02-21 Melting glacier ice in Greenland

[Image above] The melting Greenland ice sheet is introducing an influx of cold, fresh water into the Atlantic Ocean that destabilizes the ocean’s current system, which plays an essential role in regulating global climate. Credit: GRID-Arendal, Flickr (CC BY-NC-SA 2.0)

Even before Russia’s invasion of Ukraine in February 2022, energy prices were making headlines across Europe. As reported on CTT in November 2021, a confluence of factors, including colder-than-average winters and drought conditions, was driving unusually strong demand for natural gas for power generation. Yet Gazprom, a Russian majority state-owned company and the single largest supplier of natural gas to the European market, was unable to deliver additional volume to fulfill this demand.

Since the Russia–Ukraine war started, discussions on the energy ecosystem in Europe intensified. In October 2022, the Council of the European Union agreed to an emergency regulation to address high gas prices through new measures on joint gas purchasing, price limiting mechanisms, and transparent infrastructure use. Those measures, which were in effect through March 2023, reduced gas consumption by around 15% and decreased reliance on Russian supplies of pipeline gas from 40% down to 9%.

Even as gas and electricity markets stabilized, the European Commission and European Union members continued work to reduce Europe’s dependence on fossil fuels and accelerate the transition to green energy. The REPowerEU Plan, which supports projects in renewable energy, net-zero technologies, and workforce development, launched in May 2022 and received additional financing in July 2023.

Yet Europe’s efforts to establish a self-sustainable energy sector may face complications from another threat that might occur sooner than previously theorized—collapse of the Atlantic meridional overturning circulation (AMOC).

The AMOC is a system of surface-level and deep currents in the Atlantic Ocean. This system helps regulate global and regional climate by carrying warm, salty surface waters up north and colder, deep waters back down south.

Changes in temperature and salinity affect the flow of AMOC currents, and multiple studies have found that the AMOC’s flow has slowed considerably in recent decades. While this weakening is driven partly by natural variations in the Earth’s climate system, human-caused climate change is also a significant factor. Specifically, the melting Greenland ice sheet is introducing an influx of cold, fresh water into the sea that destabilizes the well-defined temperature-density gradients essential to the AMOC’s flow.

Over large timescales, the AMOC naturally switches between a strong, fast circulation and a much weaker, slower circulation. However, scientists are concerned that because of the additional temperature and salinity changes resulting from human-caused climate change, the AMOC may cease functioning altogether rather than just slowing down. The video below provides an accessible explanation of this process.

Credit: ThePrint, YouTube

The 2004 film The Day After Tomorrow depicted a highly fictionalized account of what may occur if the AMOC collapses. However, a 2019 report by the United Nations’ Intergovernmental Panel on Climate Change (IPCC) concluded a full collapse of the AMOC would be unlikely this century, and it generally downplayed disaster scenarios.

But debate around the AMOC’s potential collapse was reinvigorated last summer when Peter and Susanne Ditlevsen, professors in physics and statistics, respectively, at the University of Copenhagen, published an open-access paper in July 2023 suggesting a high likelihood of AMOC collapse between 2025–2095, with a central estimate of 2057.

The Ditlevsens reached this conclusion using a new model that most experts agree is mathematically rigorous and internally consistent. However, many in the scientific community questioned the model’s 95% confidence interval.

The model relies on observations of sea surface temperatures from one region in the North Atlantic to extrapolate the future of the entire ocean system. The assumption that these observations can represent the whole system “needs to be further tested,” says Levke Caesar, an AMOC expert at the University of Bremen in Germany, in a Scientific American article.

Despite these critiques, other studies published in 2021 and 2022 confirm that the AMOC may be approaching a tipping point sooner than the IPCC’s prediction. And if collapse does occur, it would have widespread global consequences, as described in the Scientific American article.

For example, parts of Europe could experience significant cooling by as much as 5 or 10 degrees Celsius. Meanwhile, tropical rain belts might shift their positions, causing drought in some regions but flooding in others.

Additionally, if the AMOC can no longer ferry large volumes of water around the world, the ocean may absorb less carbon dioxide from the atmosphere. Plus, parts of the deep ocean may receive less oxygen.

Knowing these potential ramifications, “I think this risk should be taken very seriously,” writes Stefan Rahmstorf, an ocean expert at the Potsdam Institute for Climate Impact Research, in a RealClimate blog post.