Planning for a Climate-Changed World
As the global picture grows grimmer, states and cities are searching for the fine-scale predictions they need to prepare for emergencies--and to keep the faucets running.
By David Talbot
On December 11, 1992, a powerful northeaster coalesced off the eastern seaboard of the United States, and an eight-foot storm surge struck New York City. Seawater swamped the Brooklyn Battery Tunnel to a depth of six feet, cascaded down PATH subway stairs in Hoboken, NJ, and forced LaGuardia Airport and many roads and subways lines to close. Had the storm been slightly stronger, a 10-foot surge could have devastated a far wider region, inundating low-lying areas like Coney Island and Manhattan's financial district and overwhelming the 14 sewage plants dotting the New York City coastline.
A flood of comparable height in New York City's environs should occur about once every 100 years, on average, in the estimation of one Columbia University study. But global warming and rising sea levels--as well as the possibility of more-intense precipitation, stronger storms, and altered storm trajectories--will make such disasters more frequent. And to protect the people who live and work where disaster threatens, the critical first step is to determine how quickly and by how much, exactly, the threat is increasing. That knowledge is essential to deciding how seriously to consider specific countermeasures; for New York, these could range from mandatory evacuation plans for seaside neighborhoods to multibillion-dollar storm-surge barriers spanning the Verrazano Narrows and other key channels.
But there are no clear answers, and part of the problem is that well-documented predictions about planetary change haven't generally been broken down in local terms. Though the Intergovernmental Panel on Climate Change (IPCC) has concluded with 90 percent certainty that human activity is warming the planet--and spelled out the likelihood of consequences that include higher seas, droughts, and fiercer storms--the United States is committing scant resources to providing usable information to the people who respond to emergencies, plan for urban development, manage coastal areas, and make sure the crops keep growing and the reservoirs stay full. "The challenge is to increase our capability to accurately forecast climate at the regional level," says Ronald Prinn, an atmospheric scientist who directs the Center for Global Change Science at MIT. "That is what is needed in order to improve the information that government agencies get--[and] to then translate those regional forecasts into something useful at the city [or] state level." Equipping people to deal with climate change could mean simply giving state and local planners access to a wealth of existing information--such as calculations made by the National Oceanic and Atmospheric Administration (NOAA) that could indicate how far inland storm surges would move if sea levels were higher. But it will also mean sharpening local and regional models, so that they can predict the effects of climate change in far greater geographic detail. And it will require new approaches to emergency planning, water-supply management, and more.
Global warming will affect different regions in different ways. In 2000, a national assessment by the U.S. Global Change Research Program (USGCRP) warned generally about potential climatic changes in what it called "mega-regions" of the nation. "What we were able to do at that point was very limited," recalls Michael MacCracken, an atmospheric physicist, now retired, who coördinated the assessment effort. And the study's climate scenarios were based only on global models: "We really wanted to have more models, and more regional results, but we had very little resources to get that done." Similar, very general statements about climate change across large regions appeared in the most recent IPCC assessment, the first time the IPCC has narrowed its focus even that much. The report pointed out, for example, that the southwestern United States will probably get even more parched than it is now. But what we need are projections on a far finer scale. With federal climate-science budgets cut to the bone in recent years, a few state and local governments are funding their own efforts in New York, California, and western states eyeing dwindling water supplies with alarm.
A Wet New York City
Rushing into her office near Columbia University, Cynthia Rosenzweig was chipper despite her evident exhaustion. An agronomist by training, she directs the Climate Impacts Group at NASA's Goddard Institute for Space Studies (GISS) and advises New York City's government on how climate change will intensify heat waves, stress upstate watersheds, and increase the risk of a devastating storm surge. She had just returned from Delhi, India, where she cowrote a summary of the 2007 IPCC reports, the first of which was released in February. Brightly painted papier-mâché elephants she'd brought back from her trip were arranged on the coffee table in her sixth-floor office overlooking 112th Street (as it happens, some of the highest ground in Manhattan). She sat down and, on her computer screen, called up images from a GISS global climate model.
Honed by a broad range of climate scientists, the model represents atmospheric and oceanic systems. Like other global models, it simulates interrelated processes: for example, the warming of Earth's surface by solar radiation; the absorption of heat by the oceans; the reflection of solar energy by land surfaces, ice sheets, and particulates in the atmosphere; and the effects of the accumulation of excess carbon dioxide and other atmospheric gases that trap heat. Researchers test the accuracy of such models by seeding them with, for example, data on actual greenhouse-gas emissions over the past 30 years and then seeing whether they return results consistent with temperature and other measurements recorded over that period. The goal, of course, is a model that can predict how much temperatures will continue to rise given various future greenhouse-gas emission levels, and how other parts of the climate system are likely to respond.
But the limitations of global models quickly become clear when Rosenzweig zooms in on a map of the eastern United States showing climate predictions for the 2050s. On the screen, a line cuts from eastern Pennsylvania to western Massachusetts. The area north of the line is yellow, representing a 2 ºC increase over historical averages; the area south of the line is more orange, indicating a 2.25 ºC increase. The entire New York metropolitan area, Connecticut, and much of Massachusetts and New Jersey are lumped together under a single temperature estimate. The same goes for several other variables, such as precipitation and evaporation rate. The problem is that one "grid box" in the typical global climate model--think of it as a pixel in a photograph--is a square of 150 to 200 kilometers per side.
