Global warming is likely to increase severe thunderstorm conditions in US, researchers find

Sep 23, 2013

In 2012, 11 weather disasters in the United States crossed the billion-dollar threshold in economic losses. Seven of those events were related to severe thunderstorms. New climate analyses led by Stanford scientists indicate that global warming is likely to cause a robust increase in the conditions that produce these types of storms across much of the country over the next century.

Severe thunderstorms are one of the primary causes of catastrophic losses in the United States and often exhibit the conditions that generate heavy rainfall, damaging winds, hail and tornadoes.

Sparse historical data describing the atmospheric conditions that cause severe thunderstorms has limited scientists' ability to project the long-term on storm frequency. But, using a complex ensemble of physics-based , researchers led by Noah Diffenbaugh, an associate professor of environmental Earth system science at Stanford, have produced the most comprehensive projections of severe storm conditions for the next century.

Scientists have identified two main ingredients involved in generating a severe thunderstorm. The first is that the atmosphere must contain a significant amount of what scientists call convective available potential energy (CAPE), created as the air in the low atmosphere warms. The warm air rises, carrying with it moisture to higher altitudes.

To transform into a severe thunderstorm, CAPE must also interact with strong – essentially a moving wind current that organizes the atmospheric energy and moisture such that it can sustain a storm.

Climate researchers have previously hypothesized that global warming will increase CAPE and cause an overall decrease in wind shear, which created uncertainty about the net effect.

The new climate model experiment that Diffenbaugh and his co-authors analyzed, called the Coupled Model Intercomparison Project (CMIP5), confirms these competing effects, but in a different way than previously believed.

Although the climate model experiment does indicate an overall decrease in the average amount of wind shear, the researchers found that the bulk of that decrease occurs on days that produce levels of CAPE that are much lower than is normally seen during severe storms.

The net effect is that the increases in CAPE on other days drive increases in the occurrence of severe thunderstorm environments.

"We're seeing that global warming produces more days with high CAPE and sufficient shear to form severe thunderstorms," said Diffenbaugh, who is also a senior fellow at the Stanford Woods Institute for the Environment.

Stormy springs ahead

The analysis carved the United States into boxes that were roughly 60 miles on a side and assessed the climate conditions that could emerge over the next century. The analysis showed the biggest changes occurring in the spring season, with each box in the central United States experiencing about two-and-a-half additional storm days per spring by the late 21st century.

The researchers also reported that sustained global warming is likely to cause robust increases in storm days over large areas of the eastern United States not only in spring but also in winter and autumn. While the summer season also showed increases over the region as a whole, those increases were the least robust within the region and across the different climate models.

An additional few days of severe storm conditions might not seem like a large change, but Diffenbaugh emphasized that the projected increases are in fact substantial compared to the frequency of occurrence in the current climate.

"We are looking at the conditions that produce severe events, which are relatively rare at present," Diffenbaugh said. "For example, the changes during spring represent an increase of about 40 percent over the eastern U.S. by the late 21st century."

Diffenbaugh also emphasized even a single severe storm can cause very high levels of damage.

"The severe thunderstorms we experience now can result in very high ," Diffenbaugh said. "Sadly, we have many examples of cases where a single storm has had disastrous impact. So a 25 or 30 percent increase in the annual occurrence represents a substantial increase in the overall risk."

Potential for more tornadoes

Such storms also create conditions that can lead to tornado formation, although the researchers stress caution in drawing conclusions specifically about the effect of global warming on tornadoes.

"We have tried to analyze the atmospheric conditions that are associated with tornadoes," Diffenbaugh said. "Although we do see that those conditions increase in occurrence in response to , it is important to bear in mind that we are not resolving tornadoes in these experiments."

Diffenbaugh hopes to build on this research to improve the understanding of the atmospheric dynamics that lead to the development of severe thunderstorms, and to better incorporate those processes into climate models.

The study is published in the current issue of Proceedings of the National Academy of Sciences.

"These are rare but significant events," Diffenbaugh said. "This new set of global climate model experiments has provided some important new insights. What we need to do next is develop ways to better represent the processes that produce individual storms in the real atmosphere."

