Scientists have found 500 seabed vents bubbling methane into the Pacific Ocean off the United States, roughly doubling the number of known U.S. seeps of the powerful greenhouse gas, a study showed Wednesday.

Methane naturally escapes from the sea floor in many places around the world and can stoke global warming if it reaches the atmosphere. Worldwide, scientists are trying to see if rising ocean temperatures cause more leaks.

"It appears that the entire coast off Washington, Oregon and California is a giant methane seep," Robert Ballard, who is famed for finding the wreck of the Titanic and has now discovered the 500 new seeps, said in a statement.