Weather and climate are, obviously, far more localized than that. Mountain ranges--even individual peaks and valleys--make their own weather. A single glacier might grow or dissolve because of temperature and rainfall changes in a very specific area. Differences in air temperature over water and land cause breezes that can dramatically influence climate and weather in coastal areas. Regional models that take such phenomena into account are familiar to any viewer of TV weather news. But where global models are calibrated against data spanning decades, regional models are used to project only a few days ahead. Thus, one goal of climate scientists is to find a way for the twain to meet, to give local precision to predictions about global warming and climate change.
Rosenzweig's group has calculated that today's one-in-100-years New York flood would, in the 2080s, be considered a one-in-40-years or perhaps a one-in-four-years event. The order-of-magnitude difference is simply the result of variations between models. To calculate a more useful range of probabilities, Rosenzweig is currently combining global models with regional ones. By "nesting" models of smaller regional areas in the global grid boxes, she hopes to increase the resolution of climate-change predictions to 10 to 15 kilometers. In six-hour time increments, a global model introduces a fresh batch of climate variables into the regional models, which then make local calculations.
The project is ongoing; so far, efforts to validate such nested regional models against actual temperature measurements have shown the predictions to be off by 1 ºC or more, an unacceptable margin of error. Still, Rosenzweig expects that regional models will become more precise with further work. And as they do, one of their uses will be to better predict storm surges by accounting for changes in local wind patterns. "The large majority of climate impact studies have been done with the GCMs," Rosenzweig says, referring to global climate models. "We are just now beginning to do more with the RCMs [regional climate models], and they are very much in research mode. Sea-level rise is the number one vulnerability, and we need better information for the agencies. It's critical for their planning."
To be sure, global sea-level projections are still a matter of debate: the IPCC pegged the 21st-century increase at between 18 and 38 centimeters under a scenario that assumed lower greenhouse-gas emissions and between 26 and 59 centimeters with higher emissions. This uncertainty makes perfect storm-surge predictions impossible. But the lack of information about local climate change remains a stumbling block that prevents New York City--and every other coastal area--from developing the detailed information it can act on. "You don't always protect against the worst case, because you would bankrupt the city," says Rohit Aggarwala, director of long-term planning and sustainability under New York's mayor, Michael Bloomberg. "How urgent is it to invest in multibillion-dollar projects? Knowing that over the whole Atlantic seaboard there will be x sea-level change and x change in violent storms doesn't necessarily help New York City make different decisions than Miami or Halifax." On the other hand, he notes, if New York were to operate on incorrectly optimistic information and delay the most ambitious storm-surge barriers too long, the consequences could be disastrous.
New York City authorities have already gotten some specific warnings from Rosenzweig's group, which made a study of how the city's water-supply and sewage-treatment infrastructure could be affected by rising sea levels. For example, a pump station north of the city on the Hudson River--built to draw emergency fresh water during times of drought--will eventually require expensive new filtration systems as rising seas push salinated water to within range of the intake areas.
But while there's still uncertainty about the rate at which sea levels are rising, it has become increasingly clear that temperature increases alone could severely tax a large city's infrastructure. Late last year, the Union of Concerned Scientists in Cambridge, MA, released a report titled "Climate Change in the U.S. Northeast." Produced in collaboration with climate scientists, the report predicts that by midcentury, northeastern cities could be experiencing an average of 30 to 60 days of temperatures above 90 ºF each year, up from 10 to 15 days historically. By the end of the century, these cities could see 14 to 28 days of temperatures over 100 ºF, if the higher-emission scenarios are realized.
Armed with such predictions, the city of New York and a prominent regional civic-planning group, the Regional Plan Association (RPA), are starting to think about how to respond. Jennifer Cox, a senior planner and director of geographical information systems at the RPA, is superimposing estimates of heat waves and storm surges onto city maps showing topography and socioeconomic characteristics. And GISS is collaborating with a consortium of universities whose members are now plugging temperature estimates into air-quality models, to see how bad ozone levels could get during the hotter summer days of the 2040s or 2060s. High ozone levels could produce severe health crises as heat waves overwhelm emergency facilities, water supplies, and the power grid.
But such studies are just the first academic pass at planning. The scenarios they envision are still relatively vague. And while suggested remedies abound, they reflect more imagination than engineering. Physical oceanographer Malcolm Bowman of the State University of New York at Stony Brook, for one, would place a tidal-surge barrier at the Verrazano Narrows (between Brooklyn and Staten Island); another near the Throgs Neck Bridge, where the East River meets Long Island Sound; another between Perth Amboy, NJ, and Staten Island; and a fourth across Rockaway Inlet at the entrance to Jamaica Bay. The barriers--more ambitious versions of the storm-surge barrier at the mouth of the Thames River outside London--could theoretically prevent tens of billions of dollars in damage. With the models and computational power available now, however, it's hard to determine whether and when such ideas need to be acted on. "If you look at European experience," says Bowman, "it takes a major flood and a major loss of life to get the bureaucracy to do anything."
Other sections of story--
- The Dry West
- The Canaries
- Staggering Backwards
- Vanishing Yosemite Snowpack
David Talbot is Technology Review's chief correspondent.
Link to online story. Archived here.
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