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Tornadoes and climate change: what we know and what we don’t know

This is an updated version of the story originally published on March 6, 2019.


1,000 or more tornado Peak months for twisters are typically April, May, and June, and occur nationwide.

climate change extreme weather conditions More frequent and more serious, current science is inconclusive about how much climate change will affect tornadoes.

However, climate change appears to be changing the concentration and extent of tornadoes, pushing them into more vulnerable areas. Moreover, evidence suggests that in a warmer future there will be a more favorable environment for severe weather and possibly tornadoes.

Recent tornado trends

Finding trends in tornado numbers and strength is complicated. This is because the U.S. tornado record is fairly short (since the 1950s) and compiled by eyewitness reports, which are prone to many uncertainties.

With more people now living in remote areas, more tornadoes are being observed, so it’s logical to assume that the number of tornadoes will increase. graph It looks flat.

To the naked eye, there appears to be a trend the following severe tornado. However, past discrepancies in determining tornado strength make records difficult to trust. there is evidence Tornadoes may have been rated as more powerful than they actually were before the Fujita scale was adopted in the late 1970s.

( Enhanced Fujita Scalewas adopted in 2007 and is currently used to rank the most severe EF-0 to EF-5 tornadoes based on estimated wind speed and associated damage. )

The bottom line is that so far we haven’t seen any major trends in the overall number or intensity of tornadoes. But that doesn’t tell the whole story.

The Science of Tornadoes in a Warming Climate

Powerful tornadoes form from a combination of warm, moist updrafts and strong “wind shear.” Wind shear is the change in wind speed and/or direction due to height, which helps provide spin to supercell thunderstorms that help form tornadoes.

In this warming world, global climate models clearly show increased warmth and humidity. However, climate models also suggest a general decrease in wind shear in the future. So which wins: an increase in warm, moist air or a modest decrease in shear?

the devil is in the details

Armed with the Global Climate Model Ensemble, a team of researchers at Stanford and Purdue Universities in 2013 found In response to global warming, there will be a “certain increase in the occurrence of severe thunderstorm conditions in the eastern United States.”

This result is not surprising given that warm, moist and unstable air increases the energy of thunderstorms.

But the team also discovered something unexpected. Computer models showed that as temperatures rise, low levels of windshear increase on days when the air is more volatile. The team said it suggested “the increasing likelihood of atmospheric conditions contributing to the most severe events, including tornadoes.”

It is worth noting that wind shear does indeed decrease in their study, but the decrease is concentrated on more stable, less stormy days. Therefore, a general reduction in wind shear does not affect tornadoes.

Extreme tornado outbreaks become even more extreme

more recent study A paper published in 2016 titled “More Tornadoes in the Most Extreme U.S. Tornado Occurrences” suggests that some of the conclusions of the 2013 study may be happening now. increase.

CBS News spoke to the lead author of the 2016 study, Columbia University. Professor Michael K. Tippett“Extreme weather conditions associated with severe thunderstorms show a consistent upward trend,” he explained.


Study finds climate change may be intensifying tornadoes

05:07

Tippett analyzed the tornado record going back to the 1950s and found that “the frequency of occurrences in the United States with many tornadoes is increasing, and the more extreme occurrences are increasing faster.”

But Tippett said it’s unclear whether the increase in tornadoes with each outbreak is driven by climate change. The changes are not necessarily of the kind expected from climate change.

Specifically, the study found that on days with tornadoes, unstable air did not increase as climate change implies. Instead, it is the wind shear that is increasing.

“Either we don’t understand the full impact of climate change, or it’s not climate change,” Tippett said.

However, in the future, he warned, “it is clear that climate change will have consequences, such as more frequent favorable conditions for supercell thunderstorms and a northward expansion of favorable regions.” bottom.

“Tornado Yokocho” shifts to the east

A fall 2018 study concluded that it is likely to be the most impactful of all tornado trends. “Tornado Alley” spreads to the east From the Plains States towards the weaker and more densely populated Southeast. The study found that the southeastern region has more trees and more fragile homes that put residents at risk, so the chances of disasters could triple he. This shift is occurring as drier, more stable air from the southwest desert pushes the thunderstorm layer eastward.

Lead author Victor Gencini told CBS News: “It is safe to say that climate change is causing this eastward shift. Hypotheses and computer simulations confirm what we are observing and predicting in the future. ”



Summarize this content to 100 words

This is an updated version of the story originally published on March 6, 2019.1,000 or more tornado Peak months for twisters are typically April, May, and June, and occur nationwide. climate change extreme weather conditions More frequent and more serious, current science is inconclusive about how much climate change will affect tornadoes.

