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Live Updates: Southern States Face Another Assault by Dangerous Storms [1]
['Jin Yu Young', 'Emily Cochrane', 'Eliza Fawcett', 'Claire Fahy', 'The New York Times', 'Sarah Kramer Ozbun', 'Rory Doyle', 'Emma Bubola', 'Cassandra Vinograd']
Date: 2023-03-26
Damage to a neighborhood in Round Rock, Texas, after tornadoes ripped through in March 2022.
Scientists have been able to draw links between a warming planet and hurricanes, heat waves and droughts, attributing the likelihood that climate change played a role in individual isolated events. The same can’t be said for tornadoes yet.
Even as scientists are discovering trends around tornadoes and their behavior, it remains unclear the role that climate change plays. “For a lot of our questions about climate change and tornadoes, the answer is we don’t know,” said Harold Brooks, a senior research scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “We don’t see evidence for changes in average annual occurrence or intensity over the last 40 to 60 years.”
What causes a tornado?
Tornadoes form inside large rotating thunderstorms and the ingredients have to be just right. Tornadoes occur when there is a perfect mix of temperature, moisture profile and wind profile.
When the air is unstable, cold air is pushed over warmer humid air, creating an updraft as the warm air rises. When a wind’s speed or direction changes over a short distance, the air inside the clouds can start to spin. If the air column begins spinning vertically and rotates near the ground, it can intensify the friction on Earth’s surface, accelerating the air inward, forming a tornado.
How are they measured?
Like hurricanes and earthquakes, tornadoes are rated on a scale. The Enhanced Fujita, or EF, scale runs from 0 to 5.
Because it’s challenging to measure the winds in a tornado directly, surveyors usually evaluate tornadoes by their level of damage to different structures.
For instance, they may look to see if the damage is limited to missing roof shingles or whether entire sections of roofs or walls are missing. Based on the level of damage, scientists then reverse-engineer the wind speeds and assign a tornado a rating on the scale.
Have tornadoes changed over the years?
Researchers say that in recent years tornadoes seem to be occurring in greater “clusters,” and that the region known as tornado alley in the Great Plains, where most tornadoes occur, appears to be shifting eastward. The overall number of tornadoes annually is holding steady around 1,200.
In December 2021, a burst of deadly tornado activity across central and southern states came at a highly unusual time for the United States. March, with its warmer weather, is typically when tornado activity starts to increase.
Is climate change the cause?
The ingredients that give rise to tornadoes include warm, moist air at ground level; cool dry air higher up; and wind shear, which is the change in wind speed or direction. Each of these factors may be affected differently by climate change.
As the planet warms and the climate changes, “we don’t think they are all going to go in the same direction,” said Dr. Brooks of NOAA. For instance, overall temperature and humidity, which provide energy in the air, may rise with a warming climate, but wind shear may not.
“If there is not enough shear to make something rotate, it doesn’t matter how strong the energy is.” he said. “If there is all kind of wind shear, but you don’t have a storm, you won’t get a tornado, either.”
Although we know that climate change may be playing a role in making some storms more powerful, the complexity of tornadoes means that it is hard to extend that connection with certainty, especially for an individual event.
Scale is everything
A tornado’s relatively small size also makes it harder to model, the primary tool that scientists use when attributing extreme weather events to climate change. “We are working at such small scales that the model you would use to do the attribution studies just can’t capture the phenomenon,” Dr. Brooks said.
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[1] Url:
https://www.nytimes.com/live/2023/03/26/us/tornado-mississippi
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