in the earth’s climate without a Senate-confirmed leader for the longest period since it was created in 1970 .

Barry Lee Myers, the chief executive of AccuWeather, a private forecasting firm that relies largely on data from the agency’s National Weather Service, has been a controversial figure since President Trump first nominated him to lead the agency in October 2017. Democrats have said that Mr. Myers has significant conflicts of interest, including his past eagerness to privatize the National Weather Service . For several years, Mr. Myers fought government programs that would compete with AccuWeather services.

Senator Bill Nelson of Florida, the top Democrat on the Commerce Committee, which oversees the agency, said a vote on Mr. Myers was not in the cards before Congress leaves at the end of the year.

“I think that things are so crunched it’s going to be very difficult to get that,” Mr. Nelson said.

Republicans blamed Democrats for the delay. Mr. Trump had to renominate Mr. Myers in January after the Senate failed to act last year. Mr. Myers has twice been advanced by the Commerce Committee, said Senator John Thune of South Dakota, the Republican chairman.