Why Hurricanes Are Becoming More Dangerous

Why Hurricanes Are Becoming More Dangerous

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A record-setting hurricane season just ended. Explore what we know, think we know, and are just learning about how climate change is influencing the world’s most dangerous storms. By Brandon Miller, Drew Kann, Judson Jones, Renée Rigdon and Curt Merrill, CNN
Illustrations by Leanza Abucayan, CNN

Published December 3, 2020

Katrina. Maria. Andrew. Haiyan.

Hurricanes are the most violent storms on the planet. The names of the most damaging ones live on because of the devastation they left in their wake.

Known outside of North America as tropical cyclones or typhoons, hurricanes are essentially massive engines of wind and rain that are fueled by warm ocean water and air.

This heat energy is converted into lashing winds and driving rainfall that can bring devastating impacts when they hit cities, homes and infrastructure.

Over the last two-plus centuries, human activity — mainly the burning of fossil fuels – has added lots of heat to the oceans and air where these storms are spawned.

The 2020 Atlantic hurricane season was the most active on record, and many of the storms that slammed into the Gulf Coast, Central America and the Caribbean this year exhibited hallmark signs that they were supercharged by global warming.

In 1961, Hurricane Esther became the first storm to be recorded by a weather satellite.

NASA

Though global temperature data goes back over 150 years, hurricane records are actually very sparse prior to the 1970s, when satellites first began capturing images of all of the world’s oceans.

While scientists are still learning exactly how this added heat is changing hurricanes, research shows that the storms are becoming more destructive in some key ways.

Here’s what scientists are most confident is happening to hurricanes as a result of climate change, what they think might be occurring and the biggest questions about how these massive storms are changing that remain unanswered.

What scientists know for sure

Sea level rise is making storm surge more dangerous

Hurricanes are categorized by their wind speeds, but the most deadly and destructive threat posed by most hurricanes is the storm surge they can produce.

Storm surge is the rapid rise in ocean levels brought about by the powerful winds and low pressure in a hurricane.

When a storm’s winds blow onshore, they can send feet of water rushing inland at depths far greater than even the most extreme high tides.

And when storm surge strikes a developed coastline, the cost in both lives and property can be enormous.

With global sea levels projected to rise this century, the risk of storm surge penetrating further inland will increase.

2010

Storm surge

2010 floodplain

1880 floodplain

2050

2050 floodplain

2010

1880

2100

2100 floodplain

2050

2010

1880

Note: Local factors such as tides and coastal profile will influence the extent of the floodplain.

Source: Union of Concerned Scientists

With global sea levels projected to rise this century, the risk of storm surge penetrating further inland will increase.

2010

Storm surge

2010 floodplain

1880 floodplain

2050

2050 floodplain

2010

1880

2100

2100 floodplain

2050

2010

1880

Note: Local factors such as tides and coastal profile will influence the extent of the floodplain.

Source: Union of Concerned Scientists

With global sea levels projected to rise this century, the risk of storm surge penetrating further inland will increase.

2010

Storm surge

2010 floodplain

1880 floodplain

2050

Storm surge

2050 floodplain

2010

1880

2100

Storm surge

2100 floodplain

2050

2010

1880

Note: Local factors such as tides and coastal profile will influence the extent of the floodplain.

Source: Union of Concerned Scientists

With global sea levels projected to rise this century, the risk of storm surge penetrating further inland will increase.

2010

Storm surge

2010 floodplain

1880 floodplain

2050

Storm surge

2050 floodplain

2010

1880

2100

Storm surge

2100 floodplain

2050

2010

1880

Note: Local factors such as tides and coastal profile will influence the extent of the floodplain.

Source: Union of Concerned Scientists

While no tide gauge measurements were available in the hardest-hit parts of the Bahamas when Hurricane Dorian struck in 2019, witnesses reported that the storm put parts of the islands under as much as 20 feet of water.

During the height of Hurricane Dorian, Michael Pintard, Bahamas’ Minister of Agriculture, recorded this video from the second story of his house. Water is seen lapping against the windows, which he estimates in the video to be nearly 20 feet high.

Sea level rise of only a couple of inches can make a dramatic difference in how far inland storm surge can travel.

Already, storm surge has gotten worse because sea levels are rising – and fast.

“This is making the storms more dangerous as it leads to higher inundation levels,” said Tom Knutson, a meteorologist at the National Oceanic and Atmospheric Administration who leads the agency’s weather and climate dynamics division.

If humans continue to emit heat-trapping gases into the atmosphere, scientists expect that sea levels will climb even higher, putting major cities at an even greater risk.

Sea levels are now likely to rise more than 3 feet by 2100, according to the findings of a landmark report published last year by the UN’s Intergovernmental Panel on Climate Change.

Generally speaking, a rise in sea levels of 2 to 3 feet would mean that a Category 1 hurricane could be capable of inflicting the kind of storm surge damage we would expect today from a Category 2 storm.

