Mind Your Head! Scientists Predict Mid-Century Atlantic Ocean Current Collapse

"Shutting down the AMOC can have very serious consequences for Earth's climate, for example, by changing how heat and precipitation are distributed globally. While a cooling of Europe may seem less severe as the globe as a whole becomes warmer and heat waves occur more frequently, this shutdown will contribute to increased warming of the tropics, where rising temperatures have already given rise to challenging living conditions," says Professor Peter Ditlevsen from the Niels Bohr Institute. "Our result underscores the importance of reducing global greenhouse gas emissions as soon as possible," says the researcher. The calculations, just published in the scientific journal, Nature Communications, contradict the message of the latest IPCC report, which, based on climate model simulations, considers an abrupt change in the thermohaline circulation very unlikely during this century.

On studies of early warning signs that ocean currents exhibit when they become unstable, the researchers' forecast is predicated. These Thermohaline Circulation Early Warning Signals have been observed in the past, but it has only recently become able to estimate when a collapse will take place thanks to the development of sophisticated statistical techniques. 

The researchers analyzed sea surface temperatures in a specific area of the North Atlantic from 1870 to the present day. These sea surface temperatures are "fingerprints" testifying to the strength of the AMOC, which has only been measured directly for the past 15 years. "Using new and improved statistical tools, we've made calculations that provide a more robust estimate of when a collapse of the Thermohaline Circulation is most likely to occur, something we had not been able to do before," explains Professor Susanne Ditlevsen of UCPH's Department of Mathematical Sciences. The thermohaline circulation has operated in its present mode since the last ice age when the circulation indeed collapsed.

Abrupt climate jumps between the present state of the AMOC and the collapsed state have been observed to happen 25 times in connection with ice-age climate. These are the famed Dansgaard-Oeschger events first observed in ice cores from the Greenlandic ice sheet. At those events, climate changes were extreme with 10-15 degrees changes over a decade, while present-day climate change is 1.5 degrees warming over a century. Facts: The Atlantic Meridional Overturning Circulation (AMOC) is part of a global system of ocean currents. By far, it accounts for the most significant part of heat redistribution from the tropics to the northernmost regions of the Atlantic region -- not least to Western Europe.

At the northernmost latitudes, circulation ensures that surface water is converted into deep, southbound ocean currents. The transformation creates space for additional surface water to be moved northward from equatorial regions. As such, thermohaline circulation is critical for maintaining the relatively mild climate of the North Atlantic region.
The work is supported by TiPES, a joint-European research collaboration focused on tipping points of the climate system. The TiPES project is an EU Horizon 2020 interdisciplinary climate research project focused on tipping points in the climate system.

Source:

University of Copenhagen - Faculty of Science. "Gloomy climate calculation: Scientists predict a collapse of the Atlantic ocean current to happen mid-century." ScienceDaily. ScienceDaily, 25 July 2023. <www.sciencedaily.com/releases/2023/07/230725123122.htm>

Marjorie Farrington July 2023