Warming is not equal across the planet.
There are likely only a couple places left in the world that are untouched by the effects of human-driven climate change, and the ocean water surrounding Antarctica is one of them. The water has remained around the same temperature even though most of the planet has warmed.
Climate change deniers often use this scientific conundrum to further the argument that climate change is not real. However, new research from the University of Washington and the Massachusetts Institute of Technology just tossed away one of the last straws grasped by deniers. It turns out this inconsistent pattern of warming is caused by ocean currents.
According to the results of the paper published in the journal Nature Geoscience, Antarctica is surrounded by unique currents. These currents are continuously pulling deep, centuries-old water (water that has not been in contact with Earth’s atmosphere since before the industrial revolution) up to the surface — meaning this water has never experienced any fossil-fuel related 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 lead author Kyle Armour, a UW assistant professor of oceanography and of atmospheric sciences, in a press release. "We show that it's for really simple reasons, and ocean currents are the hero here."
Photo credit: K. Armour/UW. Observed warming over the past 50 years (in degrees Celsius per decade) shows rapid warming in the Arctic, while the Southern Ocean around Antarctica remains relatively unchanged.
Strong westerly winds around Antarctica push surface waters north, drawing up water from below. But since the Southern Ocean’s water comes from extremely deep regions, it takes centuries before the water rising to the surface experiences our modern global warming. On the other hand, ocean waters on the west coast of America, for example, only draw water up from a depth of a few hundred meters.
"The Southern Ocean is unique because it's bringing water up from several thousand meters [as much as 2 miles]," Armour said. "It's really deep, old water that's coming up to the surface, all around the continent."
This delayed Antarctic Ocean warming has been recognized in global climate models, and it was thought that the region’s ice-cold water was mixing the extra heat downward. But using observational data to trace the path of the heat, it turns out it "is actually being carried away from Antarctica, northward along the surface," said Armour.
What’s more, this northward movement of the ocean’s surface water continues all the way up to the Arctic. In fact, by using dyes in model simulations, the researchers were able to show that this warmer water gathers together in the Arctic. Yet another reason why the Arctic is dealing with significant melt, while the continent of Antarctica is growing slightly in size.
"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."
This information will definitely help scientists more accurately predict future global temperatures, but as the results of the study clearly indicate, warming is not equal across the planet.
"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."