The beginning of December marks the end of the 2020 hurricane season, which was by all measures unprecedented. It broke all of the records: most named storms, most storms to make landfall in Louisiana, strongest storm to hit Louisiana in 150 years, most storms to form in a single month. The list goes on and on.
For those of us living on the coast, it ranged from merely anxiety-inducing for some to totally devastating for others. But what can we learn from it? Is this climate change? Is this the new normal?
The answer, as is so often the case with science, is yes and no. There are a number of reasons for the hyperactive season — some climate-related, some human-related, some random. We got answers from some of the top hurricane scientists.
Warmer Gulf: climate change
Warm waters were the main cause of this unprecedented hurricane season. When temperatures rise in the air, it warms the water. The Gulf was exceptionally warm this year. It made the storms stronger and the season longer, caused more storms to form, and made them intensify more quickly.
“It's very likely that there's a human fingerprint on that warming,” said Jim Kossin, an atmospheric research scientist at the National Oceanic and Atmospheric Administration (NOAA.)
Changing wind patterns: climate change
Changes in the jetstream and other atmospheric changes are causing hurricanes to stall out longer and move more slowly. This can cause big storms to hover for a long time and dump a lot of rain, as was the case with Hurricane Sally. It can also cause them to veer all over the place and make landfall a bunch of times, like Hurricane Eta.
La Nina: not climate change
Scientists say this cyclical ocean-atmospheric phenomenon is partly why there were so MANY storms this year. The effect is marked by cooler-than-average sea surface temperatures across the central and eastern Pacific Ocean near the equator. This effect weakened the wind shear over the Caribbean Sea and tropical Atlantic Basin, enabling storms to develop and intensify.
More moisture: climate change
The warmer the air is, the more water vapor it holds, so the amount of rain that storms are dropping is higher. Scientists say the rate of rainfall is also increasing — that’s the amount a storm can drop over a period of time.
“Hurricanes and tropical cyclones globally have indeed changed over the past four decades, and the changes definitely have not been good,” Kossin said.
Scientists have found that while climate change is not expected to cause more storms, it is likely to make them more intense. That’s largely due to the increased moisture and increased heat.
Research is ongoing
Storms are also speeding up more right before they make landfall like we saw with Hurricane Zeta, which quickly lept from a Category 2 to nearly Category 3 within 24 hours. This happens when the storm gathers strength quickly as it moves over warm ocean waters.
“Storms intensify all the time,” said Phil Klotzbach, a research scientist at Colorado State University's Department of Atmospheric Science, which issues annual hurricane season forecasts. “That's not that unusual, but these storms this year rapidly intensified right up to the point of landfall.”
He said that creates a challenge for forecasters and for officials on the ground who are trying to coordinate evacuations and mitigate damage.
Kossin said scientists have observed decades-long periods of increased hurricane activity in the past, like in the ‘40s and ‘50s in the Atlantic. But since then, more people have moved to coastal areas, meaning storms are now causing way more damage.
Damage from hurricanes and tropical storms this year is estimated to be between $35 billion and $40 billion.
Weirdly, pollution actually decreases storms. The more pollution there is in the air, the more smoggy it is, the less sunlight reaches the ocean water and warms it up.
That’s why, in areas where pollution has dropped significantly in past decades, such as in the North Atlantic, storms have decreased. Some geoengineers are proposing methods of carpeting the air above the ocean to reduce the heat from the sun.
Ultimately, “there's a lot of randomness to it all,” Kossin said. “Even if we were to go carbon neutral tomorrow, these patterns are still going to have quite a lot of inertia and momentum going into the future.”
Support for the Coastal Desk comes from the Greater New Orleans Foundation, the Walton Family Foundation, and local listeners.