June 27, 2017

New study shows our oceans are heating rapidly

Climate change is causing ocean temperatures to rise at a rapid rate, no matter which group of statistics are used to gauge the increase, according to a new analysis published this week in the journal Climate Dynamics that used three unique sets of data to confirm the discovery.

In their new paper, Dr. Gonjgie Wang from the Institute of Meteorology and Oceanography at China’s PLA University of Science and Technology, University of St. Thomas thermal and fluid sciences professor John Abraham and their colleagues reviewed three distinct ocean temperature measurements collected by different groups and found that each confirmed ocean warming.

“Although there’s some uncertainty in the distribution among Earth’s ocean basins, there’s no question that the ocean is heating rapidly,” Thomas wrote in an article published Monday by The Guardian. He added that the findings represented “a significant advancement” in such research, which reached the conclusion that “regardless of how you measure, who does the measurements, when or where the measurements are taken, we are warming.”

Calling ocean temperatures “the most important measurement of global warming,” the professor explained that scientists need to use data collected by several sensors spread out across the globe and placed at various depths. Furthermore, he said, these measurements need to be collected over several decades so that the researchers can establish long-term climate-related trends.

Study authors explain why climate data is not always in agreement

In the new study, Thomas said that he and his colleagues examined the three main factors which can impact the accuracy of ocean temperature data: “hot” or “cold” biases inherent in the sensors used to gather data, the lack of sensors in all locations at any given time, and the selection of the climate “baseline” used by experts for the sake of comparison to current heating trends.

Sensor biases, he explained, can depend on how the water is tested. For instance, water collected in buckets for measurements tended to be slightly cooler than water that was tested using sensors placed directly on a ship’s hull (which were closer to the vessel’s engines). Similar biases can be seen throughout the years when oceanographers obtain new technology, Thomas said. In order to obtain an accurate measurement of water temperature change, such biases must be removed.

In terms of coverage, much of the current climate data comes from the ARGO fleet – a group of around 3,800 devices spread out throughout the ocean. However, Thomas noted, this information only dates back to the fleet’s launch in 2005. Before then, ocean temperature measurements were not uniform, and scientists were forced to fill in the gaps using a “mapping” strategy. Finally, the choice of baseline climatology is essential to determining how much temperatures have increased and over how long of a period of time, he wrote.

In their study, Thomas said that he and his colleagues “looked at the different ways that three groups make decisions about mapping, bias, and climatology. We not only asked how much the oceans are warming, but how the warming differs for various areas (ocean basins) and various depths. We found that each ocean basin has warmed significantly.” While there were differences amongst the three groups, he said, each dataset agrees that ocean temperatures are on the rise.

“Our study confirms again a robust global ocean warming since 1970,” Dr. Wang explained. “However, there is substantial uncertainty in decadal scale ocean heat redistribution, which explains the contradictory results related to the ocean heat changes during the ‘slowdown’ of global warming in the recent decade. Therefore, we recommend a comprehensive evaluation in the future for the existing ocean subsurface temperature datasets.”


Image credit: Unsplash/Martin Dorch