Adapting to Climate Change:Rising Sea Levels, Limiting Risks
Climate change and resulting sea level rise will cause risk from coastal storms to increase throughout this century. Aggressive implementation of emissions reduction policies would significantly limit the risk but in any event, planning for comprehensive adaptation is necessary. Past experience with long term planning to reduce vulnerability and exposure along the coast shows a significant shortfall between the need to reduce risk and the implementation of appropriate policies. A new approach to public policy in this arena should be a priority for policy makers.
among the messages communicated at the social research conference on climate change is this: fear of disaster is a poor motivator to action because fear is paralyzing. Rather than just dole out frightening scenarios, people interested in generating proactive responses should give potential victims a way out of a bad situation. In that context, the picture I am going to present may be discouraging to some. But climate change is a problem that can be solved through a combination of reducing emissions that cause climate change and the associated sea-level rise as well as increasing the capacity to adapt to the changes that are inevitable. In this article, I focus on the latter necessity—the potential for adaptation—as well as lessons from the past on the difficulty of actually meeting such a challenge. We live in a society where thinking over the long term is not necessarily what government officials and other leaders are accustomed to, even those whose job it is to do so. In politics, it is easier to act with a short-term view or even act in a way that is counterproductive to long-term objectives.
Solving a problem like climate change requires a different way of thinking because, unlike the earthquake risk Guy Nordenson discusses in his paper elsewhere in this issue, climate change is a dynamic problem. Climate is going to change continuously in somewhat unpredictable ways, sea levels will be rising, and storm intensities will be altered as well. Our track record on managing garden-variety [End Page 673]
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climate risks in what seemed to be a stationary climate is not especially encouraging. Hence I question our ability to successfully manage a situation where risk needs to be continually reassessed.
How does climate change affect New York City? The earth has exhibited a warming trend over most of the past 150 years, as shown in figure 1. The past decade has been warmer than any other previous one. Overall, the earth has warmed over 0.8°C (about 1.5°F) since the late nineteenth century. That increase is very significant in the his-torical context, and is the beginning of a much larger warming that is inevitable unless emissions of carbon dioxide and other greenhouse gases are brought under control. Combustion of fossil fuels, which largely power our society, is the major source of these gases. Accordingly, the socioeconomics of fossil fuels makes reduction of our dependence on them a difficult task, one that can only be accomplished over many decades.
I will focus here primarily on one critical consequence of global warming: rising sea levels. As figure 2 indicates, sea level has risen about 15–20 centimeters (about 7 inches) over the past century. Generically, there are three causes of this trend: the ocean, like any heated fluid, expands as the world warms; mountain glaciers are also warming and melting, adding additional water to the ocean; and likewise, the major ice sheets on Greenland and Antarctica are disintegrating gradually, especially at their warmer peripheries. Figure 2 also shows that the rate of rise has increased. The recent rate of rise is about 3 millimeters per year, much faster than in preindustrial times. The total rise of seven inches may not sound like a lot, but if sea level rises by a foot vertically, it takes away, through submergence and erosion, about 100 feet of coast in the inland direction on a typical US East Coast beach, such as already occurs where land is not protected or restored. Even some preventative actions, such as building jetties, protect one stretch of beach while taking away sand from somewhere else.
Figure 3 shows future projections of temperature change. The map illustrates two vastly different worlds. The lefthand panel shows a future where fossil fuel emissions have been gradually eliminated [End Page 675] over this century. The world is warming, but at a manageable rate, and it is headed toward a stable climate. In this future, changes in precipitation are relatively modest. Sea levels would rise about another 30–60 centimeters (1–2 feet), which would be challenging but perhaps manageable, at least for rich countries. But even in this projection, conditions will become difficult for some, particularly those living in poorer parts of the world, or for poor people living in the richer parts of the world. With planning and luck, most of humanity would probably thrive, although other species, with a lower capacity to adjust, will experience greater difficulty.
The righthand panel, however, shows the whole world turning extraordinarily warm; this will be accompanied by large areas of drying. This state of the world is one that I and most of my colleagues believe would be disastrous even for the wealthy countries, where the warming would be so quick and the sea-level rise would be so rapid, that individuals and societies would not have the ability to adjust successfully.
How can we frame the question of how to manage the risks associated with these changes? Risk arises from a combination of these physical hazards with vulnerability and exposure of people, infrastructure, and ecosystems. Vulnerability and exposure interact to [End Page 676] enhance risk (potential damages and harms). Thus there are three ways to deal with the risk: (1) reducing the physical aspect or hazard, the climate change itself, by cutting emissions; (2) reducing vulnerability, defined as lack of resilience or of the ability or resources to defend oneself, by improving the human and societal capacity to respond; and (3) reducing exposure—being in the wrong place at the wrong time, like living close to the sea in an area which experiences hurricanes—by sensible land-use policies, especially at the local level.