However, climate change appears to be changing the concentration and extent of tornadoes, pushing them into more vulnerable areas. Moreover, evidence suggests that in a warmer future there will be a more favorable environment for severe weather and possibly tornadoes.Recent tornado trendsFinding trends in tornado numbers and strength is complicated. This is because the U.S. tornado record is fairly short (since the 1950s) and compiled by eyewitness reports, which are prone to many uncertainties.

With more people now living in remote areas, more tornadoes are being observed, so it’s logical to assume that the number of tornadoes will increase. graph It looks flat.To the naked eye, there appears to be a trend the following severe tornado. However, past discrepancies in determining tornado strength make records difficult to trust. there is evidence Tornadoes may have been rated as more powerful than they actually were before the Fujita scale was adopted in the late 1970s.( Enhanced Fujita Scalewas adopted in 2007 and is currently used to rank the most severe EF-0 to EF-5 tornadoes based on estimated wind speed and associated damage. ) The bottom line is that so far we haven’t seen any major trends in the overall number or intensity of tornadoes. But that doesn’t tell the whole story.

The Science of Tornadoes in a Warming ClimatePowerful tornadoes form from a combination of warm, moist updrafts and strong “wind shear.” Wind shear is the change in wind speed and/or direction due to height, which helps provide spin to supercell thunderstorms that help form tornadoes.
Tornadoes form when certain factors are in place, including high instability and vertical wind shear, which means the wind changes with altitude. This slide explains the science of tornado formation and also provides safety tips. #SpringSafety #houwx #bcswx pic.twitter.com/MGRKquOIKm— NWS Houston (@NWSHouston) March 8, 2018

In this warming world, global climate models clearly show increased warmth and humidity. However, climate models also suggest a general decrease in wind shear in the future. So which wins: an increase in warm, moist air or a modest decrease in shear?the devil is in the detailsArmed with the Global Climate Model Ensemble, a team of researchers at Stanford and Purdue Universities in 2013 found In response to global warming, there will be a “certain increase in the occurrence of severe thunderstorm conditions in the eastern United States.”This result is not surprising given that warm, moist and unstable air increases the energy of thunderstorms.But the team also discovered something unexpected. Computer models showed that as temperatures rise, low levels of windshear increase on days when the air is more volatile. The team said it suggested “the increasing likelihood of atmospheric conditions contributing to the most severe events, including tornadoes.”It is worth noting that wind shear does indeed decrease in their study, but the decrease is concentrated on more stable, less stormy days. Therefore, a general reduction in wind shear does not affect tornadoes.Extreme tornado outbreaks become even more extrememore recent study A paper published in 2016 titled “More Tornadoes in the Most Extreme U.S. Tornado Occurrences” suggests that some of the conclusions of the 2013 study may be happening now. increase.

CBS News spoke to the lead author of the 2016 study, Columbia University. Professor Michael K. Tippett”Extreme weather conditions associated with severe thunderstorms show a consistent upward trend,” he explained.

Study finds climate change may be intensifying tornadoes

05:07

Tippett analyzed the tornado record going back to the 1950s and found that “the frequency of occurrences in the United States with many tornadoes is increasing, and the more extreme occurrences are increasing faster.”But Tippett said it’s unclear whether the increase in tornadoes with each outbreak is driven by climate change. The changes are not necessarily of the kind expected from climate change.Specifically, the study found that on days with tornadoes, unstable air did not increase as climate change implies. Instead, it is the wind shear that is increasing. “Either we don’t understand the full impact of climate change, or it’s not climate change,” Tippett said.However, in the future, he warned, “it is clear that climate change will have consequences, such as more frequent favorable conditions for supercell thunderstorms and a northward expansion of favorable regions.” bottom.”Tornado Yokocho” shifts to the eastA fall 2018 study concluded that it is likely to be the most impactful of all tornado trends. “Tornado Alley” spreads to the east From the Plains States towards the weaker and more densely populated Southeast. The study found that the southeastern region has more trees and more fragile homes that put residents at risk, so the chances of disasters could triple he. This shift is occurring as drier, more stable air from the southwest desert pushes the thunderstorm layer eastward.

Lead author Victor Gencini told CBS News: “It is safe to say that climate change is causing this eastward shift. Hypotheses and computer simulations confirm what we are observing and predicting in the future. ”

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Jeff Veradelli

Jeff Berardelli is a meteorologist and climate expert for CBS News.

https://www.cbsnews.com/news/tornadoes-climate-change-what-we-know/ Tornadoes and climate change: what we know and what we don’t know

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