The Impact of Climate Change on Urban Environments
New York City and the tri-state region provide a unique case study for examining the impact of climate change within the context of an urban environment.
Published November 1, 2002
By Margaret W. Crane
Academy Contributor

In Alaska the average temperature has risen by 5.4 degrees Fahrenheit over the past 30 years, and entire villages are being forced to move inland because of rising sea levels. El Niño – a disruption of the ocean-atmosphere system in the tropical Pacific – has been linked with multiple epidemics of dengue fever, malaria and cholera. Flowers in the northern hemisphere are blooming in January. Greenland’s glaciers are melting. The world’s ecosystems are in the throes of rapid transformation. And large, coastal cities are among the most vulnerable of all.
Global by definition, climate change has already begun to reshape the earth’s environment from pole to pole and from tundra to rainforest. But until recently few scientists had studied its impact on cities. Cynthia Rosenzweig, PhD, the lead author of a recent report titled Climate Change and a Global City, is among the first to look at cities – specifically New York and its environs – as distinct ecosystems that are being remodeled by global warming as relentlessly as are distant oceans, islands, forests and farmlands.
At the Forefront of Vulnerability to Climate Change
Rosenzweig and co-author William D. Solecki place global cities like New York, Sao Paulo, London and Tokyo at the forefront of vulnerability to climate change. As such, the world’s largest cities are charged with finding ways to adapt to changes that have already occurred and simultaneously reduce the greenhouse gases that are a major factor in heating up the globe in the first place.
“Global warming is on the cusp of becoming a mainstream issue,” said Rosenzweig, “an issue that’s being integrated into the day-to-day life of citizens.” This mainstreaming is emerging in tandem with a stronger-than-ever consensus among scientists that climate change has arrived and has two faces: an overall warming trend, and more frequent and severe droughts and floods. Moreover, instead of hypothesizing about global warming, researchers are now studying its effects and developing models to project the course and intensity of future changes.
To map the trajectory of projected climate change, scientists are using global climate models (GCMs), mathematical formulations of the processes – such as radiation, energy transfer by winds, cloud formation, evaporation and precipitation, and transport of heat by ocean currents – that comprise the climate system. These equations are then solved for the atmosphere, land surface, and oceans over the entire globe.
Because GCMs take into account increasing feedbacks from greenhouse gases, they project more dramatic temperature changes than do predictions based on current warming trends alone. New York’s GCM-projected temperature in the 2080s, therefore, will be from 4.4 to 10.2 degrees Fahrenheit higher. Rosenzweig and Solecki predict a more modest 2.5 F rise by the 2080s, based on current temperature trends alone minus any multiplier effect associated with greenhouse gases.
Interchange Between Scientists and Decision-Makers
The Climate Change report draws on a range of GCMs, but it also benefits from a rich interchange between scientists and decision-makers. In grappling with the complexity of the urban ecosystem, the two groups developed an innovative conceptual framework comprising three basic, intersecting elements: People, Place, and Pulse. These three P’s correspond to socio-economic conditions, physical and ecological systems, and decision-making and economic activities. “Pulse, a term we coined, is really about what makes a city a city,” said Rosenzweig. “In the past few years, I’ve gotten on familiar terms with New York’s pulse, defined roughly as the whole matrix of relationships that makes it run and hum.”
Rosenzweig’s focus on the New York region began when she was chosen to head up the Metropolitan East Coast (MEC) Regional Assessment, part of a national effort to assess the potential consequences of growing climatic instability and the engine behind the Climate Change report.
The New York metropolitan region is unique, Rosenzweig said, due to the extraordinary density and diversity of its population. Comprised of five boroughs and 26 adjacent counties in New York, New Jersey and Connecticut, it is home to a complex web of environmental problems and pressures. The area’s high demand for energy and clean water, along with its poor air quality, toxic waste dumps and threatened wetlands, are all interconnected, according to the Assessment, and call for a many-sided response.
Rising Seas Levels and Floods
For instance, New York will likely need to build higher seawalls and raise airport runways to protect against rising sea levels and increasingly severe and frequent floods. City and regional governments will be called upon to increase support for the poor and elderly, who suffer disproportionately from heat stress and respiratory ailments due to the effects of air pollution. Developers will be encouraged to disinvest from highly vulnerable coastal sites. Policymakers will need to think longer-term and learn to cooperate at the regional level. And they’ll have to get serious about reducing greenhouse gas emissions.
But it is New York’s greatest virtue – its diversity – that turns out to be its political stumbling block. The 20 million people who inhabit the area’s boroughs and neighboring counties often represent conflicting agendas. Rosenzweig believes it will take education, training and a good dose of political will to take on global warming.
