A signature of persistent natural thermohaline circulation cycles in observed climate

TLDR

It is unclear whether observed multidecadal temperature fluctuations are truly oscillatory based solely on the limited observational record. The study seeks to reconstruct past thermohaline circulation changes and infer a recent increase in THC strength over the last 25 years. A 1400‑year climate model simulation reproduces the observed AMO pattern and amplitude. 19th‑century climate data show the Atlantic Multidecadal Oscillation as a dominant multidecadal temperature pattern, and model results indicate it is a genuine quasi‑periodic cycle linked to thermohaline circulation, suggesting natural THC and AMO decreases in the coming decades independent of anthropogenic change.

Abstract

Analyses of global climate from measurements dating back to the nineteenth century show an ‘Atlantic Multidecadal Oscillation’ (AMO) as a leading large‐scale pattern of multidecadal variability in surface temperature. Yet it is not possible to determine whether these fluctuations are genuinely oscillatory from the relatively short observational record alone. Using a 1400 year climate model calculation, we are able to simulate the observed pattern and amplitude of the AMO. The results imply the AMO is a genuine quasi‐periodic cycle of internal climate variability persisting for many centuries, and is related to variability in the oceanic thermohaline circulation (THC). This relationship suggests we can attempt to reconstruct past THC changes, and we infer an increase in THC strength over the last 25 years. Potential predictability associated with the mode implies natural THC and AMO decreases over the next few decades independent of anthropogenic climate change.