A major Atlantic Ocean current helps regulate how much heat the planet stores, and its projected weakening as the climate warms could accelerate global warming, according to new research led by an Oregon State University scientist.
The Atlantic Meridional Overturning Circulation, or AMOC, carries warm water northward through the Atlantic and colder water southward. It has remained relatively stable for nearly 12,000 years, since the end of the last Ice Age.
But climate models project that human-caused climate change could weaken the current. New research published in Nature Geoscience suggests that could cause the planet to retain more heat.
"We can use those natural changes of our climate as a way to better understand our planet," said Christo Buizert, an Oregon State University paleoclimatologist and lead author of the study. "You can think of it as Mother Nature's own little experiments."
Researchers examined abrupt changes in the AMOC during past ice ages to better understand how the current affects the planet's temperature.
Scientists have traditionally described the AMOC's role as a kind of “bipolar seesaw”: When the North Atlantic cooled during periods of weaker circulation, the Southern Hemisphere warmed.
But Buizert and his colleagues found the current does more than redistribute heat between the Northern and Southern hemispheres. A strong AMOC also helps the planet shed heat. When the current weakens, more heat remains stored in the ocean.
“When this AMOC is running strong, it's actually extracting heat from the entire ocean,” Buizert said. “When it slows down, that heat builds up globally rather than moving north.”
That means a weaker AMOC could amplify the warming already caused by greenhouse gas emissions.
“The ocean and the atmosphere are kind of working together to make sure that when this AMOC is weak, the entire planet is gaining more energy, more heat,” Buizert said.
Changes in the AMOC during the last Ice Age produced additional warming equivalent to about 10 years of current human greenhouse gas emissions, according to the study.
That doesn't mean the same thing will necessarily happen as the climate warms today. Buizert said past changes are not a perfect comparison for the modern climate.
The research also suggests the AMOC could be more stable in a warmer world than it was during the last Ice Age. Climate change is still expected to weaken the circulation, but the findings suggest an irreversible collapse may be less likely.
“It might weaken a little bit, but we predict it will recover,” Buizert said.
Guest
- Christo Buizert, professor of geology and geophysics, Oregon State University
