This global screening study makes a first estimate of the exposure of the world's large port cities to coastal flooding due to storm surge and damage due to high winds. This study also investigates how climate change is likely to impact each port city's exposure to coastal flooding by the 2070s, alongside subsidence and population growth and urbanisation. The assessment provides a much more comprehensive analysis than earlier studies, focussing on the 136 port cities around the world that have more than one million inhabitants.