Record high US temperatures outpace record lows to one, study finds

The AP looked at 424 weather stations throughout the US lower 48 states that had consistent temperature records since 1920 and counted how many times daily hot temperature records were tied or broken and how many daily cold records were set. In a stable climate, the numbers should be roughly equal.

Since 1999, the ratio has been two warm records set or broken for every cold one. In 16 of the last 20 years, there have been more daily high temperature records than low.

The AP shared the data analysis with several climate and data scientists, who all said the conclusion was correct, consistent with scientific peer-reviewed literature and showed a clear sign of human-caused climate change. They pointed out that trends over decades are more robust than over single years.

The analysis stopped with data through 2018. However, the first two months of 2019 are showing twice as many cold records than hot ones. That’s temporary and trends are over years and decades, not months, said National Oceanic and Atmospheric Administration climate monitoring chief Deke Arndt.

"We are in a period of sustained and significant warming and over the long run will continue to explore and break the warm end of the spectrum much more than the cold end,” Arndt said.

Former Weather Channel meteorologist Guy Walton, who has been studying hot and cold extreme records since 2000, said the trend is unmistakable.

"You are getting more extremes,” Walton said. "Your chances for getting more dangerous extremes are going up with time.”

One stark example is the southern California city of Pasadena, where 7,203 days went by between cold records being broken. On 23 February, Pasadena set a low temperature record, its first since 5 June 1999.

Vermont native Paul Wennberg felt it. He moved to Pasadena in 1998 just before the dearth of cold records.

"Even with the local cold we had this past month, it’s very noticeable,” said Wennberg, a California Institute of Technology atmospheric sciences professor. "It’s just been ever warmer.”

In between the two cold record days, Pasadena set 145 hot records. That includes an all-time high of 113F last year.

"Last year was unbelievable here,” Wennberg said. "The tops of a lot of the hedges, they essentially melted.”

Scientists often talked about human-caused global warming in terms of average temperatures, but that’s not what costs money or sends people to the hospital. A study this month found that in just 22 states, about 36,000 people on average go to the hospital because of excessive summertime heat.

"The extremes affect our lives,” Arndt said, adding that they are expensive, with hospital stays, rising energy bills and crop losses.

The AP counted daily records across 424 stations starting in 1920 and ending in 2018.

The AP only considered daily not all-time high maximum temperatures and low minimum temperatures and only used stations with minimal missing data.

More typical than Pasadena is Wooster, Ohio. From 1999 on, Wooster saw 106 high temperature records set or broken and 51 cold ones. In the previous eight decades, the ratio was slightly colder than one to one.

In all, 87% of the weather stations had more hot records than cold since 1999. There have been 42 weather stations that have at least five hot records for every cold one since 1999, with 11 where the hot-to-cold ratio is 10-to-1 or higher, including Pasadena.