In recent decades, the MEC region has experienced a marked increase in floods, droughts, heat waves, mild winters and early springs. Its annual average temperature has risen by nearly 2 degrees Fahrenheit, and precipitation levels have gone up slightly. The current rate of sea-level rise is about 0.1 inch per year, a number that is expected to increase with the further melting of glacial ice and the warming of the upper layers of the ocean. The study found that in many scenarios, the sea level is expected to rise faster than the accretion rate of wetlands, further accelerating their disappearance.
Growing Hydrologic Variability
Growing hydrologic variability is another expression of the climate change that has already begun to be felt in the region. This century, the New York area will be subject to more severe flooding during hurricanes and nor’easters. Some scientists have estimated that by the 2080s, as a worst-case scenario, a major coastal storm could occur every three to four years, compared with every 100 years in the past, while a 500-year flooding event could hit every 50 years.
It has long been the region’s default policy to place transportation and other necessary but unappealing infrastructure across and along the edges of wetlands, bays and estuaries. For example, the Hackensack Meadowlands in northern New Jersey, a low-elevation, degraded wetland, is home to an airport, port facilities, pipelines and highways. The region will need to move infrastructure inland – a matter of double urgency, Rosenzweig contends, for the sake both of the infrastructure itself and the vulnerable lands that are the first casualty of violent storms.
Climate change is, however, a bipolar phenomenon. During the summer of 1999, an intense summer drought may have contributed to the fatal outbreak of West Nile virus. More conspicuously, water conservation campaigns have become a regular feature of New York life. While the New York City water supply system – the largest in the region and one of the largest in the world – should accommodate expected hydrologic extremes, the report warns that smaller systems within the MEC region might buckle under stress. Increasingly, water distribution must be addressed intra- and inter-regionally, said Rosenzweig. Future protocols might include diverting Delaware River water from the west to reduce the impact of drought in the New York area, and vice versa.
Multiplicity of Environmental Problems
Demand for electricity also is expected to rise along with mounting temperature. No less than clean and abundant water, the area’s population requires a consistent supply of energy. But the distribution of energy continues to be far from equal. During the intense succession of heat waves over the past several summers, blackouts and brownouts plagued many of New York’s poorer neighborhoods, meaning a loss of air conditioning just when it was most critically needed.
With 27 days of temperatures above 90 degrees Fahrenheit in the summer of 1999 and 28 days over 90 degrees F (including two in September) in the summer of 2002, New Yorkers have had a recent foretaste of what’s in store. According to most climate change scenarios, the average number of days exceeding 90 degrees F (13 days in our present climate) will increase by two to three times by the 2050s.
Despite their multiplicity of environmental problems, Rosenzweig believes cities have an important role to play in shaping the earth’s future. “New York has an opportunity to rethink itself as an urban ecosystem,” she said. “For example, we can start to design buildings that are more energy-efficient. We’ll need to find ways to help people stay cooler as they adapt to a warmer environment and to reduce greenhouse gas emissions at the same time.”
The Missing Link
Although scientists haven’t yet been able to establish to an absolute certainty the causal link between human activity – especially the burning of fossil fuels – and climate change, they are largely in agreement that such change is under way. The Intergovernmental Panel on Climate Change has concluded that “there is a discernible anthropogenic signal in the climate,” and that this signal is growing. There are, however, many remaining uncertainties surrounding the rate and ultimate magnitude of the change.
By assessing its nature and extent, monitoring its trajectory, and forecasting its future impact on cities, scientists like Rosenzweig are informing a new public discussion that is just getting off the ground. But there’s no time to waste, she said: “The political and social responses to the global climate issue in cities should begin at once.”
Also read: Tales in New Urban Sustainability
About Dr. Cynthia Rosenzweig
Dr. Cynthia Rosenzweig is a research scientist at the Goddard Institute for Space Studies, where she is the leader of the Climate Impacts Group. She is an adjunct senior research scientist at the Columbia University Earth Institute and an adjunct professor at Barnard College. A recipient of a 2001 Guggenheim Fellowship, Dr. Rosenzweig led the Metropolitan East Coast Region for the U.S. National Assessment of the Potential Consequences of Climate Variability and Change.
She is a lead author of the Intergovernmental Panel on Climate Change Working Group II Third Assessment Report, and has worked on international assessments of climate change impacts, adaptation and vulnerability. Her research focuses on the impacts of environmental change, including increasing carbon dioxide, global warming, and the El Niño-Southern Oscillation, on regional, national and global scales.