Changes in cloud cover over Europe and the North Atlantic have been observed to be a significant driver of sunshine duration (SD) changes, and thus climate change, in this region. Changes in cloud cover are “the result of internal variability in the ocean-atmosphere system.”
Previously, the non-linear, oscillatory climate variations over Europe had been assumed to be connected to the sunshine duration variations elicited by anthropogenic pollution (aerosol) mitigation policies.
But a new study (Marsz et al., 2023) presents compelling evidence decadal-scale sunshine duration variations are driven by the internal processes affecting cloud cover, namely the natural thermohaline circulation in the North Atlantic (THC NA). This relationship spans the entire period from 1900 to 2018.
“The mechanisms of the THC NA functioning are known and indicate that they are the result of the internal variability in the ocean-atmosphere system.”
“SST changes occur not only because of changes in the amount of radiation reaching the ocean’s surface but also due to the meridonal oceanic heat transport.”
“[I]t is the long-term changes in the thermal condition of the North Atlantic, and not changes in the concentration of aerosols, that would be the primary cause of the long-term change in the SD over Europe.”
“[T]he occurrence of long-term variability in the SD over Europe, manifested in the occurrence of successive phases of dimming and brightening, can be explained without resorting to changes in the concentration of volcanic and anthropogenic aerosols in the atmosphere.”