A ‘climate feedback loop’: Why Austin is locked in one of its hottest summers ever

This summer has been among the hottest and hardest in memory. Austin broke an all-time heat index record in June when the “feels like” temperature topped off at 118 degrees. Then, we had our hottest July ever recorded.

This week, only halfway through August, it looks like we’ll surpass 40 days straight of triple-digit heat. This could end up being our hottest summer ever.

For many, the experience has been all the more difficult because last year was also incredibly hot. Early signs were that this year would be better. So, what happened?

A springtime fake-out

It’s hard to remember now, but spring was cool and rainy in Austin.

Not only was it downright pleasant, it was also encouraging. Moisture usually acts like a cushion against high temperatures, because the early summer sun will evaporate the water in the ground instead of heating things up.

On top of wet conditions, an El Niño was starting to form in the Pacific Ocean. This climate pattern affects weather differently depending on where you live. In Texas, it has typically meant we’re less likely to get a super hot summer. Until this year, none of the 10 hottest summers in Texas were during an El Niño.

That’s why in the spring, you’d even hear some forecasters saying we were likely to get a cool summer.

Not everybody was that confident. The National Weather Service predicted a warmer than average Texas summer. But the wet spring and El Niño led most to believe this year would, at least, be cooler than 2022, which brought our second-hottest summer on record.

Then the heat dome arrived.

A heat dome is a weather condition that traps hot air over a certain location. This year, that air was heated by warm Gulf waters and ground temperatures in Mexico when it moved over Texas in mid-June. That air heated up even more as it sank to the earth, evaporating the spring rainwater that had soaked the ground.

That led to record-breaking heat index readings in many cities. But it also did something else: It took away our cushion against the summer heat.

“My fear going forward,” National Weather Service Meteorologist Victor Murphy told KUT in June, is that “the longer this heat dome lasts, the ground starts getting dry, and then the heat takes off on its own – regardless of the presence of a heat dome or no heat dome.”

His fear came true. The June heat dome burned through the water in the soil, the very thing that was going to be our insurance against extreme summer heat. Once that water was gone, the summer sun began to bake the ground and heat the air.

There was nothing else to absorb the sun’s energy, and the weather stayed hot because, well, the sun is hot.

Hot and dry

“Basically, we transitioned from a weather-driven heat wave in Texas to more of a climate-driven heat wave,” John Nielsen-Gammon, the state climatologist, said on a July 20 conference call with the National Oceanic and Atmospheric Administration. “The high temperatures and lack of rain have dried out the soil. Now the sun’s heat heats the ground and heats the air without any energy being diverted to evaporation.”

Once this kind of heat starts, the process can become self-reinforcing. Nielsen-Gammon described it as a “climate feedback loop,” in which heat creates the conditions for more heat, which creates conditions for more heat, which creates … you get the idea.

“With less water available to evaporate, there’s less water in the air to form clouds and precipitation,” he said. “That means that the water in the ground is not replenished, and so if things get on the dry side, they tend to dry out even more.”

“That feedback has been triggered by that heat wave back in June,” he added. “Now that things are dry, they’re more likely to stay dry and hot.”

And they have.

Living the climate crisis

This explains the mechanisms that got us one of our hottest summers ever. But what about the big picture? How confident can we be that climate change contributed to this heat?

Very confident.

“With temperatures having increased in Texas by about 2 degrees Fahrenheit since the 1970s because of climate change, we can say that temperatures during this heat wave are about 2 degrees warmer than they would have been,” Nielsen-Gammon said in that July conference call.

Other studies have suggested that human-made climate change raised the temperature of the June heat dome by 5 degrees.

That’s important, because it was the heat dome that set the table for the rest of the summer.

“Because of the higher temperatures, we get more rapid evaporation of water. And that feedback mechanism I talked about kicks in sooner,” Nielsen-Gammon said. “Temperatures get hotter, faster.”

Researchers have pointed to other ways climate change may have contributed to our searing summer. But, even without itemizing exactly how global warming, well, warms us, it seems statistically certain that it is doing so.

Simply put, we’ve heard from researchers who for years have said this type of heat will become more common as we keep burning fossil fuels. People have been studying the impacts of greenhouse gas emissions long enough to understand that we’re living in the future we forecasted.

“In the past, these events would have been extremely rare … but now they are not rare,” Friederike Otto, a climatologist with a group called the World Weather Attribution, said. “We still continue globally to burn emissions at an increasing rate, so it is not a surprise to see the (climate) responses faster and faster.”

This means that we’re going to get hotter summers until we reduce emissions from fossil fuels. If that’s too depressing for you, it’s worth remembering that – while the trend is terrifying – it doesn’t mean every summer is going to be this bad or worse.

Next summer could always be better than this one. Of course, that’s what we said last summer.

This story was produced as part of the Austin Monitor’s reporting partnership with KUT.

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