National Geographic News
A storm crosses Highway 50 in the Nevada desert.

A storm crosses Highway 50 in the Nevada desert.

Photograph by Jon Hicks, Corbis

Ker Than

for National Geographic

Published September 24, 2013

Continued global warming could help create atmospheric conditions that are fertile breeding grounds for severe thunderstorms and tornadoes in the United States, a new study suggests.

The findings, detailed in this week's issue of the journal of the Proceedings of the National Academy of Sciences, are based on the most comprehensive computer modeling work done to date of the two main atmospheric ingredients that scientists think contribute to thunderstorm formation.

One of those ingredients is known as the convective available potential energy, or CAPE, that is created as air in the lower atmosphere warms. The warm air rises, whisking moisture to higher altitudes.

The second ingredient is vertical wind shear, which is essentially the change in wind speed with height.

What's New?

For a severe thunderstorm to arise, CAPE must interact with strong vertical wind shear. But earlier studies concluded that while global warming will increase CAPE, it will decrease wind shear. Thus, the two ingredients were thought to cancel each other out.

But the new computer simulations by climate scientists Noah S. Diffenbaugh and Martin Scherer of Stanford University and Robert J. Trapp of Purdue University revealed a pattern that was missed in previous modeling work.

"What we've found is that the reduction in shear actually falls on days when there's low CAPE," explained Diffenbaugh.

In other words, when CAPE is high, vertical wind shear is more likely to be high as well, which means the total frequency of occurrence of severe thunderstorm environments actually increases as a result of global warming.

Diffenbaugh says his team would not have made their discovery had they not been able to access and run multiple climate models that were previously scattered across different scientific groups around the world.

"We had ten global climate data models running exactly the same experiment ... and they show high agreement on the results," Diffenbaugh said.

Why Is It Important?

The simulations all agreed that continued global warming will lead to increases in storm days over large areas of the eastern United States in the spring, winter, and autumn.

The changes mean that for springtime alone, severe thunderstorms could increase by as much as 40 percent over the eastern U.S. by the end of the century, Diffenbaugh said.

What Does This Mean?

Severe thunderstorms, which are often associated with heavy rainfall, hail, and even tornadoes, are one of the primary causes of major economic losses in the United States.

In 2012, seven of the country's $11 billion weather disasters were caused by severe thunderstorms and tornadoes.

"Sadly, we have many examples of cases where a single storm has had disastrous impact," Diffenbaugh said in a statement. "So a 25 or 30 percent increase in the annual occurrence represents a substantial increase in the overall risk."

What's Next?

Diffenbaugh stressed that this latest modeling work looks only at the likelihood that the atmospheric conditions that give rise to severe thunderstorms will form.

The models stop short of actually predicting whether these ripe atmospheric conditions will spawn severe thunderstorms or tornadoes. As a result, they cannot tell scientists whether future global warming–fueled storms will be more powerful or destructive than they are now.

The team hopes to create more sophisticated models that will be able to overcome this limitation. "What we need to do next is develop ways to better represent the processes that produce individual storms in the real atmosphere," Diffenbaugh said in statement.

Follow Ker Than on Twitter.

Robert Carmack
Robert Carmack

March 2014 Tornado Drought May Set Record: ‘For the 2nd consecutive year, U.S. March tornado counts are among the lowest on record’

Olman Castro
Olman Castro

lo que no se advierte a  nivel mundial, o todavia no ha sido comprendido, es la probabilidad que se de que llegue un momento donde el calentamiento de la superficie terrestre sea tan elevado como para no permitir que germinen las semillas de  aquellas plantas que nos alimentan hoy, hortalizas, gramineas, verduras... esto no ha sido considerado con seriedad, como para establecer un limite a nivel mundial, de  que ya no se deban cortar mas arboles y al contrario se hagan campañas de conservacion de la flora para mantener el equilibrio global de las temperaturas  que son considerables como optimas para el cultivo y la produccion de los alimentos.  en Costa Rica, por ejemplo, para la siembra del cafe, siempre ha existido la sombra de un arbol llamado poro, y en los ultimos años este arbol se fue secando y desapareciendo, y nadie se explica el porque del fenomeno, pero, si lo relacionamos con calentamiento de la tierra, y que se trata de una variedad cuyas raices necesitan mucha humedad, podriamos estar concluyendo que esto es una voz de alerta. 

Michael Mcbride
Michael Mcbride


David Wheeler
David Wheeler

The earth is 4.6 billion years old -- we've been keeping accurate weather records for only a little over a hundred years... at least be honest about your convictions. Of, I forgot, progressives aren't capable of that -- they're cowards.

Donald Bloodworth
Donald Bloodworth

I'll be ready for the next scary headline/article based on the next government sponsored, university driven report, because I unbolted my trailer at the foundation, tied two telephone poles, one at each end as masts to hold my hemp sails and got me some inflatable dinghies then tied them all the way around my mobile home just to be ready for the next wind driven flood!

