Palm Trees Growing in Ireland

A paper from 2018 describes the mechanism and the possibility of the transfer warmth to Ireland coming to an end.

A warming deficit in North Atlantic sea surface temperatures is a striking feature in global climate model future projections. This North Atlantic warming hole has been related to a slowing of the Atlantic meridional overturning circulation (AMOC); however, the detailed mechanisms involved in its generation remain an open question. An analysis of the Community Earth System Model Large Ensemble simulations is conducted to obtain further insight into the development of the warming hole and its relationship to the AMOC. It is shown that increasing freshwater fluxes through the Arctic gates lead to surface freshening and reduced Labrador Sea deep convection, which in turn act to cool Labrador Sea sea surface temperatures. Furthermore, the resulting changes in surface ocean circulation lead to enhanced transport of cooled Labrador Sea surface waters into the interior of the subpolar gyre and a more zonal orientation of the North Atlantic Current. As a result, there is an increase in ocean advective heat flux divergence within the center of the subpolar gyre, causing this warming deficit in North Atlantic sea surface temperatures. These local changes to the ocean circulation affect the AMOC and lead to its slowdown.

Abstract

The Atlantic meridional overturning circulation (AMOC)—a system of ocean currents in the North Atlantic—has a major impact on climate, yet its evolution during the industrial era is poorly known owing to a lack of direct current measurements. Here we provide evidence for a weakening of the AMOC by about 3 ± 1 sverdrups (around 15 per cent) since the mid-twentieth century. This weakening is revealed by a characteristic spatial and seasonal sea-surface temperature ‘fingerprint’—consisting of a pattern of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region—and is calibrated through an ensemble of model simulations from the CMIP5 project. We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport, as well as an associated northward shift of the Gulf Stream. Comparisons with recent direct measurements from the RAPID project and several other studies provide a consistent depiction of record-low AMOC values in recent years.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JC022651 Physics-Based Indicators for the Onset of an AMOC Collapse Under Climate Change René M. van Westen, Elian Vanderborght, Michael Kliphuis, Henk A. Dijkstra First published: 24 August 2025 https://doi.org/10.1029/2025JC022651

Abstract

The Atlantic meridional overturning circulation (AMOC) is an important tipping element in the climate system. There is a large uncertainty whether the AMOC will start to collapse during the 21st century under future climate change, as this requires long climate model simulations which are not always available. Here, we analyze targeted climate model simulations done with the Community Earth System Model (CESM) with the aim to develop a physics-based indicator for the onset of an AMOC tipping event. This indicator is diagnosed from the surface buoyancy fluxes over the North Atlantic Ocean and is performing successfully under quasi-equilibrium freshwater forcing, freshwater pulse forcing, climate change scenarios, and for different climate models. An analysis consisting of 25 different climate models shows that the AMOC could begin to collapse by 2063 (from 2026 to 2095, to 25th to 57th percentiles) under an intermediate emission scenario (SSP2-4.5), or by 2055 (from 2023 to 2076, to 25th to 75th percentiles) under a high-end emission scenario (SSP5-8.5). When the AMOC collapses, the Northwestern European climate changes drastically and this will likely induce severe societal impacts.

Plain Language Summary

There is a growing risk that the Atlantic meridional overturning circulation (AMOC) collapses to a significantly weaker state under climate change. This AMOC tipping event causes a substantial shift of the global climate. It is therefore important to assess the risk of such an event under future climate change, but this requires long climate model simulations which are not always available. We developed a robust indicator that accurately predicts the onset of an AMOC tipping event and works under different forcing configurations and for different climate model simulations. Under a high-emission scenario (SSP5-8.5), the likelihood of an AMOC tipping event occurring in the 21st century is high and reduces for lower emission scenarios (SSP2-4.5). If the AMOC starts to collapse, it takes more than 100 years to reach a substantially weaker state. During that transition, the Northwestern European climate would change drastically and is expected to see colder winters, less rainfall, and more severe winter storms.

Key Points

• Multiple AMOC collapses are simulated in the CESM under transient climate change scenarios
• A physics-based indicator derived from surface buoyancy fluxes is proposed for the onset of an AMOC collapse under transient forcing
• The indicator is successfully performing in CESM freshwater pulse and climate change simulations, including CMIP6 under climate change