A new peer-reviewed study from Utah State and Taiwanese researchers concluded, “There was a detectable effect of anthropogenic [manmade] global warming in the physical processes that caused the persistent precipitation in May of 2015? over the southern Great Plains.”
We’ve known for a long time that global warming puts more moisture in the atmosphere, which in turn makes deluges more intense. And the 2014 U.S. National Climate Assessment found that Texas and Oklahoma — and indeed most parts of the country — have already seen an measurable increase in the most intense rain storms.
But the Geophysical Research Letters study found a much deeper link between human-caused climate change and the Texas floods. I asked the study’s lead author, Simon Wang of the Utah Climate Center, to explain the findings:
Basically, we linked the weather conditions that caused the consecutive and high amounts of rainfall to two main climate sources: (1) El Niño and its enhanced teleconnection owing to the warming Pacific temperature and (2) middle latitude circulation that is becoming increasingly “wavy,” causing the trough (or any ridge for that regard) to stick around for a long time.
The second conclusion — that climate change is causing weather patterns to stall — joins a growing body of research tying the recent jump in extreme weather to a warming-driven weakening of the jet stream and “more frequent high-amplitude (wavy) jet-stream configurations that favor persistent weather patterns,” as a January 2015 study put it.
The study explains some of the science underlying the first point about the link between global warming, sea surface temperatures (SSTs) and the El Niño Southern Oscillation (ENSO) in more detail:
A developing El Nin?o has a tendency to increase spring precipitation over the southern Great Plains and this effect was found to have intensified since 1980; this intensification was concomitant with a warmer atmosphere due to anthropogenic GHG. Specifically, the intensified ENSO teleconnection appears to be triggered by enhanced latent heating in the equatorial central Pacific, and is associated with broad SST warming in the tropics. In essence, there was a detectable effect of anthropogenic global warming on the teleconnection and moisture transport leading to May 2015’s high precipitation.
Wang emphasized the importance of the new research in improving climate forecasting: “Identifying (1) and (2) is crucial because this event (very wet May in TX-OK) was forecast 3 months earlier by operational climate forecast models.” But, Wang notes, “What wasn’t forecast is the extreme magnitude. It is an important progress by climate forecasting community! Knowing that El Niño impact will increase can potentially help (climate) forecasters better anticipate extreme events.”
The bottom line is that many different types of weather events — heat waves, droughts, and deluges — are getting more extreme and global warming is the primary reason.