Recently, the research team led by Academician Wu Lixin from the Key Laboratory of Physical Oceanography/Frontier Science Centre for Deep Ocean Multispheres and Earth System has achieved a major breakthrough in climate change research. Their study, titled Intensified Atlantic multidecadal variability in a warming climate, was published in Nature Climate Change. The research reveals the spatiotemporal characteristics of enhanced amplitude and prolonged periodicity in Atlantic Multidecadal Variability (AMV) under global warming. Crucially, it identifies the thinning of the oceanic mixed layer and the cumulative effects of oceanic advective heat transport as key drivers of these changes.

The Atlantic Multidecadal Variability (AMV) refers to the basin-scale, multidecadal fluctuations of sea surface temperature (SST) anomalies over the North Atlantic. As one of the typical modes of global climate variability on decadal scales, it exerts significant impacts on the climate and fishery resources both regionally and globally. Currently, how global warming affects the intensity and mechanisms of AMV remains unclear, severely limiting our understanding of its associated climatic effects and impeding climate predictions on decadal scales. The Atlantic Meridional Overturning Circulation (AMOC), a critical component of the ocean thermohaline circulation, facilitates trans-basin meridional heat transport and plays a vital role in sustaining the AMV.

This study, based on multi-scenario and multi-model coupled atmosphere-ocean data from CMIP5/6, reveals that under global warming, the AMV exhibits enhanced amplitude and an extended period in its spatiotemporal evolution (Figures 1a, b). This is due, in part, to the melting of sea ice under global warming, which increases freshwater flux and surface heat flux. These increased fluxes suppress deep ocean convection in the subpolar North Atlantic, leading to a sharp decrease in the depth of the oceanic mixed layer (Figure 1c). With a shallower mixed layer, the reduced ocean heat capacity makes SST more sensitive to heat flux perturbations, thus enhancing the AMV amplitude. Furthermore, the weakening of deep convection also slows down the Atlantic Meridional Overturning Circulation (AMOC) and its associated northward heat transport. This extended accumulation time for SST anomalies promotes further enhancement of the AMV amplitude (Figure 1d).

The research suggests that future global climate variability on multidecadal timescales, and associated extreme climatic events may intensify in a warming climate. This provides a critical theoretical basis for climate predictions on decadal timescales.