Record heat waves and wildfires singed states this past summer, awakening Americans to a warming globe. As the earth’s climate continues to change, risk must be predicted further in advance to anticipate increasingly severe weather. Hurricanes are one such concern. Hurricane floods so violent they occur only once a century now could hit low-lying coastal areas every one or two decades.
The Woodrow Wilson School’s Michael Oppenheimer, Albert G. Milbank Professor of Geosciences and International Affairs, and other climate scientists at Princeton and the Massachusetts Institute of Technology, combined models that project broad climate changes decades into the future with those that simulate storm development, generating 45,000 synthetic storm events under various climate conditions.
Ning Lin, Ph.D. ’10, assistant professor of civil and environmental engineering at Princeton, is lead author on the study, “Physically Based Assessment of Hurricane Surge Threat Under Climate Change,” published online in Nature Climate Change (Feb.14, 2012). The study demonstrates potential effects of global warming on storm surges — among the deadliest and most destructive forces endured during landfalling hurricanes. Hurricane Katrina’s surges in 2005, which marked the highest coastal flood heights ever recorded in the U.S., produced the country’s costliest natural disaster. Previous studies have targeted the effect of global warming on storm climatology generally, but not on surge events in particular.
Monitoring their algorithmic models, the researchers note synthetic surges slamming into the Battery, at the southern tip of Manhattan. A dense population, putting more people and money at risk, and its considerable prior exposure to hurricanes made New York City an illustrative case study.
The existing seawall safeguarding lower Manhattan renders the city “highly vulnerable” even to present flooding threats, the study warns. Extending roughly 1.5 meters above sea level, the seawall could be swallowed by a severe surge of 2.03 meters that occurs every 100 years, one of 3.12 meters every 500 years. Global warming could augment these threats by hastening sea level rise and affecting storm climatology, the researchers found. By the end of the century, such extreme surge tide levels could impact land as often as once every 20 years, or every 240 years, respectively.
And these kinds of predictions are not limited to New York City; the study's methods could be applied to other locales. As Oppenheimer explained, the methods could be used “to infer the change in likelihood that such a storm would affect various regions in the future as the Earth warms and sea level rises.” The innovative “computationally efficient” method was intended to be easily replicable.
Such pliability is a boon to coastal planners, who can apply these risk assessments toward expedient coastal protections. “One of our objectives was to provide information in a form that decision makers are able to understand,” Oppenheimer said, “so that they are able to implement policies on that basis. It’s ‘news you can use,’ so to speak.”
Seawalls, jetties, and other ‘hard’ protective measures will be required, Oppenheimer explained, but should be used in combination with ‘soft’ tactics such as wetland restoration, flood-zone population reduction and architectural reinforcement, which he sees as ultimately more promising.
“The whole idea is to make people think more carefully about coastal planning, and to reduce risk by taking certain measures,” Oppenheimer said. “In my view, the major advance here, and with respect to global warming in general, is that scientists are starting to take advantage of statistical methods to capture risk.”
“This work is exploding all over the place,” Oppenheimer observed. “Every region faces some threat or enhanced risk due to climate change, and the specifics will differ from place to place.” In other words, studying storms is only the beginning. “We need more of this work, not just on hurricanes but across the range of risks facing humans,” he said.
Some amount of warming, to be sure, is inevitable. But Oppenheimer is confident that we can address the underlying cause by reducing greenhouse gas emissions and, in the meantime, mitigate risk.
At Princeton, Oppenheimer is pushing to equip the next generation of environmental scientists with the requisite policy expertise. He directs a program offered by the Princeton Environmental Institute in affiliation with the Woodrow Wilson School: a two-year fellowship program in science, technology, and environmental policy. PEI-STEP creates opportunities for doctoral students in science and engineering to analyze policy implications in their fields, prompting some graduates to pursue careers in government.
Asked how these teaching and research efforts might reduce regional vulnerabilities, Oppenheimer conceded that only time will tell. “How do individuals and governments react when given such information? Under what circumstances do they act upon it?” If his latest findings are any indication, we may not be waiting long to find out.
An earlier version of this article appeared on the homepage of the Woodrow Wilson School at Princeton.