A devastating Dust Bowl heat wave is now more than twice as likely, study says

The Great Plains Dust Bowl of the 1930s was arguably the most devastating ecological disaster in American history, turning prairies into deserts and whipping up killer dust storms. The catastrophe was partly manmade — driven by decades of land mismanagement — and fueled by brutal heat waves and years of relentless drought.

More than eight decades later, the summer of 1936 remains the hottest summer on record in the  U.S. However, new research finds that the heat waves that powered the Dust Bowl are now 2.5 times more likely to happen again in our modern climate due to another type of manmade crisis — climate change.

Even though it seemed like a natural disaster, the groundwork for much of the suffering caused by the Dust Bowl was laid by humans. 

Until the late 1800s the Great Plains were covered by endless acres of native grasslands, well attuned to the unique climate of the region. That had all changed by the turn of the 20th century, as a series of federal land acts enticed pioneers to move to the region and set up farms with the promise of free or cheap land. 

With cold winters, hot summers and a dry, windy climate, the area was considered marginal farmland. But with demand from a growing wheat and cattle market, farms quickly replaced deep-rooted grasslands, which normally helped to trap soil and moisture even during droughts. 

The decimation of native grasslands led to a significant loss of both soil moisture and the ability to keep soil  in place. It is estimated that three to four inches of topsoil was blown away during the 1930s. To make matters worse, some relatively inexperienced farmers engaged in deep plowing of virgin topsoils and enabled overgrazing. 

This absence of sound land management led to a feedback loop, where the lack of vegetation and moist soils meant the land no longer had the ability to cool itself through evaporation. So when natural climate fluctuations in the Atlantic and Pacific Oceans led to a streak of years with heat and drought in the Plains, the land not only had no buffer, but actually acted to amplify the disaster.  

The authors of the study found that even way back then, emissions had already started to influence the climate. "These extremes occurred during a period of multidecadal warming, with early twentieth century global-scale drought likely amplified by greenhouse gases," they write.

The 1936 heat wave was so extreme it is considered a once-in-100-year event, with 25% of all U.S. daily heat records set during that summer and half of such records set during the 1930s. Temperatures routinely topped 110 degrees Fahrenheit. 

The images below show the area covered by the 1936 heat wave, and from top to bottom: the number of days with extreme heat, the length of the longest heat wave stretch, and the hottest temperatures recorded. 

When the Dust Bowl hit, day turned into night as biblical dust storms buried parts of roads and buildings, especially in parts of Kansas, Oklahoma and Texas. On "Black Sunday" in the Oklahoma Panhandle — April 14, 1935 — Thelmas Bemount Campbell described her terror to author Amy Dee Stephens as a dust storm enveloped her home:

"We could see it rolling toward us at a terrific speed like a prairie fire. The wind was so strong that we heard later it had broken the wind gauges…When it hit, everything became very still and we were enveloped in this terrible blackness. We couldn't see our hand in front of our face. Some people thought they had been struck blind." 

As the dust storms became larger and more intense, children developed fatal "dust pneumonia" and business owners, already reeling from the Great Depression, were devastated, some driven to suicide and others forced to flee with their families in a mass exodus. In total, the Dust Bowl killed around 7,000 people and left 2 million homeless.

The heat, drought and dust storms also had a cascade effect on U.S. agriculture. Wheat production fell by 36% and maize production plummeted by 48% during the 1930s.

The Dust Bowl is an example of an environmental disaster clearly made worse by the unintended consequences of man. And the study concludes that climate change may soon bring about the next one: "It is likely that the 1930s records will be broken in the near-future even if there is action to mitigate emissions."

To arrive at their conclusion, the researchers ran thousands of computer model simulations of the 1930s heat waves, but with atmospheric greenhouse gas concentrations at today's levels.

The study used a novel climate model developed at the University of Oxford that does not run on supercomputers, but rather on the personal computers of volunteers from around the world. This technique suited their particular 1930s heat wave investigation because thousands of simulations could be conducted for each Dust Bowl year.

The simulations showed that as a result of rapidly increasing heat-trapping greenhouse gases, the 1-in-100-year 1936 heat wave is, at the very least, now more of a 1-in-40-year event for the Great Plains — meaning a heat wave of that magnitude is now more than twice as likely and could occur twice in the average person's lifetime.

Lead author of the study Dr. Tim Cowan, of the University of Southern Queensland in Australia, cautions that even this 40-year return period is likely an underestimate, and in the future extreme heat waves will occur even more often.

But given the rise in greenhouse gases over many decades, CBS News asked Cowan why we haven't already seen a return of Dust Bowl-like conditions in the Great Plains. Cowan explains that the answers lie in the modern-day watering of crops. "Groundwater is used quite extensively across the U.S., and we know, from previous research, that increased irrigation and agricultural intensification has led to cooler summer maximum temperatures," he said.

But Cowan's work suggests that our luck will eventually run out, either when natural conditions and manmade climate change conspire to overwhelm the cooling influence of irrigation or when groundwater is sufficiently depleted.

In the western Great Plains the majority of groundwater comes from one of the world's largest aquifers -- the Ogallala Aquifer, which runs from Nebraska to Texas. But in recent decades, water is being extracted much faster than it is being replenished. Well outputs in the central and southern parts of the aquifer are declining due to excessive pumping, and prolonged droughts have parched the area, bringing back Dust Bowl-style storms.

According to the federal government's 2018 National Climate Assessment, parts of the Ogallala Aquifer should be considered a nonrenewable resource. 

As a result, Cowan warns, "Dwindling water availability in regions of low groundwater recharge may mean that cooler summer conditions may switch to warmer temperatures in decades to come under the influence of rising greenhouse gas emissions."

If these Dust Bowl conditions do return, scientists say we should prepare for a shock to the food system. A recent study predicted that the U.S. would exhaust 94% of its wheat reserves in a four-year Dust Bowl-like event. This would lead to a 31% loss of global wheat stocks.

Besides the impacts on food systems, an April study from the University of Washington finds the expected increase in extreme heat will also be a health shock. The research warns of danger for agricultural pickers in the U.S., with unsafe work days more than doubling by 2050 and heat waves happening five times more often as the planet continues to warm.

The bottom line, Cowan says: "It is likely that there will be more extreme heat wave conditions in the central U.S. in the future, given the rise in greenhouse gases levels, so communities and governments need to be prepared for this eventuality."