Osmand Charpentier
Osmand Charpentier

Yes, yes, yes. Identical for 100.000 years of the modern human brain, which, however, seems to have appeared only 1000 years ago, or 50 years? 

Unknown civilizations disappeared, and we do not know why,   but yes, it sounds reasonable to say that nothing happened. Known civilizations that disappeared, and we know why, but it still sounds more sensible to say that nothing happened. So, if our civilization is disappearing, or is destined to disappear, continue to sound sensible to say: nothing happens. 

Is it luck or bad luck: I mean, our brain is useless, or worse, we are not using it, or worse, do not want to use it for fear.

All current issues of concern have a common denominator: Energy Crisis. And there is good news: OCEANOGENIC POWER OF PANAMA (

Mary Waterton
Mary Waterton

If it's too hot, it's global warming.

If it's too cold, it's global warming.

If it rains too little, it's global warming.

If it rains too much, it's global warming.

Brian Loysen
Brian Loysen

Global Warming =  more severe weather.  Global Cooling = more sever weather.  As with the silly adage about a butterfly flapping it's wings, one portion of the world must needs undergo change.

History says we were have experience ice ages.  One very interesting theory about that is shifting poles...if I am correct...given our titled planet accumulates at the poles until it is too much and there is a pole shift because of the weight of ice on the polar caps.  On the same the ice melts and the weight disperses away from the poles, polar shift. 

I'm not denying Global Warming.....I believe to an extent that yes we have helped speed along a process that is cyclical in its nature anyways.  The thing I take to task is the solution.  Crippling our economy to make changes we believe may help doesn't change worldwide pollution.

And how do you force the world to change?  Global War?  A lot of you that don't want us in other people's business because of oil interests don't seem to realize the level of control America would have to exert to force global change.  

SO do we allow the EPA to run amok in our country when the problem is continually shifting to the pollution of other countries?  China is terrible...just go ahead and convince them to make changes.

Hence my main issue with the new religious like science worship...Climatology.  It's great to recognize the problem..but we have a hard time enforcing things like the use of chemical weapons DESPITE a clear treaty against it.  I would love to see a change but don't see it happening without us or a collation of countries attempting to control the entire world.

Lynwood Hines
Lynwood Hines

Agree that the tabloid-like misleading headline is a bad sign, demonstrating that the decline of journalistic integrity is creeping into even our most respected and venerable institutions.  It's just sad.

That said... the article itself is well written.  I especially like how it is structured.

Terry Conklin
Terry Conklin

National Geographic should do better than conflicting title and context. .."to Spawn More Severe U.S. Thunderstorms" is not the same as "could spawn..." since it COULD do something else as well, weather being the fickle thing it is.

Phillip Noe
Phillip Noe

And what of all the unknowns out there, the unexpected weather and climate events brought on by our activities?  Who knows what they are.  Maybe some will be good but it is clear that the ones we know about are almost all bad.  From decreased fresh water supplies, to higher sea levels, to more acidic oceans.  It's NOT a pretty picture.

Those of us that understand that business as usual is dangerous should do something about it.  Contact your members of Congress.  Insist they work harder to reduce global emission.  Apathy is acquiescence.  For the health and safety of our future generations, lets make the effort.

Robert Strahlendorf
Robert Strahlendorf

The title of this article does not match the body of the article. "Global Warming to Spawn More Severe U.S. Thunderstorms: Study" is the title, but the body of the article said the study stops short of saying this weather will occur. This is what the tabloids do. Is National Geographic becoming a hyped tabloid?

The study stopped short because they no there is no way they can write code to simulate the atmosphere in the future. Also, we have had warming occur since the Little Ice Age. Is there any empirical evidence in the spawning of more severe thunderstorms since then or in the past 100 years? Probably not since the study didn't mention empirical evidence. 

Will Stewart
Will Stewart

@Donald Bloodworth You may want to only rely on reports from corporations that have a vested interest in the subject areas they release PR statements on. Don't even think of questioning them...

Donald Bloodworth
Donald Bloodworth

You can have my lance and burro, I reset the sails, put in a new grist stone and moved into the last windmill I attacked...

John C.
John C.

@Phillip Noe 

The same computer models didn't predict the leveling of global warming over the past 17 years despite the steady increase in global C02. Before completely upending the world economy and jacking our utility bills sky high maybe the science needs to be a little more refined, say to the point of actually predicting and explaining things like a 17 year leveling in global warming.  

John Patt
John Patt

@John C. @Phillip Noe There has been an increase in global warming since the late 90's, but it has not been statistically significant. That is not the same thing as saying there has been no warming.

Alternative energy in some cases is less expensive than fossil fuels, and is becoming more economical all the time. So I don't agree that our utility costs are going to be jacked sky high by using greener technology.


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