AGU: Geophysical Research Letters

 

Editors' Highlight

Natural ocean cycles will soon weaken thermohaline circulation

The Atlantic Multidecadal Oscillation (AMO) is a pattern of multidecadal surface temperature variability centered on the North Atlantic Ocean, seen in analyses of global climate using measurements dating back to the nineteenth century. Shown to have been linked with Sahel drought, Brazilian rainfall rates, North American climate, and Atlantic hurricane frequency, studies of these 50–100 year fluctuations are hindered by short global climate records and insufficient subsurface ocean data. Thus it is difficult to conclude whether the AMO is genuinely oscillatory. To clarify this, Knight et al. (2005) examined a 1400 year simulation that replicates the observed pattern and amplitude of the AMO. Their results imply that the AMO is a genuine quasiperiodic cycle related to the variability in the oceanic thermohaline circulation (THC). Using this relationship, they attempted to reconstruct past THC changes, and they observed an increase in THC strength over the last 25 years. Owing to the AMO's oscillatory nature the authors infer a decreasing THC strength over the next few decades, which would accelerate the anticipated anthropogenic weakening of the same phenomenon. They suggest that future climate change predictions need to account for natural changes expected from shifts in the AMO.

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