As the weather in New York City creeps back toward summer-like temperatures, a bit of warning: Enjoy it while you can. By the 2080s, Manhattan could see as many as 91 percent more heat-related deaths thanks to global warming.
Scientists from Columbia University created projections for the affect on mortality, month by month, of temperature increases under various warming scenarios. Below are the mean projections for the 16 models, under lower emissions and higher emissions scenarios.
If you're curious what that means in raw numbers, the researchers can answer that, too. If the population of Manhattan remains the same, the worst-case scenario 70 years from now will mean 250 more temperature-related deaths each year. A small fraction of the population — but a huge increase in effect.
By the 2020s, the mean projection is that the number of temperature-related deaths will increase 5.3 percent over 1980s figures, under a low emissions scenario. That's the result of heat-related deaths going up 21 percent and cold-related deaths dropping 12 percent. (The net change is calculated from the net change of each model.) That's a drop of about 50 cold-related deaths a year — and an increase of about 100 heat-related ones.
By the 2050s, that's changed substantially. Under the lower emissions model, deaths will increase 11 percent annually — or 15 percent under faster warming.
And by the 2080s, assuming a worst-case warming scenario, 31 percent more people will die each year for temperature-related reasons — with the number of people dying from heat almost doubling to about 1,000 people.
Manhattan served as an interesting case study for the effects of climate change primarily because of its density and historical record. From the university's overview:
Daily records from Manhattan’s Central Park show that average monthly temperatures already increased by 3.6 degrees 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 its warmest year on record, and in each of the past three years, it has seen temperatures at or above 100 degrees F. Projections for the future vary, but all foresee steep future average increases : 3.3 to 4.2 degrees F more by the 2050s, and 4.3 to 7.1 degrees by the 2080s.
(Last year, the National Weather Service created charts showing record high and low temperatures in Central Park. The last record low at that point had been set in 2004; there were 29 record highs in the interim.)
The researchers used 16 different climate models — mathematical tools developed to predict the effect of warming — and two emissions scenarios — anticipating either slow population growth and rapid emissions cuts or the opposite — to generate predictions for the warming effect on Manhattan. They then used that data to calculate temperature-related deaths. During the 1980s, just over 700 people a year died from excessive heat or cold. As winter months get warmer, the number of cold-temperature-related deaths will decline. But when the summers get hotter, the number of warm-temperature-related deaths will increase. The net effect in every scenario is more deaths.
Those deaths won't be uniformly distributed. As the report summary notes:
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.