AMOC Stability Depends on Warming Rate, Not Temperature
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- René van Westen at the University of Utrecht led the study, simulating AMOC stability under three CO2-increase rates: 0.5 ppm/year, five times that, and 10 times that — the fastest comparable to today's pace.
- The AMOC remained stable past 5°C of warming under the slowest scenario, but collapsed at roughly 2°C of warming under current rates, something van Westen called "very surprising."
- Van Westen said the AMOC's stability is "not controlled by some magical temperature level" but by how fast the climate is warming — under fast warming, surface waters lose density faster than deep waters, stratifying the ocean.
- Without the AMOC, much of Europe would suffer a 10–30°C drop in wintertime temperatures, and global rainfall patterns would shift with catastrophic consequences, the study notes.
- David Armstrong McKay at the University of Sussex cautioned that higher-complexity models vary in AMOC behavior and carry biases, so this can't yet be taken as "a clear-cut, real-world projection."
- Camille Hankel at the University of Washington argued that slowing the rate of CO2 increase "immediately" may be more crucial for averting AMOC weakening than limiting the total amount of CO2 emitted.
Why it matters: For policymakers, the finding reframes the climate goal: slowing the rate of emissions may matter as much as reaching net-zero, since today's pace of warming could collapse the AMOC by around 2060 at just 2°C — while slow warming would preserve it past 5°C. But external experts caution the model omits Greenland ice-sheet melt and methane, so it's not yet a clear-cut real-world projection.
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