Residents of Manhattan will not just sweat harder from rising temperatures in the future, says a new study; many may die.

Researchers at Columbia University estimate deaths linked to warming climate may rise some 20 percent by the 2020s, and, in some worst-case scenarios, 90 percent or more 70 years hence.

Higher winter temperatures may partially offset heat-related deaths by cutting cold-related mortality, but even so, scientists say annual net temperature-related deaths might go up a third.

The study, published this week in the journal Nature Climate Change, was done by a team at the school's Earth Institute and the Mailman School of Public Health.

Studies of other cities have already projected adverse health effects from rising temperatures.

"This serves as a reminder that heat events are one of the greatest hazards faced by urban populations around the globe," said coauthor Radley Horton, a climate scientist at the Earth Institute's Center for Climate Systems Research.

The record 2010 heat wave that hit Russia, killing some 55,000 people, and the 2003 one in Europe that killed 70,000 are potent examples of the devastation that extreme heat can cause, Horton added.

Daily records from Manhattan's Central Park show that average monthly temperatures increased by 3.6º Fahrenheit from 1901 to 2000 – substantially more than the global and U.S. trends. Cities tend to concentrate heat; buildings and pavement soak it up during the day and give it off at night.

Many records have been set in Manhattan recently. 2012 was the borough's warmest year on record; in each of the past three years, it has seen temperatures at or above 100ºF. Projections for the future vary, but all foresee steep future average increases of 3.3ºF to 4.2ºF by the 2050s, and up to 7.1ºF by the 2080s.

Assuming Manhattan's current population of 1.6 million remains the same, the worst-case scenario translates to more than 1,000 annual deaths.

The study also found that the largest percentage increase in deaths would come not during the traditionally sweltering months of June through August, but rather in May and September – periods that are now generally pleasant, but which will probably increasingly become incorporated into the brutal dog days of summer.

Senior author Patrick Kinney, an environmental scientist at the Mailman School and Earth Institute faculty member, cautioned that things could be made better or worse by demographic trends and by how well New York adapts its infrastructure and policies to a warmer world.

New York is already a leader in efforts to mitigate warming, by planting trees, making surfaces such as roofs more reflective and opening air-conditioned centers where people can come to cool off. Even as city heat rose during the latter 20th century, some evidence suggests that heat-related deaths went down, Kinney noted, probably due to the introduction of home air conditioning.

"This points to the need for cities to look for ways to make themselves and their people more resilient to heat," he said.

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.