Monitoring and Understanding Changes in Extremes: Extratropical Storms, Winds, and Waves

This scientific assessment examines changes in three climate extremes (extratropical storms, winds, and waves), with an emphasis on U.S. coastal regions during the boreal winter. There is evidence of an increase in both extratropical storm frequency and intensity in the Northern Hemisphere winter since 1950, with limited evidence of geographic shifts resulting in slight upward trends in off-shore/coastal regions. There is suggestive evidence of an increase in extreme winds (at least annually) over parts of the ocean during the past few decades, but the evidence over the U.S. land surface inconclusive. Finally, there is moderate evidence of an increase in extreme waves in winter along the Pacific coast since the 1950s, but along other U.S. shorelines any tendencies are of modest magnitude compared with historical variability. The data for extratropical cyclones are considered to be of relatively high quality for trend detection whereas the data for extreme winds and waves are judged to be of intermediate quality. In terms of physical causes leading to multidecadal changes, the level of understanding for both extratropical storms and extreme winds is considered to be relatively low while that for extreme waves is judged to be intermediate. Since the ability to measure these changes with some confidence is relatively recent, understanding is expected to improve in the future with the advancement of “climate reanalysis” projects.