For example, as sea level rises, coastal storms will push the higher sea to levels and into inland places where it has rarely, or never in human memory, gone before, creating record high flood levels, more and more frequently, all along the coast. One way to imagine this is to consider the 5-foot sea wall around lower Manhattan. Currently, this wall is overtopped in storms occurring once every 10 years or so. Due to its particular geophysical location, New York is subject to higher sea-level rise than the global average. As a result, by midcentury, sea-level rise combined with such coastal storms could cause it to be overtopped more often than once per year, causing considerable flooding.
Flooding from Hurricane Sandy reached levels at the Battery that historically occur roughly once in 1,000 years. By the end of this century, such flood levels could occur every 20 years and still more frequently thereafter even if the intensity of storms do not change, simply due to sea level rise. It takes a long time to recover from such an event, especially considering that smaller but still painful ones will be happening in between the big punches.
Figure 4 shows the 10 highest coastal flood levels experienced in the past 65 years in New York City. It also demonstrates why even a modest sea level rise of 1–2 feet can radically alter the impact of such events. The dashed line marks high water of 10.5 feet, the point at which the NYC subway system floods. With the exception of Sandy, which was the first to flood the system, all the other storms came within about a foot or two of doing so. Only 1 or 2 feet of sea-level rise make the difference between a flooded subway system and a more or [End Page 677] less dry one. We were very lucky with Sandy. Through diligent efforts by the Metropolitan Transit Authority staff, and some luck, the flooding did not take down the system for more than a few days. But we came very close to losing the subway for months.
The city and the state are not standing still in the face of climate risks. A comprehensive plan from the Special Initiative on Rebuilding and Resiliency (SIRR) proposed exploring natural defenses of the sort that Guy Nordenson points to for Jamaica Bay, along with modest sized “gray” (e.g., concrete) defenses and artificial reefs, and also some bigger projects, including storm barriers, and a large, permanent project in the South Street Seaport area, involving an immense real estate development. The question is, how much of this will ever get done? Some of it, the no-brainers like moving hospital emergency generators and fuel out of basements, is happening. But what about the projects that require planning, foresight, and considerable revenue? [End Page 678]
In a word, the risk is increasing. Harms we know could happen but currently consider unlikely will become more likely in the future. I am sure the people who placed emergency generator systems in basements knew that if a flood was high enough, the generator could go out, but they counted this as very unlikely to occur, perhaps less often than once in 100 years. If you construct a building now, it has to be ready to endure that level of flooding once every 20 years, 10 years, or even every 5 years, and so on as we move toward midcentury, still within the lifetime of the infrastructure.
This is not easily fixed, not so much due to technological obstacles as to the political difficulties. For example, the SIRR plan talks about protecting subway tunnels and suggests raising or redeveloping the subway vent system so water does not simply pour into the subways, but that is subject to available funding, and if you add up the costs, they are significant. City leaders need to give this threat the attention and priority they gave the third water tunnel—a project which has taken many, many decades to complete and has been delayed by financial crisis but is now nearing completion.
The De Blasio administration has not given building such resilience the same level of priority as did the previous administration (on which time ran out before much could be done in the wake of Sandy). I hope the current administration refocuses with full force on the climate risk. You cannot solve this problem by putting it off indefinitely. The mayor gives a higher priority to the housing crisis, also a crying need. But it will not do much good to densify this city while it is being eaten away around the edges for lack of attention to sea-level rise.
Let me provide an example of what happens when resilience building is deferred, an example of policymakers not learning. The 1992 nor’easter flooded the PATH station in Hoboken and nearly flooded the NYC subways. That was a lesson quickly unlearned and forgotten, making the flooding of the subway in Sandy inevitable. At one point, people who planned the infrastructure knew this could happen, and they started to plan against this actuality, but then, in a few years, gave up the effort. Other priorities intervened because there are serious [End Page 679] obstacles to timely action, to staying focused, including the fact that episodes are infrequent, memories are short, planning times are long, risk increases continuously, and political incentives are perverse compared to the requirements of risk management.
Finally, even if we do not get the big things done, we can at least do the simple things, many of which are quite effective. Bangladesh is a poor country where too many people live in a small space and are very vulnerable to sea-level rise. Many people have died when cyclones have struck the southern coast along the Bay of Bengal, as many as 1 million people in a 1970 storm. Eventually the government installed early warning systems and concrete emergency shelters and now the death rates, while still appalling, are down in the thousands. We, here in New York City, need to start with low-regret strategies on an everyday basis while we think about the bigger things that may eventually need to be done.
michael oppenheimer is the Albert G. Milbank Professor of Geosciences and International Affairs at Princeton University and Director of Princeton’s Program in Science, Technology and Environmental Policy (STEP). His research focuses on the science and policy aspects of climate change and its impacts.