“When carbon emission rates are at present day levels and higher, we see greater basin average sea level rise in the Atlantic relative to the Pacific,” says Krasting. “This also means that single global average measures of sea level rise become less representative of the regional scale changes that we show in the study.”
In the new research, the scientists used a high powered climate change model based at the Geophysical Fluid Dynamics Laboratory in Princeton, N.J., that simulates the ocean, the atmosphere and the cycling of carbon throughout the Earth system. The goal was to determine how much sea level rise would occur in the Atlantic, versus the Pacific, under a variety of global carbon emissions scenarios.
And the simulation found that at high emissions scenarios similar to current rates, the Atlantic sea levels rise considerably faster than the Pacific, with particularly noteworthy impacts for the U.S. East Coast. (Other recent research by scientists with the U.S. Geological Survey has suggested this increased rate of sea level rise is already happening — finding sea level rise rates “~ 3–4 times higher than the global average” along a large stretch of the U.S. East Coast, which the researchers dubbed a sea level rise “hotspot.”)
The reason for the difference, the researchers say, is that the Atlantic, more than the Pacific, is characterized by a strong “overturning” ocean circulation — technically known as the Atlantic Meridional Overturning Circulation, or AMOC — that spans the north-south length of the globe and ultimately connects waters off New York with those at the tip of Antarctica. This means that waters circulate through the entire Atlantic much faster than they do throughout the Pacific: A “parcel” of water that sinks beneath the surface in the Atlantic will generally make it back to the surface again in 200 to 300 years, versus about three times as long for the Pacific, Krasting explains.
For this reason, scientists sometimes say that Atlantic waters are “younger” than Pacific waters.
Another way of putting it is that the Atlantic waters “ventilate” more, plunging from the surface to great depths before eventually making their way back to the surface again. But if this circulation slows due to climate change, the study finds, less cold water will dive to ocean depths in the North and far South Atlantic (technically called “deep water formation”), leading to warmer water pooling below the surface and, ultimately, greater warming overall.
“The average temperature of the basin actually goes up, because you’re not bringing that cool water,” says Krasting. Warm water expands, and that’s the cause of the sea level rise expected in the study.