It's getting hot in here 

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This past weekend, temperatures in Rochester approached 95 degrees, though the high humidity levels made it feel hotter than 110. Mayor Lovely Warren declared a Cool Sweep Heat Emergency, keeping city pools and spray parks open later and inviting residents to cool off in air-conditioned rec centers and city libraries. County officials extended hours at Ontario Beach Park.

It’s a Rochester July, and hot, humid days are to be expected. But when temperatures get high and the air gets muggy, the conditions pose serious risks for children, the elderly, people with cardiovascular conditions, and people who have to perform strenuous work outdoors or in uncooled environments. The National Weather Service developed the heat index — a calculation that uses temperature,  humidity, and whether it's sunny to quantify what it really feels like outside — to help people know when hot weather is dangerous.

Sweltering weather like that of this past weekend is going to become more frequent in the future, says a new report from the Union of Concerned Scientists, an environmentally minded scientific think tank. The report projects that in the mid and late century, Monroe County is going to see more days with a high heat index: days that are dangerously hot and humid, in plainspeak.

Researchers looked at every county in the US, and the upward trend will affect all of them, the report says. They projected midcentury and late-century increases under three different scenarios, each based on whether the US and other countries do something to cut climate-disrupting emissions:

• A no-action scenario, where emissions continue to rise, leading to an 8 degree increase in global average temperatures;
• A slow-action scenario, where emissions increase before they start to decrease midcentury, and where global average temperatures increase by 4.3 degrees;
• A rapid-action scenario where, in line with the 2015 Paris agreement, emissions are cut aggressively and global average temperatures rise by 3.6 degrees.

No matter the scenario, Monroe County is looking at a substantial increase in very hot days.
Between 1971 and 2000, the county experienced an average of eight days a year where the heat index surpassed 90 degrees Fahrenheit. The researchers project that by midcentury, a period they define as 2036–2065, the county would see:

• 39 days a year where the heat index exceeds 90 degrees if no action is taken on climate change. Of those days, 12 would exceed 100 degrees on the index.
• 29 days a year where the heat index exceeds 90 degrees if there's slow action on climate change. Of those days, six would exceed 100 degrees on the index.
• The numbers are even more drastic in the late century, which the report defines as the period from 2070 to 2099. Researchers project that Monroe County would see:
• 71 days a year where the heat index exceeds 90 degrees if no action is taken on climate change. Of those, 32 would exceed 100 degrees on the index, 19 would exceed 105 degrees on the index, and 2 would have "an off-the-charts heat index."
• 38 days a year where the heat index exceeds 90 degrees if slow action is taken on climate change. Of those, nine would would exceed 100 degrees on the index, and three would exceed 105 degrees on the index.

The rapid-action projections are the same for midcentury and late century: Monroe County would experience 31 days a year where the heat index exceeds 90 degrees, six of which would exceed 100 degrees on the index.

The increases are substantial under any of the scenarios, and they'll have wide-ranging implications, all of which are likely to play out in Monroe County. For example, hotter days will likely drive up energy use and household energy costs, thanks to air conditioning.

Extreme heat is also a socioeconomic issue. While many people will be able to find relief in air-conditioned homes, many others can't afford to buy and run AC units. Fans get you only so far when it's 95 and muggy, and those conditions can lead to dehydration and heat-related illnesses like heat stroke.

Programs like the city’s Cool Sweep help residents find relief. The city budgeted $11,800 for the program this year, which city spokesperson Justin Roj says are “relatively minor costs to provide relief from the heat and fun for our residents.”

The number of Cool Sweep days vary each year, from seven in 2015 and five in 2017 to 25 in 2016 and 19 in 2018. But logically, if the city sees an increase in very hot days, officials may have to bump up the budget.

But Cool Sweep or extended swimming hours at county and state beaches do have benefits beyond comfort. The longer people’s bodies are exposed to hot weather, the greater their risk for complications such as heat cramps, dehydration, and heat stroke. The programs provide public health benefits, as do things like New York’s Home Energy Assistance Program, which helps low-income New Yorkers cover heating and cooling costs.

As Monroe County and New York gets warmer, these programs will become more valuable.

This article has been update to match the version appearing in the July 24 print edition.