This July is on track to be Earth’s hottest month ever recorded, and that spike in heat is part of a larger warming trend that could change the way governments and researchers measure extreme temperatures.

When it comes to triple-digit days in Austin, last century we averaged about 13 annually, but this century, we’re averaging 38 triple-digit days a year, according to Spectrum News Chief Meteorologist Burton Fitzsimmons.

"If we look at the average temperatures since spring 40 years ago, we’re 4 degrees warmer – in just 40 years," Fitzsimmons says. "That’s a scary and alarming rate."

The picture doesn't get any less alarming when you look at the heat index – the "feels like" temperature that combines heat and humidity to give a better sense of how we experience heat.

This week, the Union of Concerned Scientists (UCS) came out with a report saying that the average heat index temperature will continue to rise into this century.

The report finds that, if nothing is done about climate change, Austin may average one day a year where the feels-like temperature hits 127 degrees by the middle part of the century – anywhere from 2036 to 2065. That would rise to 12 days, on average, by the end of the century – between 2070 and 2099.

UCS researchers say that estimation is in line with current and historical growth patterns of greenhouse gas emissions.

The report refers to those high temperatures as "off the charts" because they "fall outside of the current chart of heat index used by the National Weather Service," says Astrid Caldas, a senior climate scientist with the UCS.

She says the current way the NWS measures heat index was created to account for 99 percent of weather conditions over 99 percent of the globe.

"You'd think that covers pretty much everything," Caldas says. "However, with global warming, the numbers are starting to creep up, so that formula cannot reliably be used to calculate values that are so high."

Caldas says governments at all levels need to begin treating heat as a public health question, providing cooling assistance programs and across-the-board occupational health standards.

"You have a lot of outdoor workers and these outdoor workers are going to be deeply affected by this extreme heat," she says.

Ultimately, research shows that the best path to slow, and eventually halt, global warming is to reduce greenhouse gas emissions, which would require a rapid transition away from fossil fuels to greener forms of energy.

If some action on climate change is taken and greenhouse gas emissions begin to decline by midcentury, UCS researchers predict, Austin would average only one day with a heat index above 127 degrees by the century's end.