A new study from The Earth Institute at Columbia University projects that heat-related fatalities could rise steeply in Manhattan by the 2020s as a result of a warming climate, and that in some worst-case scenarios, "by 90 percent or more by the 2080s." Researchers involved in the study, which will be published this week in Nature Climate Change, say that this is one of the most comprehensive city-specific studies conducted so far, with combined data from all seasons and application of multiple climate scenarios. "This serves as a reminder that heat events are one of the greatest hazards faced by urban populations around the globe," climate scientist and coauthor Radley Horton said.

The results add another data point to an overwhelming body of evidence that suggests the Earth's changing climate will pose a threat to human life in the coming decades. Earlier this year, climate scientists at NASA ranked 2012 as the ninth-warmest year since 1880, when annual temperatures were first recorded. (NASA's findings also indicated that the ten hottest years in this period have all occurred since 1998.) Scientists and climate advocates have worked to reduce greenhouse gas emissions, pegged as a key agitator of climate change, for many years. Recently, warnings have come from unexpected places; earlier this year, US national security advisor Tom Donilon said that climate change is a national security threat.

According to the new study from Columbia, Manhattan faces unique challenges as a densely populated area, with the increase in average monthly temperatures outpacing global and US trends. The study attributes this change in part to the fact that buildings and pavement in cities concentrate heat, absorbing it during the day and releasing it at night. The study projects that Manhattan will continue to see steep average increases in temperature: "3.3 to 4.2 degrees Fahrenheit more by the 2050s, and 4.3 to 7.1 degrees by the 2080s."

To calculate death estimates, researchers applied temperature projections from 16 global climate models — downscaling them to Manhattan — against two scenarios: one with rapid population growth and minimal efforts to limit emissions, and another assuming slower growth and a decrease in emissions by 2040 due to technological advancements. In both scenarios, the study projects that heat-related deaths will rise in the 2020s. Deaths are projected to be worse in May and September — periods the researchers say "will probably increasingly become incorporated into the brutal dog days of summer."