Hot Nights in the City: Global Warming, Sea-Level Rise and the New York Metropolitan Region
By Janine Bloomfield, Ph.D., Staff Scientist
with Molly Smith and Nicholas Thompson
June 1999
Executive Summary
New York City has close to 600 miles of coastline. Four out of the five New York City boroughs are situated on islands, linked together and to the mainland by about 80 of the approximately 2200 bridges and tunnels in the City. Entry points to many of the tunnels and much of New York City's subway system lie less than or near to ten feet above sea level as do the three major airports serving the New York City Metropolitan Region. New York City may be the capital of the world, but it is also vulnerable to global warming and resulting increases in sea level.
A range of climate-change scenarios was examined in this report. By the year 2100, New York City is expected to have as many 90-degree-plus days as Miami has today in the best case (double New York's current levels) or almost as much as Houston in the worst-case scenario (more than six times New York's current levels). But the threats from global warming extend well beyond the heat. Sea-level rise will contribute to the temporary flooding or permanent inundation of many of New York City's and the region's coastal areas as increased sea levels accentuate the impact of the storms that already strike the region. Erosion could devastate valuable beaches and wetlands and, as has happened in the past, we can expect that homes will be swept into the ocean by storms. In 1992, a powerful nor'easter shut down New York City's subways, trains, highways and airports, battered coastal residences and caused substantial beach erosion. By the 2050s, storms with flooding of the same magnitude as the '92 nor'easter are projected to occur from once every 18 to once every 8 years, depending on the scenario. By the year 2100, the range drops to from once every 13 years to about once per year.
Global warming is projected to lead to wider swings in rain and snowfall along with warmer temperatures year-round and possible increases in both droughts and flooding from downpours. Higher temperatures alone contribute to the increase in frequency of droughts. In some scenarios, the risk of drought is magnified as precipitation decreases as well. Droughts can affect water supply, such as during the drought of the 1960s, when New Yorkers had to drink water from the Hudson River mixed with water from the normal sources. Some scenarios project much wetter conditions that could mitigate droughts. However, the same conditions would increase the risk of inland flooding. Increased temperatures could also lead to more heat-related mortality, enhanced levels of ground-level ozone that cause acute respiratory distress and chronic damage to the lungs, and an increased chance of the re-introduction into New York of mosquito-borne infectious diseases such as malaria.
There is a scientific consensus that emissions from the burning of fossil fuels, deforestation, and agriculture, have caused an accumulation of greenhouse gases in our atmosphere which is already altering Earth's climate and is expected to have a much more powerful impact in the future. This report is based on computer simulations of future climate that have considerable uncertainty when applied to a small region. Nevertheless, the trends in these simulations are indicative of the risks for the New York Metropolitan Region. Global climate models used in this study project that, by the year 2030, average temperatures in New York City could increase by about one to four degrees Fahrenheit compared to today. By the year 2100, temperatures could increase by about five to ten degrees Fahrenheit.
Preparing for and preventing the worst of these future scenarios will be a challenge. New Yorkers need to act now to prevent a future of widespread coastal and inland flooding, dangerously hot summers, stressed water supplies and vanishing beaches. Most importantly, New Yorkers need to work to reduce their emissions of the gases that cause climate change and to support efforts at the national and international levels to assure that global warming is slowed and eventually halted.
Sea-Level Rise, Storm Surges and Coastal Hazards
As more heat is retained through the earth's atmospheric, oceanic, and terrestrial systems, ocean waters expand and many mountain glaciers melt. This process leads to higher sea levels which cause beach erosion, inundation and erosion of coastal wetlands and, in some cases, contamination with saltwater of coastal aquifers and other urban water supplies. With higher sea levels, small storms could produce large amounts of flooding, similar to that which strong, relatively infrequent storms produce today. The projected amount of sea-level rise may not seem particularly large -- it is estimated that sea levels in the New York Metropolitan Region will increase by 3/4 to 3 1/2 feet by 2100 -- but, when a storm hits, that small increase may be enough to swamp coastal areas.
