Cleanup after Hurricane Sandy has proven costly for New York City – and climate change increases the odds of future flooding, say scientists. Photograph: Justin Lane/EPA
A new study published in the journal Nature Climate Change identifies a triple threat to America's coastal cities. This trio of phenomenon - sea-level rise, storm surges, and heavy rainfall will increase the threat to residents and infrastructure. Steven Meyers, a scientist at the University of South Florida and one of the authors is quoted as saying “What this shows is that there is an increasing risk of compound flooding, from storm surge and rainfall at the same time.”
We already know the rapid melting of the Greenland and Antarctica ice sheets are already raising sea level. In fact just a few day NASA reported that the glacier face in Greenland's fjords are deeper than thought and are being seriously eroded by ocean water near the sea floor. If all the ice melts in Greenland it could raise sea levels 21 feet. I wrote a diary regarding this news here. James Hansen took the unprecedented step of publishing a study prior to peer review as a stark warning to those meeting in Paris that urgent and drastic action is needed now.
Hansen’s study does not attempt to predict the precise timing of the feedback loop, only that it is “likely” to occur this century. The implications are mindboggling: In the study’s likely scenario, New York City—and every other coastal city on the planet—may only have a few more decades of habitability left. That dire prediction, in Hansen’s view, requires “emergency cooperation among nations.” We conclude that continued high emissions will make multi-meter sea level rise practically unavoidable and likely to occur this century. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization. The Guardian elaborates on the new "triple threat study" published in Nature which seems to validate, along with NASA's study, James Hansen's concerns. About 40% of the US population lives in coastal cities – where flooding in the wake of storms is already proving increasingly costly in built-up areas, swamping subway lines and electricity stations.But the Nature study was among the first to explore the combined risks under climate change of sea-level rise, heavy rainfall and storm surges over broad stretches of the US
In the case of New York City, the risks of flooding – because of that combination of factors – has doubled over the past 60 years, the researchers found. A 4ft storm surge, combined with 5in of rainfall, could be heading New York City’s way once every 42 years, compared to about once in a century in the 1940s.
The increased risk was due to the combination of storm surge, rainfall and flooding.
“They are all somehow interconnected,” said Thomas Wahl, the University of South Florida researcher who led the study. “If sea levels continued to rise, this would certainly have an effect on storm surges, and storm surges have an effect on compound flooding.”
What that means is that it would not necessarily take a huge amount of rainfall to put New York or other cities underwater – a storm surge could do that on its own, Wahl said.
From the abstract: When storm surge and heavy precipitation co-occur, the potential for flooding in low-lying coastal areas is often much greater than from either in isolation. Knowing the probability of these compound events and understanding the processes driving them is essential to mitigate the associated high-impact risks1, 2. Here we determine the likelihood of joint occurrence of these two phenomena for the contiguous United States (US) and show that the risk of compound flooding is higher for the Atlantic/Gulf coast relative to the Pacific coast. We also provide evidence that the number of compound events has increased significantly over the past century at many of the major coastal cities. Long-term sea-level rise is the main driver for accelerated flooding along the US coastline3, 4; however, under otherwise stationary conditions (no trends in individual records), changes in the joint distributions of storm surge and precipitation associated with climate variability and change also augment flood potential. For New York City (NYC)—as an example—the observed increase in compound events is attributed to a shift towards storm surge weather patterns that also favour high precipitation. Our results demonstrate the importance of assessing compound flooding in a non-stationary framework and its linkages to weather and climate. We are out of time. Will we as a species be able to address this issue with the urgency that is needed?