Man-made heat put in oceans has doubled since 1997

Changes in ocean heat storage are important because the ocean absorbs more than 90 percent of the Earth’s excess heat increase that is associated with global warming. Scientists said it is vital to continue studying this and other ocean depths in the coming decades.

Scientists found that the vast majority of additional absorbed heat in the ocean exists toward the bottom, 35 percent of which can be found deeper than 700 meters below the surface.

One outside scientist, Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, also has been looking at ocean heat content and he said his ongoing work shows the Gleckler team “significantly underestimates” how much heat the ocean has absorbed.

Each robot hovers at about 3,300 feet deep and periodically dives more than a mile down before surfacing to transmit temperatures, salinity and changing ocean currents to shore stations around the world.

And more than a third of the surge in heat in the oceans since 1997 was at depths exceeding 700 meters – a part of the ocean rarely studied, the scientists wrote in the journal Nature Climate Change.

The world’s oceans are warming at a quickening rate, with the past 20 years accounting for half of the increase in ocean heat content that has occurred since pre-industrial times, a new study has found.

“Given the importance of the ocean warming signal for understanding our changing climate, it is high time to measure the global ocean systematically from the surface to the ocean floor”, said NOAA oceanographer Gregory Johnson.

Researchers found that world’s oceans absorbed a total of 150 zettajoules over the course of 132 years at the start of industrial era (from 1865 to 1997) and absorbed another 150 zettajoules in next 18 years from 1998 to 2015. “The actual temperature change is relatively small, but due to the huge heat capacity of the oceans this equates to a very, very large heat content change”.

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. Not exactly. Even a small uptick in the icy temperatures of the deep ocean will cause water to thermally expand.

“We’re now seeing that more and more of the heat from global warming is going into the deeper layers of the oceans, ” Gleckler said in a telephone interview. Gawarkiewicz adds that warming will affect fragile deep ocean ecosystems, including cold water corals, as well as large-scale atmospheric and ocean circulation patterns.

At current rates, Earth is on track for warming of about three degrees Celsius by the end of the century. Some experts had suggested it was a sign of a pause in warming overall, but this new study reveals that all that heat thought to have been “paused” was actually taken up by the depths of the ocean.

To address this, the study compares the different observational datasets with simulations from climate models (CMIP5) used in the latest Intergovernmental Panel on Climate Change, forced with historically realistic levels of greenhouse gases, emissions from land use, changes in solar activity and the temporary cooling effect of volcanic eruptions.