Researchers predict the system of ocean currents that distributes cold and heat between the North Atlantic and tropics will completely stop if we continue to emit the same levels of greenhouse gases we do today.
Using advanced statistical tools and ocean temperature data from the last 150 years, the researchers calculated that the ocean current, known as the Thermohaline Circulation or the Atlantic Meridional Overturning Circulation (AMOC), will collapse—with 95% certainty—between 2025 and 2095.
This will most likely occur in 34 years, in 2057, and could result in major challenges, particularly warming in the tropics and increased storminess in the North Atlantic region.
“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 an increased warming of the tropics, where rising temperatures have already given rise to challenging living conditions,” says Peter Ditlevsen, a professor from the Niels Bohr Institute at the University of Copenhagen.
“Our result underscores the importance of reducing global greenhouse gas emissions as soon as possible.”
The calculations, published in 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.
The researchers’ prediction is based on observations of early warning signals that ocean currents exhibit as they become unstable. These early warning signals for the Thermohaline Circulation have been reported previously, but only now has the development of advanced statistical methods made it possible to predict just when a collapse will occur.
The researchers analyzed sea surface temperatures in a specific area of the North Atlantic from 1870 to present days. These sea surface temperatures are “fingerprints” testifying 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,” says Susanne Ditlevsen, professor in the mathematical sciences department.
The Thermohaline Circulation has operated in its present mode since the last ice age, where the circulation was indeed collapsed. Abrupt climate jumps between the present state of the AMOC and the collapsed state has 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 days climate change is 1.5 degrees warming over a century.
Source: University of Copenhagen
