1. Introduction

The Atlantic Meridional Overturning Circulation (AMOC) is a large-scale circulation of the Atlantic Ocean that shapes the global and regional climate by redistributing heat across latitudes (Buckley and Marshall, 2016). This system of currents will slow down due to anthropogenic climate change (Weijer et al., 2020; IPCC 2021; Madan et al., 2023; Bonan et al., 2025), and there is a risk that this slowdown could be both more substantial and occur within a few decades, if there is transition of AMOC to another stable state that involves a severely weaker circulation than at present (Stommel, 1961; Rahmstorf 1996, van Westen et al. 2025b). Such a transition could happen if the AMOC surpasses a critical forcing level or climate state threshold, a so-called tipping point (van Westen et al., 2024), with the likelihood of AMOC collapse increasing as global warming progresses (Armstrong-McKay et al. 2022; Möller et al., 2024; Drijfhout et al. 2025; van Westen et al. 2025a; Shin et al. preprint). Several recent studies suggests that the tipping point which starts an AMOC shutdown could occur before 2100 (Rahmstorf, 2024; Ditlevsen & Ditlevsen, 2023; van Westen et al., 2025a; Boers, 2021, Drijfhout et al. 2025). However, it remains unclear how fast a collapse would unfold after crossing such a tipping point, with a timescale ranging from 15 to 300 years (Armstrong McKay et al., 2022).

The impacts of such a collapse in Northern Europe depend on the global warming level at which the collapse occurs. If the transition is more sensitive to global temperature than is currently predicted (taking place around ~2°C warming level with respect to preindustrial), it could result in net cooling in northwest Europe (Romanou et al., 2023; Boot et al., 2024; van Westen & Baatsen, 2025), regulated by the degree of sea ice expansion (Bellomo and Mehling, 2024); at higher warming levels, net cooling becomes less likely. However, other impacts, such as North Atlantic sea-level rise, warming of the southern hemisphere, and a southward shift of the tropical rain belt (intertropical convergence zone – ITCZ), are independent of background global warming and will accompany any AMOC slowdown (IPCC, 2021).

Based on the scientific understanding at the time, the IPCC (2021) assessed that AMOC is unlikely to undergo abrupt changes before 2100, but would have serious consequences if it were to occur. However, a recent letter to the Nordic Council of Ministers – endorsed by 44 climate scientists – argued that the risk has been underestimated and that the outcomes of an AMOC collapse could bring “irreversible impacts, especially for Nordic countries” (Rahmstorf et al., 2024).

Using data from the latest model generation (38 CMIP6 models with over 768 simulations), Drijfhout et al. (2025) found that in most models the AMOC starts to weaken in the late 20th century and weakens substantially through the 21st century, reaching an essentially shutdown state in the 22nd century in many of the simulations that continue beyond 2100. Overall, they estimate a probability of an AMOC shutdown of 70% for high emissions, 37% for intermediate emissions and 25% for low emissions - making it a credible risk. However, the probability and timing of passing the AMOC tipping point are very difficult to predict.

Continuous direct measurements of AMOC strength are available only since April 2004 (RAPID Array) and show a statistically significant weakening trend (-0.8 ± 0.7 million cubic meters per second per decade; Volkov et al. 2024). Due to the short time series, attributing the trend to a forcing is difficult - it could be due to natural variability and/or to climate change. However, the trend is consistent in magnitude with model simulations that ultimately lead to an AMOC shutdown (Drijfhout et al. 2025) and many indirect estimates of AMOC strength over the historical period (Dima and Lohmann 2010, Drijfhout et al. 2012, Rahmstorf et al. 2015, Caesar et al. 2018, Zhu & Liu 2020, Chafik et al. 2022, Rossby et al., 2022, Qasmi 2023, Li & Liu 2025, Ren et al. 2025, Michel et al., 2025) and the Holocene (Caesar et al. 2021, 2022) suggest a long term AMOC slowdown consistent with global warming contributing to it.

Given the possibility of an AMOC shutdown, the authors of this report suggest Nordic societies to recognize it as a serious risk which requires a dedicated risk management framework to manage its environmental and societal impacts. We have such existing frameworks for other risks, such as geohazards (earthquakes, tsunamis, asteroid impacts, tropical storms, floods, etc.), which would generally not have as widespread impacts as AMOC shutdown. A key to an AMOC collapse risk management framework is identifying its possible impacts on people and natural ecosystems along with drafting mitigation and adaptation plans. In this report we provide an initial look at possible frameworks, identify existing knowledge gaps, and suggest further actions.

The rest of the report is organized into four sections. Section 2 examines the impacts of an abrupt AMOC collapse. Section 3 lays out possible mitigation and adaptation strategies. Section 4 discusses the possible emphasizes identifying key knowledge gaps and highlights priorities for future research and Section 5 provides key action points for the Nordic countries.

Figure 1 Schematic representation of the main impacts of an AMOC collapse on the physical climate system. The background shading shows the climatological February mean sea surface temperature in blue to yellow hues, and minimum sea ice concentration on white to gray hues. The gray lines show the minimum (solid) and maximum (dashed) of local sea ice extent based on satellite observations (OI-SST, 1982–2025) in the North Atlantic. Potential consequences of an AMOC collapse on the physical climate system in the region of the North Atlantic include: (1) sea ice expansion (2) sea surface temperature decrease/displacement of ocean fronts (3) sea level rise (4) changes in mid-latitude cyclones (5) air temperature decrease. Figure credit: FMI, Aleksi Nummelin.