WASHINGTON (AP) – A study shows the amount of man-made heat energy the oceans have absorbed since 1997 is equivalent to a Hiroshima-style bomb being exploded every second for 75 straight years. That’s double the heat energy the waters were absorbing before 1997.

Scientists have long known that more than 90 percent of the heat energy from man-made global warming goes into the world’s oceans instead of the ground. And they’ve seen ocean heat content rise in recent years. But the study published Monday in the journal Nature Climate Change tracks how much man-made heat has been buried in the oceans in the past 150 years.

The study’s authors used ocean-observing data that goes back to the British research ship Challenger in the 1870s and high-tech modern underwater monitors and computer models.