What a warmer world means for hurricanes

When Hurricane Ian hit Florida, was one of the strongest United States hurricanes on record, and followed a two-week series of massive, destructive storms around the world.

A few days earlier in the Philippines, Typhoon Noru gave new meaning to rapid intensity when it exploded from a tropical storm with 50 mph winds to a Category 5 monster with 155 mph winds the next day. Hurricane Fiona flooded Puerto Rico and subsequently became Canada’s most intense storm on record. Hurricane Merbok swept across the warm Pacific Ocean and destroyed more than 1,000 miles of Alaska’s coastline.

Major storms hit from the Philippines in the western Pacific to the Canary Islands in the eastern Atlantic, Japan and Florida in the mid-latitudes, and western Alaska and the Canadian Maritimes in the high latitudes.

Many people ask about the role that global warming plays in storms like these. It’s not always a simple answer.

It is clear that climate change is increasing peak hurricane intensity and rainfall rate and that it is also increasing mean sea level and thus storm surge. The effect on the total number of hurricanes is currently uncertain, as are other aspects. But as hurricanes emerge, we expect more of them to be major storms. Hurricane Ian and other recent storms, including the 2020 Atlantic season, provide a glimpse of what that might look like.

Our research has focused on hurricanes, climate change and the water cycle for years. Here’s what scientists know so far.

Precipitation: Temperature has a clear effect

The temperature of both the ocean and the atmosphere is critical to hurricane development.

Hurricanes are fueled by the release of heat when water evaporating from the ocean’s surface condenses into the storm’s rain.

A warmer ocean produces more evaporation, which means there is more water in the atmosphere. A warmer atmosphere can hold more water, which allows for more rain. More rain means more heat is released, and more heat means stronger winds.

These are basic physical properties of the climate system, and this simplicity lends great confidence to scientists’ expectations of storm conditions as the planet warms. The potential for greater evaporation and higher precipitation rates generally applies to all types of storms, on land or at sea.

This basic physical understanding confirmed in computer simulations of these storms in current and future climates, as well as recent events, leads to high confidence that hurricane rainfall rates are increasing by at least 7 percent per degree of warming.

Storm force and rapid intensification

Scientists also have high confidence that wind speeds will increase in a warming climate and that the percentage of storms that intensify into strong Category 4 or 5 storms will increase. Similar to precipitation rates, increases in intensity are based on the physics of extreme precipitation.

Damage is exponentially related to wind speed, so more intense storms can have a greater impact on lives and economies. The damage potential from a Category 4 storm with 150 mph winds like Ian made landfall is about 256 times that of a Category 1 storm with 75 mph winds.

Whether warming causes storms to intensify faster is an active area of ​​research, with some models offering evidence that this is likely to happen. One of the challenges is that the world has limited reliable historical data to identify long-term trends. Atlantic hurricane observations date back to the 1800s, but have only been considered globally reliable since the 1980s, with satellite coverage.

That said, there is already some evidence that an increase in rapid intensification is discernible in the Atlantic.

During the last two weeks of September 2022, both Noru and Ian experienced rapid intensification. In Ian’s case, successful rapid intensification forecasts were issued several days earlier when the storm was still a tropical depression. They demonstrate the significant progress in intensity predictions in recent years, although the improvements are not uniform.

There is some evidence that, on average, the location where storms reach their maximum intensity is moving poleward. This would have significant implications for the location of the storm’s main impacts. However, it is not yet clear that this trend will continue in the future.

Storm: Two major influences

Storm surge—the rise of water on a coast caused by a storm—is related to several factors, including storm speed, storm size, wind direction, and coastal seafloor topography. Climate change could have at least two major impacts.

Stronger storms increase the chance of higher waves, and rising temperatures cause sea levels to rise, which increases the height of the water, so the storm surge is now higher than before relative to land. As a result, there is high confidence for an increase in the likelihood of higher storms.

Speed ​​of movement and ability to stop

Storm speed can be an important factor in rainfall totals at a given location: A slower storm, such as Hurricane Harvey in 2017, provides a longer period of time for rain to accumulate.

There is evidence of a global slowdown in hurricane speed, but the quality of historical data limits understanding at this point, and the potential mechanisms are not yet understood.

The frequency of storms in the future is less clear

How the number of hurricanes that form each year might change is another important question that is not well understood.

There is no definitive theory that explains the number of storms in the current climate or how it will change in the future.

In addition to the right environmental conditions to fuel a storm, the storm must form from a disturbance in the atmosphere. There is currently a debate in the scientific community about the role of these pre-storm disturbances in determining the number of storms in the current and future climate.

Natural climate fluctuations, such as El Niño and La Niña, also have a significant impact on whether and where hurricanes develop. How these and other natural variations will change in the future and affect future hurricane activity is a matter of active research.

How has climate change affected Ian?

Scientists are conducting performance studies on individual storms to gauge how likely global warming has affected them, and those studies are ongoing for Ian.

However, individual performance studies are not needed to be sure that the storm occurred in an environment that human-induced climate change made more favorable for a stronger, wetter, and higher-intensity disaster. Human activities will continue to increase the chance of even worse storms year after year unless rapid and dramatic reductions in greenhouse gas emissions are made.

This article was originally published on The conversation with Mathew Barlow at UMass Lowell and Suzana J. Camargo at Columbia University. Read the original article here.

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