NEW YORK -- New England's maple trees stop producing sap. The Long Island and Cape Cod beaches shrink and shift, and disappear in places. Cases of heatstroke triple. 

And every 10 years or so, a winter storm floods portions of Lower Manhattan, Jersey City and Coney Island with seawater.

The Northeast of recent historical memory could disappear this century, replaced by a hotter and more flood-prone region where New York could have the climate of Miami and Boston could become as sticky as Atlanta, according to the first comprehensive federal studies of the possible effects of global warming on the Northeast.

"In the most optimistic projection, we still end up with a six- to nine-degree increase in temperature," said George Hurtt, a University of New Hampshire scientist and co-author of the study on the New England region. "That's the greatest increase in temperature at any time since the last Ice Age."

Commissioned by Congress, the separate reports on New England and the New York region explore how global warming could affect the coastline, economy and public health of the Northeast. The language is often technical, the 
projections reliant on middle-of-the-road and sometimes contradictory predictive models.

But the predictions are arresting. New England, where the regional character was forged by cold and long, 
dark winters, could face a balmy future that within 30 to 40 years could result in increased crop production but also destroy prominent native tree species.

"The brilliant reds, oranges and yellows of the maples, birches and beeches may be replaced by the browns and dull greens of oaks," the New England report concludes. Within 20 years, it says, "the changes in climate could potentially extirpate the sugar maple industry in New England."

The reports' origins date to 1990, when Congress passed the Global Change Research Act. Seven years later, the Environmental Protection Agency appointed 16 regional panels to examine global warming, and how the nation 
might adapt. These Northeast reports, completed about two months ago, are among the last to be released. (The mid-Atlantic report, which includes Washington, was completed a year ago.) 

The scientists on the panels employed conventional assumptions, such as an annual 1 percent increase in greenhouse gases in the atmosphere. They conclude that global warming is already occurring, noting that, on average, the Northeast became two degrees warmer in the past century. And they say that the temperature rise in the 21st century "will be significantly larger than in the 20th century." One widely used climate model cited in the report predicted a six-degree increase, the other 10 degrees. 

The Environmental Protection Agency summarizes the findings on its Web site.

"Changing regional climate could alter forests, crop yields, and water supplies," the EPA states. "It could also threaten human health, and harm birds, fish, and many types of ecosystems." 

Yale economist Robert O. Mendelsohn is more skeptical. He agrees that mild global warming seems likely to continue -- but argues that a slightly hotter climate will make the U.S. economy in general, and the Northeast in 
particular, more rather than less productive. A greater risk comes from spending billions of dollars to slow emissions of greenhouse gases. "Even in the extreme scenarios, the northern United States benefits from global warming," said Mendelsohn, editor of the forthcoming "Global Warming and the American Economy." "To have New England lead the battle against global warming would be deeply ironic, because it will be beneficial to our climate and economy."

The scientists on the Northeastern panels estimated that Americans have a grace period of a decade or two, during which the nation can adapt before global warming accelerates.

"We will face an increasingly hazardous local environment in this century," said William Solecki, a professor of geography at Montclair State University in New Jersey and a co-author of the climate change report covering the New York metropolitan region. "We're in transition right now to something entirely new and uncertain."

Heat Island

New York City, the nation's densest urban center, is armored with heat-retaining concrete and stone, and so its median temperature hovers five to six degrees above the regional norm. The city, the New York report predicts, will grow warmer still. Within 70 years, New York will have as many 90-degree days a year as Miami does now.

If temperatures and ozone levels rise, the report says, the poor, the elderly and the young -- especially those in crowded, poorly ventilated buildings -- could suffer more heatstroke and asthma. 

But such problems might have relatively inexpensive solutions, from subsidizing the purchase of air conditioners to planting trees and painting roofs light colors to reflect back heat.

"The experience of southern cities is that you can cut deaths and adapt rather easily," said Patrick Kinney of the Mailman School of Public Health at Columbia University, who authored a section of the report. 

Rising ocean waters present a more complicated threat. The seas around New York have risen 15 to 18 inches in the past century, and scientists forecast that by 2050, waters could rise an additional 10 to 20 inches. By 2080, storms with 25-foot surges could hit New York every three or four years, inundating the Hudson River tunnels and flooding the edges of the financial district, causing billions of dollars in damage. 

"This clearly is untenable," said Klaus Jacob, a senior research scientist with Columbia University's Lamont-Doherty Earth Observatory, who worked on the New York report and is an expert on disaster and urban infrastructure. 
"A world-class city cannot afford to be exposed to such a threat so often."

Jacob recommends constructing dikes and reinforced seawalls in Lower Manhattan, and new construction standards for the lower floors of offices. Sea-level rise could reshape the entire Northeast coastline, turning the summer retreats of the Hamptons and Cape Cod into landscapes defined by dikes and houses on stilts. Should this come to pass, government would have to decide whether to allow nature to have its way, or to spend vast sums of money to replenish beaches and dunes. Complicating the issue is the fact that some wealthy coastal communities exclude nonresident taxpayers from their beaches.

"Multimillionaires already are armoring their property with sandbags, but they can't do it on their own," said Vivian Gornitz of Columbia's Center for Climate Systems Research, author of the report's section on sea rise. "You would be asking taxpayers to pay for restoring beaches they can never walk on, and they might demand access."

Mild New England

Farther north, global warming could change flora and fauna, and perhaps the culture itself.

Compared with a century ago, the report notes, ice melts a week earlier on northern lakes. Ticks carrying Lyme disease range north of what scientists once assumed was their natural habitat. Moist, warm winters have led to 
large populations of mosquitoes, with an accompanying risk of encephalitis and even malaria.

"The present warming trend has led to another growing health problem," the report states, "in the incidence of red tides, fish kills and bacterial contamination." 

Hot, dry summer months, the report continues, "are ideal for converting automobile exhaust . . . into ozone." Because winds flow west to east, New England already serves as something of a tailpipe for the nation. The report notes that a study of ozone pollution and lung capacity found that hikers on Mount Washington, New Hampshire's highest peak, ended their treks in worse condition than when they started.

These findings are not definitive. Rising temperatures could exacerbate the effects of harmful ozone -- but anti-pollution laws are also cutting emissions.

"There is a little tendency to be alarmist in global warming studies," Kinney said. "We could keep ozone in check."

A warmer New England could help some economic sectors. As oak and hickory replace maples and birch, so commercial forestry might grow. Shorter winters could translate into longer growing seasons, lower fuel bills and 
less money spent on frost-heaved roads. The foliage and ski industries would suffer, but lingering autumns could bring more tourists and dollars to the coastal towns of Maine and Massachusetts.

"People complain that we'll lose the sugar maple, but 100 years ago, New England was 80 percent farmland," said Yale economist Mendelsohn. "In fact, an entire landscape has shifted in the past 100 years, and most people have no idea it was once so different."

Perhaps -- though cold has defined New England for almost 400 years, and some historians caution that the cultural shift could prove disorienting. The region reflects its climate; the literature is austere, the houses stout. For the 19th century naturalists of the region, a clammy southern heat represented moral slackness.

"Surviving winter has become our self-selecting filter," said Vermont archivist Gregory Sanford. "What will we brag about if we live in a temperate zone and go around in Hawaiian shirts and sandals?"

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