New research suggests a potential "collapse" of key Atlantic ocean currents could cause dramatic drop in winter temperatures across northern Europe, which would also overcome human-caused warming activity. This study, published in Geophysical Research Letters, examines the combined impact of the cessation of the Atlantic Meridional Overturning Circulation (AMOC) and global warming on temperatures in northern Europe.

What is AMOC?

The AMOC is a system of ocean currents that plays a role in essential role in keeping Europe warm. It transports warm water northward from the tropics to Europe and cold, deep water back south. This system is considered by some scientists to be a “tipping point” that, if triggered, would be irreversible on a human timescale. The collapse of the AMOC is often referred to as a “halt” or “breakdown.” The potential collapse of these ocean currents could be caused by the influx of freshwater from melting ice, as well as rising air temperatures.

Scientific debate and risks

Although there is considerable scientific debate about whether human-induced climate change is causing the AMOC to slow down and when it might reach a “tipping point,” some scientists estimate that the collapse could occur as early as this century. Previous work by the study’s lead author, Dr. René van Westen, found that the current state of the AMOC is on a trajectory toward tipping. That work also suggested a drop in average monthly winter temperatures in northern Europe of 10-30°C and a “drastic shift” in precipitation patterns in the Amazon.

New research findings

In their latest study, Van Westen and his colleagues focused on impact of the AMOC tipping event in combination with the impacts of climate change, rather than examining the collapse of ocean currents in isolation. The goal was to answer the question of whether warming caused by greenhouse gas emissions could offset the cooling from the AMOC collapse.

Scientists simulated the collapse of the AMOC under three global warming scenarios:

• Medium emissions scenario (RCP4.5), which is consistent with current global climate policies.
• Very high emissions scenario (RCP8.5), where warming will reach 4°C above the pre-industrial average by 2100.
• "Pre-industrial" scenario, without any man-made global warming.

In all scenarios, the researchers ran multiple simulations 500 years into the future, stabilizing global warming at 2°C and above 4°C by 2100. It is important to note that the study does not focus on when the AMOC might pass the tipping point, but rather on scenarios in the distant future when it has already happened. The simulation of the AMOC collapse in the model required the application of high levels of “unrealistic” freshwater inflow into the North Atlantic to overcome the “bias” in climate models that have an overly stable AMOC.

Implications for Europe

The most striking finding is that AMOC collapse in a world that is 2°C warmer will result in a colder Europe than it is todayIn this scenario, corresponding to medium emissions, northwestern Europe will face a “deep cooling”, characterized by more intense winter extremes.

• London could experience extremely cold winters with temperatures approaching -20°C.
• IN Donkey in Norway, winter extremes could drop to around -48°C.
• Average winter temperatures in London could be 1.9°C and in Oslo -16.5°C.
• Other cities, such as Edinburgh (-29.7°C) or Paris (-18°C), would also face extreme cold.

These low temperatures would be caused by the loss of heat transfer from the tropics via ocean currents, as well as the expansion of sea ice into northern Europe during the winter months. Although the winters would be extreme, summer temperatures would be expected to be only slightly cooler as in the pre-industrial era, which would mean dramatic temperature swings throughout the year. Professor Tim Lenton of the University of Exeter notes that such a scenario would mean “living like an ice age” in winter, while there would still be hot extremes in summer. Dr van Westen stresses that our social structure and infrastructure are not built for such extreme cold conditions.

Conversely, in a scenario where the world is 4°C warmer (very high emissions), cooling associated with the cessation of ocean currents would not outweigh global warmingNorthern Europe would not experience the large-scale expansion of sea ice or the strong cooling projected for a 2°C warming scenario. Instead, temperatures would be expected to increase throughout the year, especially in the summer months, although warming in Northern Europe would be less than the global average.

Future research and uncertainties

Experts who were not involved in the study acknowledged its importance but stressed the need for further research. Prof. Stefan Rahmstorf of Potsdam University said the new study was “very welcome” and confirmed long-standing concerns about the massive impacts of the AMOC collapse on European climate. Dr. Alejandra Sanchez-Franks of the National Oceanography Center, however, cautioned that the study used an idealized experiment and its conclusions related to the European climate 200 years after the AMOC change, not the immediate impacts. Dr. Yechul Chin of Seoul National University added that “significant uncertainties” remained that needed to be resolved for risk quantification and robust mitigation strategies.

In conclusion, although the exact timing and extent of a possible AMOC collapse are still debated, this study makes a significant contribution to understanding the potential, radical changes that could occur in Europe's climate. Spring