By taking steps now to cut emissions, New Yorkers could prevent 300 of these expected deaths annually, Knowlton says. "We can save lives by taking progressive action now to regulate greenhouse gas emissions. That's the good news."

Knowlton and her colleagues used a computer model to estimate temperature increases in New York City and its environs by 2050 based on two scenarios, one representing rapid population growth and lack of "aggressive" greenhouse regulation, the other based on slower growth and "increased concerns about environmental sustainability."

By 2050, heat-related deaths would increase by 95 percent a year based on the worst-case, high-emissions scenario, a figure reduced to 68 percent when the researchers accounted for acclimatization to the heat with increased air conditioning, heat alerts and other adaptations. Under the lower emissions projection, deaths would increase by 71 percent, or 47 percent with acclimatization.

Knowlton and her colleagues found a dramatic variation in expected mortality increases across the region, ranging from 38 percent to 208 percent. The smallest increases would be seen in the more urban parts of the region, such as within the city itself and in the New Jersey suburbs to the west, which are already relatively warm and will experience smaller temperature increases.

But deaths could skyrocket in the suburban and rural New York and Connecticut counties north of the city, which are currently relatively cool.

"The urban areas, the suburbs, and the countryside are all going to be affected by these hotter temperatures," Knowlton said. No matter where they live, she added, poor people will likely have a tougher time coping with rising temperatures, given that many may not have air conditioning, or may be reluctant to use it due to electrical costs.

According to Knowlton, the best and fairest approach to reducing excess heat deaths due to global warming will be to introduce strong regulation of greenhouse gas emissions as soon as possible. "That kind of regulation is going to afford us the strongest prevention in an equitable way."