July 5, 2022

Hurricane Ida intensified overnight and became a Category 4 storm in a matter of hours. The rapid increase in strength begs the question of how much climate change will affect hurricanes in the Atlantic. While researchers cannot say for sure whether human-caused climate change will mean longer or more active hurricane seasons in the future, there is broad consensus: global warming is changing storms.

Scientists say the Atlantic’s unusually warm surface temperatures helped increase storm activity. “It is very likely that human-made climate change contributed to this unusually warm ocean,” said James P. Kossin, a climate scientist with the National Oceanic and Atmospheric Administration. “Climate change makes hurricanes more likely to behave in certain ways.”

Here are some of those options.

There is solid scientific consensus that hurricanes are getting stronger.

Hurricanes are complex, but one of the key factors that will determine how severe a particular storm will ultimately be is sea surface temperature, as warmer water provides more energy that powers storms.

“The potential intensity is increasing,” says Kerry Emanuel, professor of atmospheric science at the Massachusetts Institute of Technology. “We predicted 30 years ago that it would go up, and observations show that it will go up.”

Stronger winds mean broken power lines, damaged roofs and, in conjunction with rising sea levels, worse coastal flooding.

“Even if the storms themselves did not change, the storm surge rides at elevated sea levels,” said Dr. Emanuel. As an example, he cited New York City, where sea levels have risen by about a foot in the last century. “If Sandy’s flood had happened in 1912 instead of 2012,” he said, “it probably wouldn’t have flooded Lower Manhattan.”

The warming also increases the amount of water vapor that the atmosphere can hold. In fact, every degree Celsius of warming causes the air to absorb around 7 percent more water.

This means that we can expect higher amounts of precipitation in future storms.

The researchers do not yet know why storms move more slowly, but they are. Some say that slowing global atmospheric circulation or global winds may be partly responsible.

In a 2018 paper, Dr. Kossin notes that hurricanes over the United States have slowed 17 percent since 1947. Combined with the increase in rainfall rates, storms are causing a 25 percent increase in local rainfall in the United States, he said.

Slower, wetter storms also make flooding worse. Dr. Kossin compared the problem to walking around your yard while spraying water on the ground with a hose. If you walk fast, the water has no chance of pooling. But if you go slowly, he said, “you will get a lot of rain under you”.

As warmer water helps heat hurricanes, climate change increases the area in which hurricanes can form.

There is a “migration of tropical cyclones out of the tropics and towards subtropics and mid-latitudes,” said Dr. Kossin. That could mean more storms hit land at higher latitudes, like the United States or Japan.

With the warming of the climate, the researchers also expect that the storms will intensify faster. Researchers still aren’t sure why this is happening, but the trend seems clear.

In a 2017 paper based on climate and hurricane models, Dr. Emanuel states that storms that intensify rapidly – those that increase their wind speed by 70 miles per hour or more in the 24 hours prior to landfall – were rare in the period from 1976 to 2005. On average, he estimated, their probability was in these years about once a century.

He found that by the end of the 21st century, these storms could form every five or ten years.

“This is every meteorologist’s nightmare,” said Dr. Emanuel. When a tropical storm or Category 1 hurricane evolves into a Category 4 hurricane overnight, he said, “there is no time to evacuate people.”