VOA科学技术2024--Study: Collapse of Ocean Currents Could Cause Major Climate Problems（在线收听）

Study: Collapse of Ocean Currents Could Cause Major Climate Problems

　　Scientists are warning of the possible collapse of an Atlantic Ocean current system that would likely lead to worldwide climate changes.

　　Researchers identify the ocean system as the Atlantic Meridional Overturning Circulation (AMOC). They say the system plays an important part in moving, or circulating, salt and warm water around the world. This process helps control world temperatures, affects carbon dioxide levels and supports worldwide water flows.

　　The AMOC system brings warm water to northern areas and carries cold water south, the U.S. National Oceanic and Atmospheric Administration (NOAA) explains. The circulation also transports nutrients necessary to support many kinds of sea life.

　　The process begins as warm and salty surface water flows northward toward Greenland in the Atlantic.

　　Scientists created "a complex climate model" in an effort to simulate a possible collapse of the AMOC. The computer model was "able to measure a sudden weakening of the ocean circulation," the team said in a statement.

　　The research was led by scientists from Utrecht University in the Netherlands. A study describing their findings recently appeared in the publication Science Advances.

　　For thousands of years, Earth's oceans have depended on the AMOC circulation system – which acts like a conveyor belt - to control climate. The system is still operating, but has experienced slowdowns in recent years.

　　The driver of the conveyor belt sits off the coast of Greenland. As more ice melts here from climate change, more freshwater flows into the North Atlantic and slows the circulation, said Rene van Westen. He is a climate scientist and oceanographer at Utrecht University.

　　Van Westen told The Associated Press his research on a possible AMOC collapse does suggest "we are heading towards a tipping point." He added, however, that while his team found clear evidence the system is moving closer to collapse, "we're not sure how much closer."

　　In the current system, cold, deeper and fresher water heads south past both Americas and then east past Africa. The system also pushes saltier, warmer ocean water from the Pacific and Indian oceans past the southern tip of Africa. This water flows to and around Florida before continuing up the U.S. East Coast towards Greenland.

　　The Dutch team simulated 2,200 years of AMOC flow. The researchers added to the model expectations for future human-caused climate change. The results predicted "an abrupt AMOC collapse," after 1,750 years.

　　But the researchers noted it is difficult to provide a realistic date because the process could be influenced by many unknown circulation events. Making a prediction is also difficult because "current observational records are too short" to provide an exact estimation of collapse, the scientists said. The team said more physics-based measuring tools are necessary to create early warning systems.

　　The team noted one difficult area to predict is around the tip of Africa, where it is difficult to produce realistic estimates of circulation flows. Measurements around that area have a big effect on how much the AMOC slows, the researchers said.

　　"This value is getting more negative under climate change," van Westen said. He added that when the AMOC reaches a certain level, the change does not happen over time, but would be more "cliff-like," he added.

　　Van Westen said an AMOC collapse would mostly affect climate in Europe.

　　The researchers say a collapse could reduce temperatures in northwestern Europe by 5 to 15 degrees Celsius. Their study predicts the change would also extend Arctic ice much farther south, raise temperatures in the Southern Hemisphere and change worldwide rainfall. Some scientists warned the climate effects could cause worldwide food and water shortages.

　　In addition, the team said the simulation predicted a possible 100 centimeter rise in European sea levels if the AMOC collapsed.

　　Van Westen warned that once the collapse happens, the resulting climate effects are nearly impossible to change. Another member of the team, Henk Dijkstra, said staying clear of such a tipping point is necessary to avoid the "devastating consequences on climate, society, and the environment."

　　Words in This Story

　　simulate – v. to do or make something that behaves or looks like something real but is not

　　conveyor belt – n. a continuously moving piece of equipment used to transport objects from one place to another

　　tipping point – n. the time at which a change or effect cannot be stopped

　　abrupt – adj. sudden and unexpected

　　negative – adj. harmful or bad

　　cliff – n. a high area of rock with a very steep side, often along a coast

　　devastating – adj. causing a lot of damage or destruction

　　consequence – n. a result of a particular action or situation, often one that is bad