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Cooling: Slowing ocean circulation could limit Arctic temperature rise

A map depicting the direction in which the AMOC transports warm water from the tropics to high latitudes. Credit: R. Currie, Woods Hole Oceanographic Institution/Science/USGCRP

The Arctic is warming three to four times faster than the global average. But new research suggests that slowing major ocean currents could reduce projected Arctic warming by up to 2C by the end of this century.

Scientists have been warning for years that unchecked warming in the Arctic could have devastating consequences, threatening wildlife and ushering in an era of more frequent extreme weather events. Amid concerns about these types of outcomes, a study led by the University of California, Riverside offers limited relief.

The study, published in the Proceedings of the National Academy of Sciences, investigated how the slowing of the Atlantic Meridional Overturning Circulation (AMOC) affects the Arctic climate. The AMOC is an ocean current that transports heat from the tropics to higher latitudes.

Arctic temperatures are predicted to rise by 10 degrees Celsius by the end of this century, but studies show that if the slowing of the AMOC flow is taken into account, Arctic temperatures will only rise by 8 degrees Celsius.

“AMOCs are important components of our climate system because they move heat around the planet,” said Yu-Chi Lee, a graduate student in Earth and planetary sciences at UCR and lead author of the study. “We found that its weakening reduces the amount of heat reaching the North Pole, slowing the rate of warming.”

Despite this potential benefit, the study highlights continuing concerns for Arctic ecosystems. As sea ice melts, polar bears face habitat loss, which could make hunting and survival more difficult. Additionally, as the ice disappears, a darker outer water surface is exposed, absorbing more sunlight and further accelerating warming through a process called the albedo effect.

Although this slowdown may slightly reduce Arctic warming, researchers warn that it could lead to other climate changes. One of the biggest concerns is potential changes to the Tropical Convergence Zone, the tropical rain belt. As this rain belt moves southward, regions that rely on rainfall could experience more frequent droughts, affecting agriculture and water supplies.

There are also misconceptions about the relationship between sea ice and sea level rise. Just as melting ice in a glass does not cause the water to overflow, melting sea ice does not directly cause sea level rise because the ice is already in the water. However, land ice such as glaciers and the expansion of water due to rising water temperatures contribute to sea level rise. Although the slowing of the AMOC is not the primary driver of sea level rise, it does lead to other important changes in the climate system.

Wei Liu, associate professor of climate change at the University of California, Riverside and co-author of the paper, emphasized the complexity of AMOC’s role in the global climate. “While the AMOC slowdown may bring temporary relief to the Arctic, this is simply not good news,” Liu said. “The overall impact on ecosystems and weather patterns, both in the Arctic and globally, could still be severe.”

The research team used a coupled climate model that integrates interactions between the ocean, atmosphere, land, and sea ice. The researchers isolated the effects of AMOC by running two simulations. One is a simulation in which the AMOC slows down due to the effects of rising greenhouse gases, and the other is a simulation in which it artificially maintains its strength by removing fresh water from the North Atlantic and increasing its salinity.

“Our simulations allow us to clearly see how much future Arctic warming is related to slowing of the AMOC,” Lee said. “Even though the slowdown reduces warming by a few degrees, the overall impact on Arctic ecosystems and the Earth’s climate system remains severe.”

Li also emphasized that the economic slowdown started relatively recently and that scientists are still debating how long it has been going on and whether it will continue.

“Direct field observations of AMOC strength began around 2004, a relatively short period of time to draw long-term conclusions,” he said. “But there is research that suggests it could collapse by the end of this century, and that will have a major impact.”

Looking to the future, Lee continues to focus on the big picture. “While a slowdown in the AMOC may have short-term benefits, its far-reaching effects show that even small changes in ocean circulation can cause ripple effects across the planet. Climate change will never be “It’s not a regional issue,” she said. “The future of the Arctic, and the world, depends on how we respond today.”

Further information: Yu-Chi Lee et al., Impact of Atlantic Meridional Overturning Circulation Weakening on Arctic Amplification, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2402322121

Provided by University of California, Riverside

Citation: Cooling shift: Slowing ocean circulation could moderate Arctic temperature rise (October 26, 2024) https://phys.org/news/2024-10-cooling-shift-ocean- Retrieved October 26, 2024 from circulation-temper.html

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