Ocean Warming in the Southern Hemisphere May be Far Higher Than Previously Thought

It turns out that ocean warming in the Southern Hemisphere may have been underestimated. After using satellite observations and a suite of climate models, scientists have discovered that ocean temperatures may be rising far higher than expected.

"This underestimation is the result of poor sampling prior to the last decade and limitations of the analysis methods that conservatively estimated temperature changes in data-sparse regions," said Paul Durack, lead author of the new paper, in a news release.

In this latest study, the scientists found that climate models that simulate the relative increase in sea surface height, which is a leading indicator of climate change, between Northern and Southern hemispheres is consistent with highly accurate altimeter observations. That said, when they separated the simulated upper-ocean warming in the Northern and Southern Hemispheres, they found it was inconsistent with observed estimates of ocean heat content change. Because these sea level and ocean heat content changes should be consistent, this suggests that Southern Hemisphere ocean heat content changes were likely underestimated.

"Prior to 2004, research has been very limited by the poor measurement coverage," said Durack. "By using this satellite data, along with a large suite of climate model simulations, our results suggest that global ocean warming has been underestimated by 24 to 58 percent. 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."

Most of the excess heat associated with global warming is absorbed by the oceans. This means that the amount of heat the oceans contain is an important part of assessing Earth's overall energy budget. In fact, ocean heat storage accounts for more than 90 percent of Earth's excess heat that is associated with warming temperatures.

The findings could help with future research. By learning that the southern oceans had more heat than predicted, scientists can now move forward with and correct climate models.

The findings are published in two articles in Nature Climate Change here and here.