Estimated linear least squares trends in annual mean sea-level pressure from 1900 to 2012 from three datasets: (from left to right): National Center for Atmospheric Research (NCAR), National Oceanic and Atmospheric Administration 20^th Century analysis (20CR), 20^th century reanalysis and Hadley Centre Sea Level Pressure (HADSLP2)Hadley Centre analysis. Trends are reported in units of millibars per century. For reference, an x is placed over the center of action of the mode of variability reported by JM.