A large part of lower Manhattan would be at risk from frequent flooding by the end of the next century according to these scenarios, even if storms did not become more intense or frequent. The foundations of Battery Park City and the World Trade Center would be flooded regularly. The East River would flood Bellevue Medical Center, the FDR Drive and East Harlem between 96th and 114th Streets. Storms would flood much of Coney Island, submerging or creating islands of residential communities there and in Staten Island nearly annually. In New Jersey, storm surges would temporarily transform the Meadowlands into a salty lake. During storm surges, the barrier islands of Long Island -- including Jones Beach, Fire Island, and Westhampton Beach -- could narrow and fragment into small islets, while highly productive saltmarshes could shrink permanently due to higher sea levels. Although marshes adapt to moderate rates of sea-level rise, they may be unable to keep up with the accelerated rates that are expected to occur as a result of human-induced climate change.
Human Health: Heat and Ozone
The health of New York City residents is vulnerable to extremes of climate. Higher temperatures due to global warming could lead to increases in heat-related mortality and health risks due to air pollution. The elderly, children and those already plagued with respiratory problems are the groups most at risk.
In New York City, heat-related mortality increases significantly on days when the temperature tops 90 degrees Fahrenheit. Models project that the number of days per year that surpass that temperature threshold could increase from an historical average of 13 to between 38 and 80 days per year by the year 2100. Since 1880, temperatures in New York have already risen an average of 4 degrees Fahrenheit, partly due to the urban heat-island effect. Even if temperatures increase no faster than they have over the last hundred years, the average number of days over 90 degrees would be 27 by the year 2100. Meanwhile, New York's population of senior citizens, the group most threatened by increased temperatures, is expected to grow by 21% between now and the year 2010. On the other hand, warmer winters could decrease illness and mortality due to extreme cold as the number of days below freezing drops by more than half in the warmest projections.
Much of the New York Metropolitan Region is listed in the "severe" category for nonattainment of EPA's National Ambient Air Quality Standards for ozone, the primary constituent of urban smog. Warming may exacerbate air pollution because higher temperatures increase ozone production. Ground-level ozone in high concentrations causes eye and nose irritation, coughing, and impaired lung function.
Water Supply System
Global warming may increase the frequency of extreme weather events, including both prolonged periods with little precipitation and periods of heavy downpour and snowfall, leading both to more droughts and more inland floods. Higher temperatures alone can lower water supply because increased evaporation from land and water surfaces leads to reduced runoff from watersheds. In one scenario, a drought of the severity that currently occurs about once every hundred years could occur every three to eleven years by the year 2100. In another scenario, droughts are less likely but wetter conditions could lead to an increase in the number of floods. Drought and sea-level rise could push saltwater on the Hudson River further upstream, possibly requiring costly adaptations to an important emergency pumping station located at Poughkeepsie used to supply water to New York City during drought emergencies. The impact to New York City water users will depend on the degree of variability and severity of the weather events, the amount of sea-level rise, how demand for water changes in the future, and on the effectiveness of institutional and infrastructural adaptations and planning efforts. Institutional changes and possibly substantial and costly infrastructure investments may be required to cope with these stresses.
Citizens and policymakers have a choice of three general strategies, or some combination of the three, to respongd to climate change. The first is to do nothing until some crisis or disaster forces action. While a common response, this strategy may ultimately be the cstliest and lead to the greatest threat to lives and assets. The second is to plan ahead and try to adapt to climate change through a range of activities -- from buying air conditioners to raising sea walls to retreating from shorefront property as beaches erode. In any event, a sbustantial amount of climate change and sea-level rise may occur due to greenhouse gases already emitted, for which adaption could be both costly and necessary.
However, a third possibility is available: the mitigation of climate change itself through the reduction of greenhouse gas emissions. Reducing emissions would also improve air and water quality now, by reducing ground-level ozone, particulate matter, acidic deposition, and eutrophication of local estuaries. In addition, by avoiding the worst of the scenarios described in this report, reducing emissions would lower the cost and severity of adaptation measures needed. Large uncertainties remain but reducing emissions now, on a personal, local, national, and international basis, can avert the most disruptive scenarios.