It was a summer unlike any other in recent memory: Day after day of blistering heat, punctuated by fearsome Hurricane Harvey, which ravaged the Texas coast, and a rare, benevolent cold front that brought a taste of fall to September.
Underlying all of it, is the ongoing debate over how much climate change is contributing to a decadelong pattern of higher temperatures that are helping fuel increasingly powerful tropical storms.
“We’re starting to perceive and experience the long-predicted impacts of global warming,” said Kerry Cook, a University of Texas climate science professor. Cook, who began her career working in a National Oceanic and Atmospheric Administration lab at Princeton, has studied climate change and its possible effects for the last 35 years.
“Seeing is believing, I suppose,” Cook said. “I’m hoping this will put together the national will to help us do something.”
There was no doubt about the heat Austin faced this summer.
From June 1 through Aug. 31, the period meteorologists consider summer, the city clocked 42 days when temperatures hit — and often easily surpassed — the 100-degree mark. This year had the fifth-most 100-degree days among years with complete records, an American-Statesman analysis found.
“This was a hotter than normal summer; it ended up ranking as the seventh-hottest summer of all time,” based on the average high temperature, said Bob Rose, a meteorologist with the Lower Colorado River Authority. “The number of 100-degree days that we’ve seen over the last decade — they’ve been increasing.”
The record for the most 100-degree days is 90 set in 2011. While this year had almost half that number, it had nearly double the 24 days of triple-digit temperatures seen in 2015 and also in 2016.
It was hotter during the nights as well, said Cory Van Pelt, a National Weather Service meteorologist.
After 24 days of 100-degree temperatures in July alone and 15 more in August, Central Texas was drying out and parts of the area began to see signs of drought. Relief for Austin came from Harvey, the storm that tormented Houston with more than 50 inches of rain and caused massive flooding in towns east of Austin, including Smithville and La Grange.
In Austin, Harvey dropped 8 to 10 inches of rain over several days, which saturated the ground and helped to keep temperatures under control in September, Rose said. It also opened the door for a September cold front that knocked temperatures into the 80s and kept the humidity at bay for a week.
The combined effect of Harvey and that blissful week means that temperatures so far this September are running a degree lower than average, Rose said.
Historically, Austin summers were not always this hot. Out of the 115 complete years in National Weather Service records, 83 of them had 20 or fewer 100-degree days. Recently, the wet summer of 2007 had just three days of 100-degree weather.
But since 2010, each year has seen at least 21 days in which thermometers at Camp Mabry reached or breached the 100-degree mark — for a total of 300 days so far this decade.
During Austin’s second-hottest decade — 2000-2010 — Austin recorded 273 days, while the 1920s counted 215 days, making it the third-hottest. Austin weather records for two years in the 1920s, are incomplete, but records for Houston, Dallas and San Antonio show no 100-degree days during those missing months.)
“It indicates that we have moved into a hotter summer pattern here in Central Texas,” Rose said, who added that it is incredibly difficult to discern the exact cause.
Part of the answer, Rose said, might come from Austin’s growing size: More roads, more cars and more buildings are effective at trapping or generating heat.
“We’re looking at this as a decade or two-decade pattern, which is just a really short time scale,” Rose said. “It does appear there are a lot of factors at play here, it’s not just one thing or another.”
However, Cook is convinced there’s more than just the usual gyrations at play.
“There’s natural variability on decadelong time scales,” she said. “We have a physical understanding of how the climate system works. It’s not true that things just bounce around by magic.”
Van Pelt said he believes the intensifying heat is driven by a mixture of both.
“Get used to it,” Van Pelt said. “It’s basically what we’re going to be stuck with.”