Reflecting the uncertainty that plagues most analyses of potential impacts of climate change, Rosenzweig and her colleagues decided to devise two separate projections for future sea level rise: a standard projection and a so-called "Rapid Ice Melt Scenario" projection. Their standard projection concludes that New York must prepare for 7 to 12 inches of sea-level rise by 2050 and 12 to 23 inches by 2080—a considerable but manageable amount. But if, as James Hansen and some other leading climate scientists feared, the earth's polar ice melts at a rapid rate in the years ahead, the Rapid Ice Melt scenario will tell New York infrastructure managers that they could experience 19 to 29 inches of sea-level rise by 2050 and 41 to 55 inches by 2080—a much more challenging scenario.
Officials cannot make prudent decisions without also improving their knowledge about New York's existing risks, said Adam Freed, the city government's deputy director of long-term planning and sustainability. "We need much better flood maps," Freed told me in April 2010. "Our current maps have a margin of error of three feet. So when Rosenzweig's group projects two feet of sea-level rise by 2080, or by 2050 under the Rapid Ice Melt Scenario, our current maps could be massively underestimating the total land area that could flood. Or they could be massively overestimating it. We just don't know."
To rectify the problem, the city has begun deploying an aerial technology known as LIDAR (Light Detection and Ranging). Airplanes are flown over the city's landmass and a special laser pulse is sent to earth that measures a given area's elevation much more precisely than the technologies that inform flood maps compiled by the United States government's Federal Emergency Management Agency (FEMA).
Nevertheless, mitigation remained the Bloomberg administration's top climate priority, and its officials made no apologies for that. "I'll be honest: I fully support adaptation, but I want it to have a lower profile in order to keep the pressure on for aggressive mitigation," said Rohit Aggarwala, the director of the city's Office of Long-Term Planning and Sustainability and the mayor's point person on PlaNYC.
But mitigation has proven a difficult struggle for New York City. One reason is the state government, which in 2008 voted down Bloomberg's proposal for congestion pricing after the New York City Council had approved it. That defeat in turn undermined Bloomberg's proposed expansion of mass transit, which was to be financed in part by congestion fees. The state government had also declined the city's request for a sixfold increase in energy efficiency funding. "Changing the carbon footprint of a city as big as New York is like changing the direction of a supertanker," Aggarwala told me.
He seemed more optimistic the last time I interviewed him, in April 2010. New York's electricity consumption per capita had finally fallen in 2008, the most recent data that was available. On the adaptation side of the challenge, a new power plant being built in Sunset Park was being elevated four feet above its original design level to cope with sea level rise. The Parks Department was planting only trees that could manage the heat and precipitation conditions anticipated in the future.
Aggarwala did confess to one lingering frustration. "We have to get people to understand the difference between prevention and resilience," he said. "Some people think we can keep climate change out somehow; you just build a seawall or a dome or something. You can't do it. Subways, for example, you can never perfectly protect. They are below sea level by definition and you can't seal them because you need the heat down there to get out. Instead, our goal has to be to increase our resilience, to get our people and infrastructure through whatever impacts occur as smoothly as possible. But lots of people just want a quick and easy fix. It's the same mentality as buying a Hummer that runs on bio-diesel—the idea that if I just change this one thing, I can fix the problem. It's delusional. And insanely frustrating."
But he was also encouraged that "the level of understanding of the likely impacts of climate change among the people who manage the city's critical infrastructure, both public and private, has increased tremendously, and that alone has reduced our risk," he said. "Those people are making much better decisions now."
This piece was produced by the Climate Desk collaboration.