Fewer large waves for eastern Australia

For about 36 days each year, Australia’s east coast is battered by storms whose waves top 4 meters. That average rate, which pertains to 1992–2010, was derived from meteorological data. How the number of such storms could change as Earth’s climate warms is the subject of a new computational study led by Andrew Dowdy of Australia’s Bureau of Meteorology. Because climate models do not directly predict wave activity, Dowdy first had to identify a proxy. Large waves on the east coast are typically caused by midlatitude cyclones (like the example in the figure) that develop over the Pacific Ocean. Dowdy found that the occurrence of large waves is strongly related to the curvature of the region’s atmospheric pressure contours—specifically, of the height above mean sea level at which the pressure is 500 hectopascals (0.49 atm). He and his team ran 18 different models for the years 2006–2100 under two scenarios: By 2100, greenhouse gas concentrations could be about 50% higher than today (the realistic scenario) or risen to about three times the current levels (the pessimistic scenario). All the models predicted a decrease in the annual number of large-wave days. For the realistic scenario, the all-model average fell to 27 days by the year 2100; for the pessimistic scenario, it fell by 2100 to 22 days. The physical origin of the decrease is uncertain, as is the likely economic impact. On the one hand, large waves exacerbate the damage caused by rising sea levels. On the other, the waves attract money-spending surfers. (A. J. Dowdy et al., Nat. Clim. Change 4, 283, 2014, doi:10.1038/nclimate2142 .)