Explore further: Global warming has increased risk of record heat, scientists say

More information: Robust increases in severe thunderstorm environments in response to greenhouse forcing, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1307758110

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User comments : 12

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Tom_Andersen
2.2 / 5 (23) Sep 23, 2013
Yet tornadoes are not increasing in number.
http://wattsupwit...ime-low/
Neinsense99
2.5 / 5 (24) Sep 23, 2013
Yet tornadoes are not increasing in number.
http://wattsupwit...ime-low/

Number is not equal to severity.
Your source site is a known denialist cesspool with no scientific credibility.
discouragedinMI
1.9 / 5 (22) Sep 23, 2013
Yet tornadoes are not increasing in number.
http://wattsupwit...ime-low/

Number is not equal to severity.
Your source site is a known denialist cesspool with no scientific credibility.


Then number of severe tornades and hurricanes is down in the last several decades.
ubavontuba
1.9 / 5 (23) Sep 23, 2013
Global warming is likely to increase severe thunderstorm conditions in US, researchers find
But then when it doesn't, alarmist scientists will find some way to blame it on global warming!
NikFromNYC
2 / 5 (24) Sep 23, 2013
Neinsense knows, like anybody familiar with skeptical arguments knows, that hurricanes have petered out in the last decade, and he already *knows* that this includes severity too.

The skeptical blog post link contains a carbon copy of an official NOAA yearly summary that points out this contemporary loss of weather intensity.

This is how activist Climatology cult bubbles maintain themselves: members compete to create the most strident public displays of dedication to bullshit, projecting their own creepy activist huddling in natural climate change denial insider forums, always group bonding, saving the world from critical reason, saving themselves from individual responsibility to stand up and state the real facts of the case. Only petrodollar king Al Gore has scientific credibility!
mrmortgage
2.1 / 5 (23) Sep 23, 2013
This so called study is sheer nonsense and just wishful thinking because there has been no significant surface warming in over 15 years.
The Sun is going to rise tomorrow not "is likely to rise" .
I am sick and tired of these so called scientists using this "is likely" phrase and really saying nothing of value.
NikFromNYC
2 / 5 (22) Sep 23, 2013
Those who call theoretical computer model runs devoid of comparison with actual trends "experiments" are exactly those with "no scientific credibility" and their emergency funding status is now collapsing.

"This new set of global climate model experiments has provided some important new insights."

Yet it is precisely due to the hurricane drop off in our naturally warm era that the odd bogeyman of mere thunderstorms must now support climate alarm. No longer are crops saved either, just gloom and doom t-h-u-n-d-e-r-s-t-o-r-m damage reports. Next will be killer bees. Oh, they tried that scare already, those who tried to claim scientific credibility simply for being academics.
jyro
2.1 / 5 (21) Sep 23, 2013
Every weather, climate, hurricane, global warming model has been proven to be wrong.
Water_Prophet
1 / 5 (17) Sep 23, 2013
The Water predicts more but less intense storms.
ekim
1.3 / 5 (8) Sep 24, 2013
The Green Economy is coming. This is evident by the distance to your nearest electric vehicle charging station. Your belief or non-belief in global warming is irrelevant. Money and investment dictates the future.
freethinking
1.7 / 5 (22) Sep 24, 2013
Problem is is hurricanes increase in frequency it's AGW. If hurricanes decrease in frequency it's AGW. If hurricanes intensity increases it's AGW. If hurricanes intensity decreases it's AGW. If it rains more than usual it's AGw. If it rains less than usual it's AGW. If it snows .... etc....

If Al Gore makes more money it's AGW.
If Progressive Government gives money to it's favored sectors (who for some strange reason then give a lot of donations to their re-election campaigns) it's AGW
If Progressives can use an argument to control people, it's AGW
ekim
1.2 / 5 (9) Sep 24, 2013
People give Al Gore money to speak. This is an perfect example of capitalism. A successful idea being marketed to the masses for profit. How much money do you receive for your ideas?