It's less than a month into the summer and triple-digit temperatures have already shattered records in many cities across the country, like around Los Angeles area where it hit 114 degrees in Burbank and 120 degrees in Chino on July 6.

That's as hot as last year's brutal summer when temperatures hovered around 120 degrees in Phoenix and prompted American Airlines to cancel more than 40 flights at its hub there. The regional jets that feed big airlines' couldn't operate with temperatures above 118 degrees. The extreme heat that has come with climate change is prompting airplane manufacturers to test their fleets for increasingly hotter temperatures.

While travelers are used to flight cancellations in blizzards, the unpredictable storms and extreme heat of warmer months present airlines — and passengers — with some of the most challenging conditions of the year. The gradual warming of the earth that has come with climate change is causing more frequent and more severe swings in weather patterns across the globe. That means more days of extreme heat that airlines didn't have to worry about before.

"Last summer was a wake-up call for us," said Ross Feinstein, a spokesman for American Airlines, the world's largest carrier by traffic.

Once the busy summer travel season was over, Feinstein said the airline approached Montreal-based Bombardier, the manufacturer of the regional jets that were grounded in the heat wave, to see if the planes could fly at higher temperatures.

The company won that approval from U.S. and Canadian regulatory agencies in May, said Bombardier spokeswoman Nathalie Siphengphet.

The maximum temperature at which Bombardier CRJs can fly depends on altitude, but from Phoenix, it's now around 123 degrees Fahrenheit, up from about 118. Bombardier's competitor, Brazil's Embraer has taken similar steps and its new E190 E2 regional jet, which started service this April, can operate at higher temperatures than previous models.

"Rising temperatures have been an important design consideration for Embraer," the company said in a statement.