Dangerous heat days are likely to increase two- to four-fold across Maine by 2050, forcing towns and cities to reconsider how workers and aging and homeless residents survive increasingly volatile summers, according to a state health report released Friday.

The extreme temperature survival manual predicts a sharp rise in the number of life-threatening days with a heat index of 95 degrees or more by 2050. In Lewiston, five dangerous days a year will likely turn into 15. In Portland, four dangerous days will likely become 13.5.

This rapid warming — which scientists know is caused when heat-trapping gases released by the burning of fossil fuels capture the sun’s energy in our atmosphere — creates a dangerous paradox for a state traditionally built for the cold.

While heat is now the leading weather-related killer nationally, Maine’s data shows cold-related illnesses still send more people to the emergency room than heat. On average, 330 residents visit the emergency room every year for cold-related illnesses, compared to 216 for heat.

State officials are now pushing a double-threat resilience model, with the report urging Mainers to think like a “hot-weather state” without lowering their guard against a winter likely to be more volatile than in years past.

Maine’s summers are already hotter than they used to be. We are 3.5 degrees above the historical average, with projections that it could be 10 degrees higher by the end of the century, according to data from the Maine Climate Council.

Residents of cold-weather states like Maine feel the health effects of heat at lower temperatures than those in hotter states, a 2015 Harvard University study found. Yet most do not believe local heat waves to be dangerous, according to a 2019 study from Yale University.

In the report, the state is introducing new ways to measure when outdoor work becomes deadly.

The guidebook debuts the “wet bulb globe temperature,” an experimental metric specifically for farmers, loggers and athletes that factors in solar radiation and wind to measure true heat stress on the human body. Maine’s outdoor workforce has a limited ability to regulate its environment.

The report offers guidance, but no mandates: the ultimate decision on how to protect residents remains entirely in local hands. There is no rule on when to open a cooling or a warming center; instead, the report offers towns a menu of response actions and suggested temperature triggers.

This local-first approach places the burden of emergency response on cash-poor municipalities.

The report identifies municipal buildings — libraries, town halls, and schools — as the primary local choice for cooling and warming centers. However, the report notes many lack the backup power and adequate heating and cooling equipment to be effective.