Ocean Warming in Southern Hemisphere Worse Than We Thought

Oceans in the Southern Hemisphere, which make up 60 percent of the world's oceans, are warming far worse than previously thought, according to a new study.

Using satellite observations and a large collection of climate models, Lawrence Livermore National Laboratory (LLNL) scientists have found that long-term ocean warming in the upper 700 meters (~2,300 feet) of Southern Hemisphere oceans has likely been underestimated.

"This underestimation is a result of poor sampling prior to the last decade and limitations of the analysis methods that conservatively estimated temperature changes in data-sparse regions," LLNL oceanographer Paul Durack, the study's lead author, said in a statement.

Ocean's are one of the Earth's major carbon sinks, accounting for more than 90 percent of the planet's excess heat that is associated with global warming. The more greenhouse gases, like carbon dioxide, that are emitted into the atmosphere, the more the oceans work to trap these emissions.

According to the study, measurements of sea surface height - a major indicator of climate change - based on climate models of the Southern Hemisphere is inconsistent with observed estimates of ocean heat content change. Obviously sea level and ocean heat content changes should be consistent, and suggest that until recent improvements occurred in the observational system in the early 21st century, Southern Hemisphere ocean heat content changes were likely underestimated.

Since 2004, automated profiling floats - named Argo - have been used to measure global ocean temperatures from the surface down to 2,000 meters (6,561 feet). These Argo floats for the first time provide global ocean provide systematic estimates of the Southern Hemisphere, and have shown that the region's oceans are gradually warming - more so than previously thought.

"Our results suggest that global ocean warming has been underestimated by 24 to 58 percent," Durack explained. "The conclusion that warming has been underestimated agrees with previous studies, however it's the first time that scientists have tried to estimate how much heat we've missed."

The results were published in the journal Nature Climate Change.