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Why L.A.'s Fog Is Disappearing

A new study says warming caused by urbanization is to blame.
The frequency of fog in Los Angeles has decreased since this photo was taken in 1994.
The frequency of fog in Los Angeles has decreased since this photo was taken in 1994. AP images

Foggy weather doesn't have many fans, especially in sunny places like Los Angeles. But Angelino fog haters can rejoice, because there isn't nearly as much nighttime and early morning fog in the city now as there used to be. The frequency of fog over L.A. has reduced by 63 percent since 1948, according to a new study by researchers at Columbia University, which will be published in Geophysical Research Letters this month.

The researchers analyzed hourly cloud height measurements taken by airports around the Southern California region during the past 70 years. They found that mostly urbanized areas had both higher nightly temperatures and cloud heights—a clear sign of the heat island effect, which causes urban areas to be hotter than their surrounding rural areas, says Park Williams, one of the study authors.