As the seemingly endless barrage of violent tornadoes continued to pummel a large swath of the United States this week, lawmakers and concerned citizens declared on social media that the storms offered a front row seat to the unfolding climate crisis.

During a presidential campaign stop in disaster-stricken Iowa, Sen. Elizabeth Warren (D-Mass.) posted a video in which she says planetary warming is helping drive severe weather events, including tornadoes, and blasts those who deny the reality of climate change for “putting us all at risk.” In a post to Twitter, Sen. Bernie Sanders (I-Vt.), another 2020 contender, slammed the Trump administration for working to undermine climate science as sections of the central United States reel from tornadoes and catastrophic flooding. And when Washington, D.C., was put under a tornado warning May 23, Rep. Alexandria Ocasio-Cortez (D-N.Y.) posted to Instagram: “The climate crisis is real, y’all.”

The scientific community has long warned that anthropogenic climate change exacerbates extreme weather events, including tropical cyclones, heat waves, droughts and heavy rainfall. But the influence of human activity on tornadoes remains less clear.

That’s in part due to a limited amount of historical data. Unlike temperature and hurricane records, which date back more than a century, reliable tornado records go back only a few decades. Twisters are also short-lived, making it difficult to study individual events and detect trends.

Yet, even with these shortfalls, there is evidence that our changing climate may be leaving a mark, causing clusters of tornadoes and a shift in range.

“While there is some debate within the scientific community about the details of how climate change will impact tornadoes, there is increasing evidence that a warming atmosphere ― with more moisture and turbulent energy ― favors increasingly large outbreaks of tornadoes, like the outbreak we’ve witnessed over the past few days,” Michael Mann, a climate scientist at Pennsylvania State University, said by email.

In other words, planet-warming greenhouse gases could be helping to drive the storms that ultimately set the stage for tornado development.

The 4th National Climate Assessment, a congressionally mandated federal report released late last year, concluded that tornadoes have “become more variable” and are among the extreme weather events that are “exhibiting changes that may be related to climate change, but scientific understanding is not yet detailed enough to confidently project the direction and magnitude of future change.” The report also notes that “there is some indication that, in a warmer world, the number of days with conditions conducive to severe thunderstorm activity is likely to increase.”