In the Southeastern US alone, the annual cost of storm surge damage is projected to grow to $56 billion by 2050, according to the US government’s 2018 National Climate Assessment. And that’s even if global emissions of heat-trapping gases are moderately curbed in the next two decades.

Storms are getting wetter

While storm surge is responsible for about half of all fatalities in landfalling hurricanes, the heavy rainfall such storms produce can also be deadly. Since 1970, nearly 60% of the flood-related, non-storm-surge deaths from tropical storms have been caused by inland flooding.

The increase in hurricane rainfall can be explained by physics — specifically, the Clausius-Clapeyron equation, which holds that for each degree Celsius of warming, 7% more water vapor should be available in the atmosphere to potentially fall as rain.

“Simply put, warmer air holds more water vapor,” said Jim Kossin, an atmospheric research scientist at NOAA’s National Center for Environmental Information.

Baseline

+1 degree C

+2 degrees C

That would mean that in a world warmed by two degrees Celsius, you would have, on average, around 14% more water vapor in the atmosphere.

Computer models consistently show that hurricane rainfall is increasing already, as one would expect as the planet warms.

But because observation stations that monitor rainfall are sparse and hurricane satellite data only goes back a few decades, we can’t yet draw conclusions about how much climate change has affected rainfall, said Kossin.

However, there have been several recent storms that provide anecdotal evidence.

In 2017, Hurricane Harvey dumped the most rain ever recorded during any weather event in the US, with more than 40 inches falling during the storm’s four-day slog across Texas and Louisiana. Scientists estimated that Harvey’s incredible rainfall totals were made 15% more intense and three times more likely due to global warming.

Flood detection percentage*

25

50

75

100

Beaumont

LA.

Houston

TEXAS

Galveston

Victoria

Harvey’s path

*Data represent the number of times a pixel was identified as ‘flooded’ divided by the number of times the pixel was sampled.

Sources: NOAA (Harvey’s path); NASA MSFC SPoRT, Copernicus EMS, MDA Systems, ARIA NASA JPL/Caltech via GeoPlatform.gov (flood analysis)

Flood detection percentage*

25

50

75

100

Beaumont

LA.

Houston

TEXAS

Galveston

Victoria

Harvey’s path

*Data represent the number of times a pixel was identified as ‘flooded’ divided by the number of times the pixel was sampled.

Sources: NOAA (Harvey’s path); NASA MSFC SPoRT, Copernicus EMS, MDA Systems, ARIA NASA JPL/Caltech via GeoPlatform.gov (flood analysis)

Beaumont

LA.

Houston

TEXAS

Galveston

Victoria

Harvey’s path

Flood detection percentage*

25

50

75

100

*Data represent the number of times a pixel was identified as ‘flooded’ divided by the number of times the pixel was sampled.

Sources: NOAA (Harvey’s path); NASA MSFC SPoRT, Copernicus EMS, MDA Systems, ARIA NASA JPL/Caltech via GeoPlatform.gov (flood analysis)

Beaumont

LA.

Houston

TEXAS

Galveston

Victoria

Harvey’s path

Flood detection percentage*

25

50

75

100

*Data represent the number of times a pixel was identified as ‘flooded’ divided by the number of times the pixel was sampled.

Sources: NOAA (Harvey’s path); NASA MSFC SPoRT, Copernicus EMS, MDA Systems, ARIA NASA JPL/Caltech via GeoPlatform.gov (flood analysis)

Beaumont

LOUISIANA

Houston

TEXAS

Galveston

Victoria

Harvey’s path

Flood detection percentage*

25

50

75

100

*Data represent the number of times a pixel was identified as ‘flooded’ divided by the number of times the pixel was sampled.

Sources: NOAA (Harvey’s path); NASA MSFC SPoRT, Copernicus EMS, MDA Systems, ARIA NASA JPL/Caltech via GeoPlatform.gov (flood analysis)

The following year, Hurricane Florence swamped parts of North Carolina with nearly three feet of rain, shattering the state’s previous record for tropical storm rainfall.

What scientists think they know

Storms are getting stronger

This added heat is likely allowing hurricanes to pack even greater wind speeds.

Amount of heat in the upper layer of the ocean, compared to the average from 1955-2006. Data is for the top 700 meters (2300 feet) of the ocean and given in 10^22 Joules.

20

15

10

5

-5

-10

1960

’70

’80

’90

2000

’10

’20

Source: NOAA

Amount of heat in the upper layer of the ocean, compared to the average from 1955-2006. Data is for the top 700 meters (2300 feet) of the ocean and given in 10^22 Joules.

20

15

10

5

-5

-10

1960

’70

’80

’90

2000

’10

’20

Source: NOAA

Amount of heat in the upper layer of the ocean, compared to the average from 1955-2006. Data is for the top 700 meters (2300 feet) of the ocean and given in 10^22 Joules.

20

15

10

5

-5

-10

1960

1970

1980

1990

2000

2010

2020

Source: NOAA

Amount of heat in the upper layer of the ocean, compared to the average from 1955-2006. Data is for the top 700 meters (2300 feet) of the ocean and given in 10^22 Joules.

20

15

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