Fig. 4: Changes in modes of climate variability during the last millennium.
Palaeoclimate reconstructions and instrumental data are shown for central-Pacific El Niño event numbers65, positive IOD event numbers53, and the summer SAM Index relative to the 1961–1990 mean66 (thin lines are annual summer SAM values; thick lines are 30-year running means). Note inverted y-axis for SAM Index so that the upward direction for each plot is toward more fire-promoting conditions in southeast Australia (Fig. 3). The increasing frequency of central-Pacific-type El Niño events and of positive IOD events in recent decades mean that these fire-promoting phases are now occurring more often than any other time in the last several centuries. Positive trends in the summer SAM in the twentieth century have moved this mode away from its fire-promoting phase, but this trend has paused in the past two decades due to ozone recovery68.
