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Europe Faces Millennial Megadroughts if Atlantic Ocean Current Collapses
A potential collapse of a critical Atlantic Ocean current could usher in an era of extreme and prolonged droughts across southern Europe, lasting for over a thousand years, according to a new study. Researchers have, for the first time, modeled the impact of a failing Atlantic Meridional Overturning Circulation (AMOC) on European summer precipitation under various climate scenarios, revealing a potentially devastating future.
The AMOC functions as a massive conveyor belt in the Atlantic Ocean, transporting heat from the Southern Hemisphere to the Northern Hemisphere and playing a vital role in regulating global climate patterns. Scientists have long warned that human-induced climate change is weakening this system, potentially pushing it towards a critical tipping point – thresholds in Earth’s climate system beyond which changes become self-perpetuating.
“The AMOC actually is already weakening,” explained Niklas Boers,a researcher at the Potsdam Institute for Climate Impact Research and lead author of the study. “The question is not if it will weaken, but when it will collapse.” The study, published in the journal Nature Climate Change, builds on previous research indicating that the AMOC is currently in its weakest state in over 1,600 years.
The researchers used complex climate models to simulate the effects of a collapsed AMOC, focusing on summer precipitation patterns across Europe. They began by establishing a baseline using ancient climate data, noting that carbon levels have already surpassed those historical benchmarks. The remaining four explored precipitation patterns under two scenarios: one where carbon emissions peak mid-century and then decline (known as RCP4.5),and another with significantly higher emissions (RCP8.5). Both scenarios were tested with varying levels of freshwater influx into the Atlantic Ocean.
Freshwater flooding, often resulting from melting icecaps, alters the ocean’s salinity and density, disrupting its ability to transport energy. In the RCP4.5 models, a considerable influx of freshwater led to AMOC collapse, while a smaller amount allowed the current to recover. The RCP8.5 simulations, representing a future with carbon emissions three times higher than present levels, consistently resulted in AMOC collapse nonetheless of freshwater input.
Researchers identified the RCP4.5 scenarios as the most realistic. “Under climate change, you’re getting more evaporation and your dry season becomes drier,” a lead author on the study stated, noting this phenomenon is already well-documented. “If you add AMOC collapse on top of that, you’re going to get more drought extremes.”
The data reveals a stark contrast in projected drought intensification. Across Europe as a whole, dry season intensity – the difference between evaporation and precipitation – is expected to increase by 8% under an RCP4.5 scenario with a functioning AMOC. Though, with a collapsed AMOC, that intensity surges to 28%.
The impact will not be uniform across the continent. For example, Sweden could experience a 54% increase in dry season severity with the AMOC intact, rising to 72% without it. Spain, already grappling with severe drought conditions, faces a 40% increase with the AMOC and a 60% increase without. [Placeholder for a map illustrating regional drought intensity projections].
These simulations focus on stable climate states, differing from the current period of rapid global warming. “We’re interested in what the mean responses are with different kinds of AMOC states in the background,” the researcher explained. Another climate scientist at the University of Leipzig in Germany lauded the study’s focus on long-term equilibrium. “The beauty of these simulations is that they look at hundreds of years after everything has changed,” he said. “The transient scenario where we plan for the next 100 years is different to an equilibrium scenario.”
Though, a professor of climate science at the University of Reading, U.K., cautioned against interpreting the study’s theoretical results as definitive predictions.”To get the AMOC to ‘collapse’ in this particular model, the authors need to add huge amounts of additional freshwater into the North Atlantic [and] that is not realistic,” he noted. “But it might very well be taken as a warning about what might be possible under the rather extreme scenario of an AMOC ‘collapse’.”
Despite these caveats, the overarching message is clear, according to a co-head of the research department on Earth system analysis at the Potsdam Institute for Climate Impact Research in Germany. “The increasing drought problems expected in any case due to global warming would be made even worse by a major AMOC weakening, and the latter looks increasingly likely,” he stated. “If the AMOC shuts down, this would have consequences for at least a thousand
