evidence: Taking extreme value analysis as an example, the rule of thumb is that extrapolation of extreme water level events should be limited to return periods not longer than four times the available record length4. This means in order to derive an estimate of the 100-year storm surge level, at least 25 years of data are needed (to derive a 500-year event, 125 years of data would be needed). However, tide gauge records, which are the main data source for storm surge information, often cover much shorter time periods. From the global dataset of extreme sea level observations we used, 45% of the 882 tide gauges included in this study have less than 25 years of data. Moreover, analyzing long-term trends and multi-decadal variability in the storm surge climate is also hampered by short record lengths. To assess the long-term trend in global mean sea level it has been estimated, for example, that a minimum of 60 years of data are required5, which is the case for only 12% of the tide gauges analyzed here; given the larger variability, even longer records are needed to reliably explore long-term changes in the storm surge climate.