A new University of Washington study reveals why the Antarctic Ocean might be one of the last places to experience the effects of global warming and human-driven climate change.
Over the years, the water surrounding Antarctica has stayed roughly the same temperature even as the rest of the planet continues to warm, a fact often pointed out by climate change deniers.
Now, a new study uses observations and climate models to suggest that the reason for this inconsistency is due to the unique currents around Antarctica that continually pull deep, old water up to the surface. This ancient water hasn't touched the Earth's surface since before the machine age, meaning it has been hidden from human-driven climate change.
"With rising carbon dioxide you would expect more warming at both poles, but we only see it at one of the poles, so something else must be going on," said Kyle Armour of the University of Washington and lead author of the study. "We show that it's for really simple reasons, and ocean currents are the hero here."
Although climate models typically cite churning seas mixing extra heat downward as the cause of the inconsistent warming observed in the Antarctic ocean, the new study traces the path of the missing heat and reveals that this explanation doesn't fit.
"The old idea was that heat taken up at the surface would just mix downward, and that's the reason for the slow warming," Armour said. "But the observations show that heat is actually being carried away from Antarctica, northward along the surface."
Using dyes in model simulations, the team showed that the seawater that has experienced the most climate change typically congregates around the North Pole, while Antarctica remains relatively unchanged. These findings explain why the Arctic's ocean and sea ice seem to have been affected the most by global warming.
"The oceans are acting to enhance warming in the Arctic while damping warming around Antarctica," Armour said. "You can't directly compare warming at the poles, because it's occurring on top of very different ocean circulations."
Understanding where extra heat goes and determining the forces that are pushing the uneven temperatures at the poles is essential for better understanding climate change and global warming.
"When we hear the term 'global warming,' we think of warming everywhere at the same rate," Armour said. "We are moving away from this idea of global warming and more toward the idea of regional patterns of warming, which are strongly shaped by ocean currents."
The findings were published in the May 30 issue of Nature Geoscience.