The Southern Ocean around Antarctica has been expected to warm as a result of global climate change for decades, according to climate models. But scientists have discovered a startling trend: this enormous body of water has actually cooled over the last 40 years.
Researchers from Stanford University have uncovered the primary reason behind this unexpected cooling. Their study, published in Geophysical Research Letters, points to underestimated rainfall and missing meltwater from Antarctic ice sheets as the key factors. As global temperatures rise, Antarctica’s ice sheets melt at an accelerated rate, releasing massive amounts of freshwater into the ocean. This, combined with increased precipitation, makes the surface waters less salty and less dense.
According to the study’s senior author and assistant professor of Earth system science, Earle Wilson, this freshened upper layer acts as a barrier to stop warm waters from below from mixing. “The fresher you make that surface layer, the harder it is to mix warm water up,” he says. The majority of climate models have greatly exaggerated the warming of the Southern Ocean because they do not take these freshwater dynamics into consideration.
Given how important the Southern Ocean is in controlling Earth’s climate, this revelation is significant. Large volumes of carbon dioxide and surplus heat are absorbed by it, affecting sea level rise, global weather patterns, and phenomena like El Niño and La Niña. Researchers caution that further departure from model projections could modify our expectations for the effects of climate change, even though recent warming outbursts have somewhat counterbalanced the cooling trend.
In order to help scientists and politicians better prepare for the difficulties that lie ahead, Wilson highlights the need for enhanced climate models that take these freshwater factors into account.
