There’s a lot to say about the flash flooding that began last weekend in Texas and Oklahoma. So far 18 people are confirmed dead and at least 10 are missing. The weather’s broken records: Oklahoma City broke its all-time rainfall record for a single month, and Texas’ Wimberley Valley saw the highest flood in its recorded history. And more heavy rain is on the way.
Texas and Oklahoma are certainly no strangers to intense flooding, particularly in May, and particularly with an El Niño developing. But with average atmospheric carbon dioxide at levels so high that they’ve never before seen by humans, many have asked the question: what’s the role of human-caused climate change here?
The scientists ThinkProgress spoke to on Wednesday would not say the extreme flooding event was caused by climate change, noting the science of figuring out humanity’s role in a weather event would likely take about a year. But they agreed that current global warming has already made it more likely for an extreme flooding event like the one in Texas and Oklahoma to occur, and that similar events would become even more likely in a warmer world.
“There are several factors that have created conditions that made it more likely to have this disastrous situation, and I would say the majority of them are natural factors,” said Brenda Ekwurzel, a senior climate scientist with the Union of Concerned Scientists. “However, there’s a definite climate assist that creates the likelihoods of the odds of it being a more severe event.”
According to Ekwurzel, there were three basic contributors that made an intense flooding event more likely in the region, two of which had to do with our increasingly hot oceans. As Ekwurzel put its it, hot oceans can fuel extreme precipitation events because “the earth likes to cool itself off — so we end up having evaporation from the hot ocean’s surface, they form clouds, come over land, and they rain.”
Right now, she noted, there are above-average sea surface temperatures in the Gulf of Mexico and in the Pacific Ocean, the latter of which is being fueled by a building El Niño. That El Niño is expected to accelerate the effects of global warming even further.
The third factor that Ekwurzel said contributes to making a similar flooding event more likely in Texas and Oklahoma is one followers of the climate and weather connection know very well: the atmosphere’s ability to hold more moisture. The fact that the atmosphere is warmer because of increased carbon emissions means it’s able to hold more moisture, meaning more precipitation when storms occur.
“Because of climate change we have a very warm atmosphere,” Ekwurzel said. “And when you have a hot atmosphere you can hold more water vapor, so when a natural storm comes, you can organize that water vapor into a storm, wring out the atmosphere, and have very intense precipitation.”
Though it’s normal for Texas and Oklahoma to see torrential rainfall in the spring, one thing that’s been unusual is the duration of the event, according to Tom Di Liberto, a meteorologist at the National Oceanic and Atmospheric Administration’s Climate Prediction Center. Di Liberto told ThinkProgress that storms have been moving very slowly across the region, meaning that rain has been pummeling down day after day with little relief.
“It’s not unusual for these types of storms to develop and cause heavy amounts of rain. That’s normal — that’s springtime,” he said. “What’s been weird about this one is this pattern consistent throughout the month where we have these upper level systems that track very slowly … there’s just all these ingredients that lead to some areas getting a ton of rainfall in a very short amount of time.”
And with the area on the heels of recovering from one of its most severe droughts on record, he said, “It’s a little bit of a weather whiplash.”
Di Liberto said he wasn’t sure what exactly climate change’s role was in the current flooding events, but did note that climate scientists have seen an observed change in heavy precipitation across the United States. Indeed, the 2014 National Climate Assessment (NCA) predicts that climate change will increase the probability of extreme rainfall and flooding events in the Northeast, Midwest, and Great Plains. In the Great Plains, this will likely happen alongside more extreme droughts, the NCA predicts.
“You probably can’t tell from this individual event, what the impact of climate change was,” Di Liberto said. “But it’s not inconsistent with what you’d see in a warming world.”