Scientists at Climate Central, a New Jersey-based research center, have published a new model for estimating coastal elevations, which predicts that the effects of sea-level rise could be three times more severe than previous estimates. Under these new models, as many as 340 million people will live below annual flood levels by 2050. By the end of the century, land currently occupied by 190 million people will be below high-tide levels, assuming the lowest levels of carbon emission. The results of this new model have immense scientific, geopolitical, and economic implications.
Publishing late last month in Nature Communications, computational scientist Scott Culp and ecologist Benjamin Strauss introduced a new, substantially more accurate method for finding the elevation of land in coastal areas. Using global satellite-based elevation data, along with airplane LIDAR of coastal regions of the United States, the authors trained a neural network to correct for obstacles such as buildings and trees that can impede a satellite’s vision of the ground. They found that previous satellite models, which had not used machine learning, substantially overestimated the safety of many coastal areas. Remarkably, the best-case scenarios under the new model (named CoastalDEM 1.1) are worse than the worst-case scenarios under old models.
These results have an exceptionally high degree of urgency for cities in Asia, where a dangerous conjunction of inaccurate mapping and low-lying coastal population centers puts millions of people at increased risk. More than one-quarter of the population of Vietnam (20 million people) is estimated to live below high tide levels by 2100. Substantial portions of Bangkok, Mumbai, Jakarta, the Pearl River Delta, and coastal Bangladesh will also be inundated. The effects aren’t limited to Asia, however. CoastalDEM also places Basra (Iraq) and Alexandria (Egypt) underwater. Notably, these effects will occur even under the most conservative estimates of sea-level rise, underscoring the serious inaccuracy of previous predictions.
There will be two primary effects of this worsened flooding. First, in areas that can afford it, enormous expenditures will be necessary to construct seawalls, dikes, levees, and flood control infrastructure. The impact on economic productivity from these constructions could be severe. Notably, CoastalDEM shows that 110 million people already live below high tide levels, in population centers like Amsterdam and Shanghai. This resistance to increasing sea levels is possible thanks to technological innovations that protect populated areas from flooding. However, flood control can fail. Speaking to the New York Times, Strauss pointed to the effects of Hurricane Katrina, which overwhelmed New Orleans’s levee system and killed almost 2,000 people. The question, he told the Times, is “How deep a bowl do we want to live in?”
Second, in areas where billion-dollar flood control efforts are not feasible (likely the majority of inundated areas), a new refugee crisis could emerge. Escaping from inadequate infrastructure and increasing natural disasters, coastal dwellers around the world may begin to move inland, potentially overwhelming the capacity of inland communities. Climate refugees will become an increasing share of the global migration crisis, compounding previous geopolitical stress, adding new regions of concern, and extending the current surge of migration into the 2100s.
In the 20th century, sea levels rose by 11-16 cm globally, almost entirely attributable to climate change. In the 21st century, there are concerns that the Antarctic ice sheet may begin to destabilize under rising temperatures, potentially leading to increases in sea levels as large as 2 meters. However, even without this contribution from the southern ice cap, sea-level rise will still reach as much as 50 cm by 2100 under the most optimistic carbon emission estimates.
Climate change is a preeminent threat to global security, economic productivity, and development. This surprising new model, which points to an increased effect for just one aspect of climate change—sea level—underscores the urgency of climate action and the risk of continued irresolution.
This article is based on the paperKulp, S.A., Strauss, B.H. New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nat Commun10, 4844 (2019) doi:10.1038/s41467-019-12808-z. Climate Central also provides a very helpful visualization tool on their website, which is available at coastal.climatecentral.org.