On the coasts of the conterminous USA, climate-induced sea levels are rising faster than the global average 3, with an expected increase over the next few decades (Fig. As sea level rises and land subsides, the hazards associated with climate extremes (for example, hurricanes and storm surges), shoreline erosion and inundation of low-lying coastal areas grow 21, 22. In this study, we refer to SLR that incorporates the effects of vertical land motion (VLM) as ‘relative SLR’, whereas ‘geocentric SLR’ refers to SLR without VLM.
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Furthermore, coastal cities often experience sinking land (so-called land subsidence), whose compounding effect contributes to relative SLR, exacerbating coastal hazards and risks 2, 5, 19, 20. Even if climate change mitigation efforts succeed in stabilizing temperature in the future decades, sea levels will continue to rise as a result of the continuing response of oceans to past warming 3, 17, 18. Global mean sea level has risen by about 0.17 m over the past 100 years, with global rates of SLR accelerating from about 1.7 mm per year in the late twentieth century to about 3.1 mm per year in the early twenty-first century in response to warming temperatures 3, 15, 16, 17 and is 3.7 mm per year at present (ref. Globally, SLR will pose a substantial socioeconomic challenge in the twenty-first century, primarily affecting human populations, infrastructure and ecosystems along major coastlines 10, 11, 12, 13, 14. Climate change is already causing an increase in the frequency and intensity of heatwaves, hurricanes and wildfires and severely affecting the world’s freshwater resources through sea-level rise (SLR), more frequent droughts and changes in precipitation and evapotranspiration 6, 7, 8, and these effects will almost certainly grow in the future 9. The widespread consequences of global climate change stress human communities and ecosystems worldwide. These potential consequences show the scale of the adaptation challenge, which is not appreciated in most US coastal cities.
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Our analysis shows that not accounting for spatially variable land subsidence within the cities may lead to inaccurate projections of expected exposure. Here we show that, even when considering the current coastal-defence structures, further land area of between 1,006 and 1,389 km 2 is threatened by relative sea-level rise by 2050, posing a threat to a population of 55,000–273,000 people and 31,000–171,000 properties. In this study, we combine high-resolution vertical land motion (that is, raising or lowering of land) and elevation datasets with projections of sea-level rise to quantify the potential inundated areas in 32 major US coastal cities. However, these impacts may be exacerbated by coastal subsidence-the sinking of coastal land areas 4-a factor that is often underrepresented in coastal-management policies and long-term urban planning 2, 5.
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The sea level along the US coastlines is projected to rise by 0.25–0.3 m by 2050, increasing the probability of more destructive flooding and inundation in major cities 1, 2, 3.