FACT CHECK: Are Tropical Storms Getting ‘Bigger, Larger, More Violent’?

David Sivak | Fact Check Editor

National Guard Bureau Chief Joseph Lengyel said Tuesday that he believes storms are becoming “bigger, larger, more violent” due to climate change.

“I do think that the climate is changing, and I do think that it is becoming more severe,” said Lengyel. “I do think that storms are becoming bigger, larger, more violent.”

The Daily Caller News Foundation investigated whether tropical cyclones have indeed become more intense over time.

Verdict: Unsubstantiated

Although a higher frequency of powerful Atlantic storms has been recorded in recent decades, it’s unclear whether this is a long-term trend, or merely the result of natural variability and an incomplete historical record. Certain meteorologists predict there will be more intense storms in the 21st century, but some forecasting models show no significant increase.

Fact Check:

Since the 2017 hurricane season began, Hurricane Harvey caused catastrophic flooding in Texas, Hurricane Irma became one of the strongest Atlantic storms on record and four of the seven hurricanes formed this year have reached Category 3 winds or higher.

According to the National Oceanic and Atmospheric Administration (NOAA), Atlantic storms have, in fact, become more active in recent years. But Gerry Bell, lead seasonal hurricane forecaster for NOAA, attributes the intensity of storms to a natural cycle called Atlantic Multidecadal Oscillation (AMO).

“The main reason is this AMO pattern rather than some kind of long, upward trend,” Bell told TheDCNF.

The Atlantic basin undergoes alternating periods of higher and lower cyclone activity in which the frequency, intensity and duration of tropical storms track together.

“When you have the set of conditions that produce more active seasons – warmer ocean waters, more conducive winds coming off of Africa, an extensive area of weaker wind sheer – that combination of conditions produces more storms, stronger storms and longer-lasting storms,” Bell told TheDCNF.

A cycle of stronger activity began in 1995, but severe storms are nothing new. In fact, some of the most intense storms ever recorded formed in the 1800s.

Tropical storm activity may be in a short-term upswing, but meteorologists cannot identify a statistically significant change in activity over a longer span of time. “When adjusted with an estimate of storms that stayed at sea and were likely ‘missed’ in the pre-satellite era, there is no significant increase in Atlantic hurricanes since the late 1800s,” concluded a review by NOAA.

There is evidence, however, that the frequency of powerful Category 4 and 5 hurricanes may have increased since the 1940s, although NOAA cautions that a reliable trend cannot yet be established from the data.

While it’s unclear whether the higher frequency should be attributed to a long-term trend or simply natural variability, meteorologists have reason to believe that climate change may lead to stronger storms in the 21st century.

“Future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100,” read a 2010 review by the World Meteorological Organization. NOAA arrived at a similar conclusion and predicts a 30 percent increase in the damage caused by storms in the Atlantic basin.

Interestingly, these forecasts show the frequency of hurricanes decreasing even as their intensity increases. In climate change models, warmer sea surface temperatures produce stronger storms, but warming of the atmosphere and greater vertical wind sheer dampens their intensity.

Not all models predict the increased severity of Atlantic storms, and NOAA advises that there is no consensus among studies on what the frequency, intensity and duration of hurricanes will be for the remainder of the 21st century.

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David Sivak

Fact Check Editor

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