The number of sweltering summer days will only increase as climate change takes its toll on Kentucky, according to a study released Tuesday.

To understand just what the mercury rising might feel like, researchers from the Union of Concerned Scientists analyzed a century’s worth of data for temperatures and humidity to create a heat index, or, the “feels like” temperature often described in weather forecasts.

Without reductions in climate-change inducing greenhouse gases, the report warns the number of days when the heat index exceeds 100 degrees could double across the country by 2050 and quadruple by the end of the century.

“We know extreme heat is increasingly putting people at risk and will affect people across the country, which is unlike a lot of other climate impacts that can be more localized,” said Rachel Licker, senior climate scientist with the Union of Concerned Scientists.

Heat is one of the top weather-related causes of death in the U.S. and is particularly dangerous for sensitive groups including children, older adults and people with heart and lung conditions.

By the end of the century, the southeastern U.S. is expected to be hardest hit with nearly 100 days per year where the temperature feels like it’s above 100 degrees.

In Kentucky, only about six days per year are classified as having a heat index above 100 degrees right now, but that could reach 45 days by 2050 without global carbon reductions — and 76 days by 2100, according to the report.

Worse yet, Licker said Kentuckians may have to endure about 10 days of temperatures that could exceed 127 degrees by the end of the century.

“We use the National Weather Service’s heat index calculation to calculate head index temperatures across the country,” she said. “The equation falls apart above 127 degrees Fahrenheit and so we found in some parts of the country there will be days that are literally off the charts.”

Researchers looked at three possible scenarios for future carbon emissions in line with last year’s United Nation’s report on climate change. Assuming “business as usual” researchers found global average temperatures could rise about 8 degrees above pre-industrial levels by the end of the century.

With some action to reduce carbon emissions, they predict the increase is limited to 4.3 degrees, and even if the planet were to meet the guidelines of the Paris Agreement, the analysis still expects temperatures to rise about 3.6 degrees.

In the best case scenario, Kentucky can expect to see about 33 days with a heat index above 100 degrees.

Louisville, Bowling Green and Owensboro are expected to experience the highest number of days with a heat index above 100 degrees, according to the report.

And that’s without taking the urban heat island effect into account. The urban heat island phenomena occurs when impervious surfaces like pavement and asphalt absorb heat during the day and radiate it back causing cities to be hotter than surrounding natural areas.

As a result, it’s possible the study underestimates how hot it will become in cities, Licker said.

“We looked at changes in extreme heat as a result of global warming. We didn’t look at changes in extreme heat because of land use,” she said.

But both urban and rural communities have unique vulnerabilities when it comes to feeling the heat. People who work outside, for example, are looking at potential health and economic losses because of high temperatures.

But Licker said the worst can still be avoided, if the world can limit warming to 3.6 degrees.

Applying a price that reflects the true cost of carbon emissions, low-carbon energy standards and building community resilience are among the things we can do to avoid the worst-case scenario, she said.

“There’s a lot of power in the decisions we make today,” Licker said. “What we do today can help craft a future for children and grandchildren and even ourselves to be safer.”

To conduct the analysis, researchers from the Union of Concerned Scientists worked with the same climate models used in the Fourth National Climate Assessment and last year’s United Nations report on climate change. The scientists averaged projections from 18 climate models to calculate the number of high heat-index days from April through October for every state except Alaska and Hawaii.