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Climate Effects on NYC May Move Faster Than Previously Forecast

NYC 100yr flood zones NYUThe impact of climate change on New York City could be even more severe than previously thought, putting more people at risk from increasingly frequent floods and heat waves, according to a report by the New York City Panel on Climate Change that was released Monday.

New maps projecting the impacts of a 100-year storm show that by 2050, nearly a quarter of the city – 72 square miles – could be flooded, potentially affecting 114,000 buildings, 97 percent of the city’s power generating capacity and some 800,000 residents, according to a separate city analysis.

The climate panel’s first report, issued in 2009, warned that climate change would cause increased heat waves, higher storm surges and more frequent and intense downpours within a few years. While largely consistent with that analysis, Monday’s updated projections suggested that some of the more extreme climate impacts could happen sooner than previously anticipated. Sea level in particular is now predicted to rise faster than previously thought.

Hurricane Sandy, MTA, subway
A subway station flooded by Sandy. Photo: MTA

“The overall numbers are similar, but we have more compelling evidence now that (a more severe scenario from 2009) is looking like a more realistic possibility now,” due to improved computer models and more evidence that some ice sheets are melting, Radley Horton, a climate scientist with the Earth Institute and a researcher with the city climate panel, told the Associated Press.

The panel, which was convened by Mayor Bloomberg in 2008, was reconvened in 2013 in the wake of Hurricane Sandy to provide updated projections and to develop new coastal flood risk maps to inform the mayor’s post-Sandy rebuilding initiative. Co-chaired by the Earth Institute’s Cynthia Rosenzweig and William Solecki, the director of the CUNY Institute for Sustainable Cities, the panel consists of over a dozen leading climate and social scientists from the top research universities in the region, including the Earth Institute, Lamont-Doherty Earth Observatory and others from Columbia University.

According to the new report, by the mid-2020s, annual temperatures in New York City will rise by 2 to 3 degrees on average, even as the number of summer heat waves to increases from two, to three or four per year.

By the 2050s, the panel projects that temperatures in New York City will rise by 4 to 6.5 degrees, perhaps doubling the number of days over 90 degrees. Sea levels at the Battery in southern Manhattan–which have already risen by 1.1 feet since 1900–will rise 11 to 24 inches, with 31 inches at the high end of projections.

This contrasts with the 2009 report, which predicted a mid-range rise of 7 to 12 inches by 2050. Sea level rise greatly increases the risk and intensity of coastal flooding. The intensity and extent of heavy downpours is also very likely to increase, the panel reported.

Bloomberg on JoeOn Tuesday, Mayor Bloomberg followed up on the panel’s report by outlining a $20 billion plan that includes 250 recommendations to protect at-risk neighborhoods and critical infrastructure from projected climate hazards. The plan’s recommendations include the building of bulkheads and levees and the creation of tidal barriers and wetlands. It also includes plans to address risks to energy, transportation, telecommunications, wastewater and healthcare services, among other sectors.

The mayor described the initiative as a “tailored, multi-layered approach that prioritizes the areas most at risk, with the most vulnerable populations and most vulnerable infrastructures…Make no mistake: this is the defining challenge for our future and if anyone is up to the task of defending the city they love, it’s New Yorkers.”

While the wide-reaching impact of Hurricane Sandy has sparked an unprecedented new public interest in climate change, the panel is quick to point out that it is not possible to attribute any one event to climate shifts. However, there is little question that climate change-related sea level rise did increase the impact of coastal flooding from the storm. Because of sea level rise alone, the panel estimates that by 2050, 100 year flood events may happen five times more frequently than they do now, if the highest estimates for sea level rise are realized.

And while scientists do not currently know if climate change will increase the total number of hurricanes globally, the report concludes that it is more likely than not that the number of very intense hurricanes will increase in the North Atlantic Basin.

Other potential impacts include the increased risk of heat stress and heat-related mortality. Heat indices, the report says, are very likely to increase, both because of rising temperatures and because warmer air can hold more moisture. This combination of high temperature and high humidity can easily create heat stress by shutting down the body’s ability to cool itself. More hot days also puts extra stress on the region’s aging power grid, increasing the likelihood of blackouts.

Cynthia Rosenzweig
Cynthia Rosenzweig

“The inclusion of increasing risks due to climate change in the post Hurricane Sandy rebuilding of New York City is a positive tipping point for climate policy and action – not just for New York City, but for cities around the world,” said Rosenzweig and Solecki, of the City’s Panel on Climate Change. Rosenzweig works at the NASA-Goddard Institute for Space Studies, an affiliate of the Earth Institute.

Also serving on the climate change panel from the Columbia are Vivien Gornitz of the Goddard Institute and the Center for Climate Systems Research; Klaus Jacob and Yochanan Kushnir of the Lamont-Doherty Earth Observatory; and Patrick Kinney of the Mailman School of Public Health.

“One of the goals of Columbia University’s Earth Institute has been to ensure that sustainability policy is based on the best possible scientific knowledge,” said Steven Cohen, executive director of the Earth Institute. “A number of Columbia University Earth Institute scientists were deeply involved in this effort, and we pledge our continued support to help New York City in any way we can to meet the challenges identified by this state-of-the-art plan.”

(This post was updated on June 24, 2013, to include the flood zone map.)

Banner featuring a collage of extreme heat images.

Recent record-breaking heat waves have affected communities across the world. The Extreme Heat Workshop will bring together researchers and practitioners to advance the state of knowledge, identify community needs, and develop a framework for evaluating risks with a focus on climate justice. Register by June 15

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