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Long-Term Climate Simulations Indicate That the Collapse of the Atlantic Meridional Overturning Circulation May Persistently Increase the Intensity of Summer Droughts in Europe, With More Severe Effects in the South of the Continent and Impacts That Could Last for Up to a Thousand Years
A new study indicates that the collapse of the Atlantic Meridional Overturning Circulation may amplify extreme droughts and prolong dry spells in Europe for up to 1,000 years, with more severe impacts in the south of the continent, according to long-term simulations with different climate scenarios.
The Role of the Atlantic Meridional Overturning Circulation in European Climate
The Atlantic Meridional Overturning Circulation is an ocean current system that transports heat from the Southern Hemisphere to the Northern Hemisphere and plays a central role in regulating global climate. This mechanism helps explain why Northwestern Europe has a milder climate compared to regions in southern Canada at the same latitude.
In addition to influencing temperatures, the circulation also aids in the transport of moisture toward the European continent. According to researcher René van Westen, the combination of temperature and precipitation is crucial for regional climate.
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A potential collapse of the system would result in much colder winters and significant changes in precipitation patterns.
Scientists have already warned that human-caused climate change is weakening this ocean current system.
The risk would be associated with the approach of tipping points, defined as critical thresholds in the Earth’s climate system, beyond which abrupt and lasting changes may occur.
Climate Simulations and Scenarios Analyzed in the Study
The study conducted eight climate simulations that extended over more than 1,000 years, aiming to compare the effects on summer precipitation in Europe should the Atlantic circulation collapse. Four simulations replicated pre-industrial levels of greenhouse gases, considered theoretical since those levels have already been exceeded.
Two other simulations adopted the RCP4.5 scenario, in which carbon emissions peak in the middle of the century and then start to decline. In this set, the researchers assessed the effects of small and large amounts of freshwater being dumped into the Atlantic, a condition associated with the melting of polar ice caps.
When large volumes of freshwater altered the salinity and density of the ocean, circulation collapsed. In scenarios with lower freshwater input, the system managed to recover. The last two simulations modeled a high emissions scenario, RCP8.5, with carbon emissions three times higher than current levels, leading to a collapse of circulation in both analyzed cases.
Van Westen highlighted that the two RCP4.5 scenarios are considered the most realistic among the eight simulated. According to him, climate change is already tending to intensify evaporation and make dry spells even drier, and the collapse of circulation would exacerbate this process significantly.
Projected Impacts on Droughts and Precipitation in Europe
The results show that, across Europe, the intensity of the dry season increases by 8% in an RCP4.5 scenario with intact Atlantic circulation. Should a collapse occur, this increase reaches 28%, indicating a significant amplification of aridity conditions during the summer.
The study also points to stark contrasts between the north and south of the continent. In Sweden, the dry season increases by 54% with active circulation and 72% without it. In Spain, which is already facing extreme drought, there would be a 40% increase in the dry season with the system intact and a 60% increase in the collapse scenario.
These numbers reflect stable climate states, analyzed after hundreds of years, and not the current phase of accelerated warming. According to the authors, the aim was to identify average climate responses in Europe under different background states of ocean circulation, allowing for the assessment of persistent impacts over time.
The study suggests that even in moderate mitigation scenarios, the collapse of circulation could significantly transform the European water regime, with prolonged and difficult-to-reverse effects. The analysis indicates that these changes would not be temporary but would persist for centuries.
Independent Evaluations and Limits of Theoretical Projections
Climate scientist Karsten Haustein praised the long-term approach taken by the study. According to him, the simulations analyze conditions hundreds of years after the initial changes, offering a different perspective from the transitional scenarios generally used to plan the coming decades.
Haustein noted that equilibrium scenarios should not be confused with projections for the next 50 or 100 years. Very dry conditions over shorter periods may not last indefinitely, depending on the evolution of emissions and the behavior of the climate system as a whole.
Professor Jon Robson warned about limitations of the model used. According to him, for the collapse to occur in the simulations, it is necessary to add large amounts of freshwater to the North Atlantic, which would not be realistic under current conditions, though it serves as a warning for extreme scenarios.
For Stefan Rahmstorf, the overall message of the study is clear. The drought problems already expected due to global warming would be worsened by a significant weakening of the Atlantic circulation, a risk that, according to him, seems increasingly likely.
Rahmstorf stressed that any potential shutdown of the system would have consequences for at least a thousand years, representing a long-term responsibility for today’s decision-makers.
The conclusions reinforce that present choices could influence European climate for generations, amplifying risks of extreme drought and lasting water instability, with profound impacts on societies and ecosystems over time, even if the scenario is theoretical in some models and depends on extreme conditions to materialize.
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