Analysis of Atlantic Meridional Overturning Circulation Transport Trends

The following report examines the observed decline in the Atlantic Meridional Overturning Circulation (AMOC).

The primary data for this analysis is derived from the RAPID array at 26N, covering a 20-year period from 2004 to 2023. This longitudinal record shows a decline in AMOC transport of approximately -1.19 Sv/decade, with a statistical significance of p=0.000822. This trend is supported by independent studies, including McCarthy et al. 2025, which reports a trend of -1.0 Sv/decade (90% confidence interval: -0.4 to -1.6) using deseasonalized monthly data. Further evidence for stability loss is provided by Boers 2021, while statistical early warning signals for a tipping point are noted in Ditlevsen 2023 and Westen 2024.

However, the quantitative trend is subject to significant measurement uncertainty. The entire trend rests on a single measurement array, and Volkov 2024 demonstrated that a correction to the Florida Current transport alone reduces the trend by approximately 40%, bringing it to the level of marginal significance. A second correction of a similar magnitude would eliminate statistical significance entirely. The 20-year RAPID record is shorter than the multi-decadal variability cycles found in paleoclimate proxies. Consequently, the observed decline could represent a phase of natural variability rather than a forced decline, as no pre-industrial baseline exists at this resolution to distinguish the two.

The causal mechanism chain - linking Greenland melt to freshwater input, density reduction, and AMOC weakening - remains a subject of investigation. While the Greenland freshwater link is plausible, observational studies suggest that deep convection in the Labrador Sea, the primary AMOC pump, is more sensitive to local wind patterns and the North Atlantic Oscillation (NAO) phase.

The potential consequences of an abrupt collapse, such as 3-8C European cooling, are derived from abrupt collapse scenarios in climate models rather than gradual weakening scenarios. A slow weakening at current rates would produce a much smaller warming offset of approximately 0.5-1.5C. The Ditlevsen 2023 tipping point window of 2025-2095 is a 70-year range; the model cannot distinguish between a tipping event occurring in 5 years or 75 years. This makes the confirmed status a statement of direction rather than urgency.

Finally, there is a critical gap in risk management. While the mechanism chain suggests potential for agricultural crisis and monsoon disruption, there is currently zero actuarial coverage in catastrophe bonds or reinsurance models for an AMOC collapse scenario.