Are AMV Impacts Stable Throughout the 20th Century?

We examined the impact of two North Atlantic modes of climate variability, the Atlantic Multidecadal Variability (AMV) and the North Atlantic Oscillation (NAO), on observed surface temperature, pressure, and rainfall across the globe. The AMV is calculated from the average sea surface temperatures over the North Atlantic basin (0° to 60°N, 80°W to 0°). The NAO is calculated from the difference in pressure between the Azores high and the Icelandic low. We find a distinct negative correlation between the two climate modes in the early twentieth century, prior to 1950, when both the AMV and NAO were largely driven by internal atmospheric and oceanic dynamics and volcanic eruptions. The negative correlation is also evident in the patterns of temperature, pressure, and precipitation associated with each of these modes. Both the NAO- and AMV+ surface temperature patterns are particularly clear, with the US and northern Europe being cooler and southern Europe warmer. The atmospheric pressure patterns between the AMV+ and NAO- are also similar with lower pressure over southern Europe and the Azores and higher pressure over northern Europe and Iceland. However, after 1950 the surface temperature, pressure, and rainfall patterns associated with the AMV and NAO diverge. While the pattern of NAO impacts has remained largely unchanged, the AMV shifts from a NAO-like pattern to a pattern of warming temperatures globally with the most notable temperature increases over the US, Europe, and Asia. We hypothesize that the separation occurs due to an increase in anthropogenic forcing, namely from aerosols and greenhouse gases, which causes the two processes to move out of sync. This lack of correlation with the AMV suggests that AMV impacts around the globe are currently distinct from NAO impacts.