Ocean heating doubles

The ocean is taking heat. That’s the conclusion of a new study that finds that Earth’s oceans now absorb heat at twice the rate they did 18 years ago. Around half of ocean heat uptake since 1865 has taken place since 1997, researchers also report online January 18 in Nature Climate Change.

Warming waters are known to contribute to coral bleaching (SN Online: 10/8/15) and they take up more space than cooler waters, raising sea levels. While the top of the ocean is well studied, its depths are trickier to query. The researchers gathered 150 years of ocean temperature data in order to get a better picture of heat uptake from surface to seabed. They compiled temperature readings collected by everything from a 19th century sailing expedition of the HMS Challenger to modern automated ocean probes. The far-flung data sources, combined with computer simulations, created a timeline of ocean temperature changes, including cooling from volcanic eruptions and warming from fossil fuel emissions.

About 35 percent of the heat taken in by the oceans during the industrial era now resides at a depth of more than 700 meters, the researchers found. They say they’re unsure whether the deep-sea warming offset warming at the sea’s surface.