Abstract
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. A distinct negative correlation was found between the two climate modes in the early twentieth century, prior to 1950, when anthropogenic forcing was less significant. Both the pre-1950 AMV+ and NAO- 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 diverged. This shift in patterns can help to explain long-term trends in climate that people are experiencing around the world, particularly during the Northern Hemisphere winter. While the pattern of NAO impacts has remained largely unchanged, the AMV shifts from an 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.