Washington ? The wind, a favorite power source of the green energy movement, seems to be dying down across the United States. And the cause, ironically, may be global warming — the very problem wind power seeks to address.

The idea that winds may be slowing is still a speculative one, and scientists disagree whether that is happening. But a first-of-its-kind study suggests that average and peak wind speeds have been noticeably slowing since 1973, especially in the Midwest and the East.

“It’s a very large effect,” said study co-author Eugene Takle, a professor of atmospheric science at Iowa State University. In some places in the Midwest, the trend shows a 10 percent drop or more over a decade. That adds up when the average wind speed in the region is about 10 to 12 miles per hour.

There’s been a jump in the number of low or no wind days in the Midwest, said the study’s lead author, Sara Pryor, an atmospheric scientist at Indiana University.