As global warming raises ocean levels worldwide, scientists have long warned that many low-lying coastal areas will be permanently submerged.
But a new study released Thursday reveals that much of the economic damage caused by rising sea levels in this century is likely to come from an additional threat that will come even faster: As the oceans rise, there will be strong coastal storms, waves and extreme tides. able to go further inland, putting tens of millions more people and billions of dollars in assets worldwide at risk of periodic flooding.
The study, published in the journal Scientific Reports, calculated that up to 171 million people living today face at least some risk of coastal flooding due to extreme high tides or storm surges, created when strong winds from hurricanes or other storms accumulate the ocean water and push ashore. While many people are currently protected by levees or other defenses, such as those in the Netherlands, not all are.
If nations of the world continue to emit greenhouse gases and sea levels rise just 1 to 2 feet more, the amount of coastal land at risk of flooding would increase by about a third, according to the research. In 2050, up to 204 million people currently living along the coasts would face flood risks. By 2100, that rises to up to 253 million people in a moderate emissions scenario known as RCP4.5. (The actual number of people at risk may vary, as the researchers did not attempt to predict future changes in the coastal population.)
“Despite the average sea level rising relatively slowly, we found that these other flood risks, such as high tides, storm surge, and breaking waves, will become much more frequent and intense,” said Ebru Kirezci, candidate for PhD at the University of Melbourne in Australia. and lead author of the study. “It is important to keep them in mind.”
Areas of particular risk include North Carolina, Virginia, and Maryland in the United States, northern France, and northern Germany, the southeast coast of China, Bangladesh, and the Indian states of West Bengal and Gujarat.
This flood could cause serious economic damage. The study found that people currently living in areas at risk from a 3-foot rise in sea level owned $ 14 trillion in assets in 2011, an amount equal to 20 percent of world GDP that year.
The authors acknowledge that theirs is a highly imperfect estimate of the potential costs of sea level rise. On the one hand, they do not take into account the likelihood that communities will take steps to protect themselves, such as raising their homes, building walls, or retreating inland.
The study also failed to account for any valuable infrastructure, such as roads or factories, that is at risk. A more complete financial accounting would require more investigation, Kireczi said.
There are already indications that periodic flooding is wreaking havoc on the coasts. A July analysis by the National Oceanic and Atmospheric Administration found that high-tide floods in cities along the Atlantic and the Gulf Coast have multiplied by five since 2000, a change that is damaging homes, endangering the drinking water supply and flooding roads.
The new study attempts to improve projections of future coastal flood risks by combining existing models of rising sea levels, tides, waves, storm surges, and coastal topography, while comparing those models to data collected from tide gauges. of all the world. Previous research, Kirezci said, had not analyzed factors such as breaking waves that can temporarily raise local sea levels in as much detail.
“Trying to model extreme sea levels and storm surge is an extremely complicated problem and there are still many uncertainties,” said Michael Oppenheimer, a climate scientist at Princeton University who was not involved in the study. But, he said, it was critical for scientists to develop good estimates, because if cities like Boston or New York hope to build new and expensive barriers against storm surges or other defenses, they will have to plan decades before the highest sea levels hit.
The new study found that only a third of future coastal flood risk came from sea level rise that would permanently submerge low-lying areas. Two-thirds of the risk comes from a likely increase in extreme high tides, storm surges, and breaking waves. In many coastal areas, the type of rare floods that historically occurred once every 100 years, on average, could occur every 10 years or less by the end of the century.
Scientists say nations of the world can greatly reduce future flood risks by reducing emissions rapidly, especially since that could reduce the chances of a rapid collapse of the Antarctic ice sheet that would raise ocean levels. even more than expected in the century.
But, added Dr. Oppenheimer, the world has become so heated that a significant sea level rise is guaranteed by 2050, no matter what happens to emissions. “That means we must also start preparing to adapt now,” he said.
