Climate scientist Cynthia Rosenzweig has been studying the impacts of global warming on New York City since the 1990s, and was part of a group that analyzed the unique risks faced by the Big Apple way back in 2001. The group's report predicted what a once-a-century superstorm like Hurricane Sandy proved: the Brooklyn Battery Tunnel between major boroughs flooded, La Guardia Airport runways were underwater, and so on.
More recently Rosenzweig helped chair the New York City Panel on Climate Change, brought together to update the city on the latest climate science and to help city agencies prepare to adapt. The Mayor's Office calls such preparation "climate resilience"—and it got a trial during and after Hurricane Sandy as well as Hurricane Irene in 2011.
Scientific American spoke with Rosenzweig, head of the climate impacts group at the NASA Goddard Institute for Space Studies, while she prepared her Tarrytown home—threatened by trees listing in the wake of Sandy—for yet another northeaster storm.
[An edited transcript of the interview follows.]
Did you predict Superstorm Sandy's impacts, in some sense?
Sea-level rise and climate change were already on the radar screen in the New York metropolitan region way back in our  report. In that report we have the critical elevations, the one-in-500-year projections for the [flooding] impact on the Brooklyn Battery Tunnel and all the La Guardia [airport] runways.
What could or should have been done differently to better prepare the metropolitan region for such a huge storm?
Virtually everything that happened [after Sandy] had been highlighted in our reports. What we're doing now is going over the science of Hurricane Sandy and identifying the scientific work that needs to be done. One [task] is this key issue of redefining the one-in-100-year storm. Everyone is saying: "What's up with this one-in-100-year storm happening every year?" But scientifically we still need to look at the data and address if there should be a change. Our reports have noted that the one-in-100-year storm is now one in 15 to 35 years, on the conservative end [not assuming rapid meltdown of glacial ice in Greenland and Antarctica].
Mayor Bloomberg had initiated a climate change adaptation task force with 40 agencies. New York City is one of the leaders in this country and even the world in setting up adaptation and assessing how climate risks are increasing. All of this had begun, but to have an event of this very large effect and impact—a one-in-a-multi-century storm—would be challenging for any city in its path. It's just that this was such a whammy. That's the nature of risk.
The [Metropolitan Transit Authority] had clearly learned how to shut down the subways [after Hurricane Irene in 2011]. It's not a complete surprise. It's almost a: "Yes, we've been learning about this, understanding that the risks are increasing and, in fact, now for sure they are."
Any loss of life is unacceptable [but] the loss of life and the damage would have been so much greater, think of it, if we hadn't had the evacuation plan in place and also closed the subways and the tunnels. It could have been far more devastating.
Do we need to retrench, pull back from the coasts because of sea-level rise or rebuild differently? Where do we go from here?
We need an integrated approach that covers three areas: engineering, ecologically based adaptation and policies. Let's take engineering. There is a whole spectrum of engineering approaches, like innovative designs for subway grates. Right now we have open grates. We need to design and implement grates that close. We need to see what we can do with the tunnels, which is much more challenging. We need to think about drains. Some of those are innovative engineering solutions, some involve standards and regulations, like building culverts to withstand more drainage.
At the other end of the engineering spectrum is tidal barriers. What we recommended on that issue is: it needs to be studied. We need to begin the next set of feasibility studies: a significant study of the costs, benefits, feasibility in our New York coastal estuary, and the economic, environmental and societal costs and benefits. There is a lot of cost involved in creating such a big, engineered structure. There would be environmental changes we would need to understand. On the societal side: Which areas are protected? Some would be, some would not be, and how do we deal with the communities in different places?
The second part is ecologically based adaptation. There are the wetlands [that can absorb] coastal flooding, but there is also inland flooding. We also coexist with a wonderful, mixed deciduous and evergreen forest here. How can we coexist with a forest ecosystem in more effective ways, because of the damage caused by trees falling into power lines or trees falling into houses? Then again, having forested areas is good in terms of absorbing storm water. How can we really develop ecosystem-based adaptations that are effective for our region?
The third area is design and policy. Right now, what we call the societally acceptable level of risk is basically the one-in-100-year storm. Sandy was a wake-up shout for us all to think about: Is that the right level or do we need to change that? Is it really now the one-in-500-year storm? Or, as in Europe, is it even more?
Then there's coastal communities. Can there be a reduction in insurance premiums for homeowners who take adaptive measures? That's an incentive for doing a better job.
Overarching all of this is design, urban planning. What we really need to do is recover, rebuild and create a vibrant and sustainable coastal city region.
Let's do this in creative ways. For example, the Dutch are not just looking to engineering solutions, they are looking at a mix of solutions. So there are the iconic floating houses but they are also doing a lot with raising apartment buildings and allowing water to slosh in and out when floods come. We have to accept that we are a coastal region. There are going to be coastal floods. How do we live with it?
Is there enough room in New York City for things like wetlands to make a significant impact?
We have about 1,500 miles [2,400 kilometers] of coastline in the estuary. One of the things we need to do is see what areas are available to restore or maintain or reconstitute. The [New York City Department of Environmental Protection] has already started that with the Bluebelt Program [preserving wetlands for storm water management in Staten Island]. How did those work during Sandy? It was a very large storm. Did they work for a certain amount of time or up to what level of flooding? What's the potential for expanding those areas?
It's the same with porous pavements. They are installed in 300 relatively small areas. What scale do we have to do with those interventions to have them be effective? That's a research question.
What is a city's role in combating climate change, given its global scale?
Cities are emerging as the first responders. It's of necessity. It's the right level of governance to deal with these superstorms and enhanced coastal flooding due to sea-level rise. They see their constituents every day, they don't just helicopter in and helicopter out.
One of the neglected aspects of Superstorm Sandy is the challenge to people as well as infrastructure. How do we improve the climate resilience of people?
There's a tremendous strain on everyone, and you can see the vulnerability. I spent the storm with my 97-year-old mom. We've raised those issues but we need to do much more. There's also the health aspect. Like in New Orleans, there's mold [after flooding].
We need to work on this social aspect. I was on a conference call yesterday with a colleague from Bangladesh. He offered to send help because they have a lot of experience dealing with this, especially the social aspects. They've created in Bangladesh an explicit social network around flooding. People know: this is the group of people I'm going to be caring for. People who [live at low elevation] are connected to people who are high. That leads into this mental health aspect. If people feel part of all that, it will help. That's why the volunteering has just been fantastic. New Yorkers are fantastic in terms of their community response. Let's study that more. How can we nurture and strengthen those community mechanisms?
Do you think Sandy will change the conversation about climate change?
Is this a tipping point? I think it is, in terms of response. I don't think in six months people are going to say "Hurricane Sandy, what was that?" Certainly not in the New York metropolitan region. Everybody now knows that storms are different. This one-in-a-multi-century storm [in terms of risk of occurrence] is a wake-up shout.