What role did climate play in a two-week series of hurricanes?

Published 03.10.2022 23:54 by

Mathew Barlow and Suzana J Camargo

When Hurricane Ian struck Florida, it was one of the most powerful United States hurricanes on record, and it followed a two-week series of massive, devastating storms around the world.

A few days earlier, Typhoon Noru in the Philippines gave new meaning to rapid intensification when it exploded from a tropical storm with winds of 80 km/h to a Category 5 monster with winds of 155 km/h the next day. Hurricane Fiona devastated Puerto Rico and then became Canada’s strongest storm on record. Typhoon Merbok gained strength over a warm Pacific Ocean, tearing through more than 1,000 miles of Alaska’s coastline.

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

Many people ask about the role rising global temperatures play in storms like these. It’s not always an easy answer.

Record-breaking hurricanes in late September 2022. Mathew Barlow

It is clear that climate change is raising the ceiling for hurricane strength and rain rate, and that it is also raising average sea levels and hence storm surge. The impact on the total number of hurricanes is currently uncertain, as are other aspects. But when hurricanes do occur, we expect more of them to be large storms. Hurricane Ian and other recent storms, including the 2020 Atlantic season, provide a picture of what that can look like.

For years, our research has focused on hurricanes, climate change and the hydrological cycle. Here’s what scientists know so far.

Precipitation: The temperature has a clear influence

The temperature of the ocean and the atmosphere are crucial for the development of hurricanes.

Hurricanes are fueled by the release of heat as water evaporating from the sea surface condenses in the storm’s rain.

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

Simplified cross-section of a hurricane. Matthew Barlow

These are fundamental physical properties of the climate system, and this simplicity lends much confidence to scientists’ expectations for storm conditions as the planet warms. The potential for greater evaporation and higher rain rates generally applies to any type of land or sea storm.

This basic physical understanding, corroborated by computer simulations of these storms in current and future climates and recent events, leads to high confidence that hurricane precipitation rates are increasing by at least seven percent for every degree of warming.

Storm strength and rapid intensification

Scientists are also very confident that wind speeds will increase in a warming climate and that the proportion of storms strengthening into powerful Category 4 or 5 storms will increase. Similar to precipitation rates, intensity increases are based on the physics of extreme precipitation events.

Damage is exponentially related to wind speed, so stronger storms can have greater impacts on life and the economy. The damage potential of a Category 4 storm with winds of 150 mph, like Ian landing, is about 256 times greater than a Category 1 storm with winds of 47 mph.

Whether warming will cause storms to intensify faster is an active area of ​​research, with some models providing 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. Observations of Atlantic hurricanes date back to the 19th century, but they have only been considered reliable worldwide since the 1980s due to satellite coverage.

However, there is already some evidence that rapid intensification is increasing in the Atlantic.

Within the last two weeks of September 2022, both Noru and Ian showed rapid intensification. In the case of Ian, successful predictions of rapid intensification were made several days in advance when the storm was still a tropical depression. They illustrate the significant advances in intensity forecasts over the past few years, although improvements have not been uniform.

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

Storm surge: Two important influences

Storm surge – the rise in water on a coast caused by a storm – depends on a number of factors including storm speed, storm strength, wind direction and the topography of the seabed on the coast. Climate change could have at least two important influences.

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

Speed ​​of movement and potential to stall

The speed of the storm can be an important factor in the total precipitation amount at a given location: A slower storm, like Hurricane Harvey in 2017, offers a longer time in which rain can accumulate.

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

The frequency of storms in the future is less clear

How the number of hurricanes that form each year can 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.

Aside from having the right environmental conditions in place to fuel a storm, the storm must form from a disturbance in the atmosphere. The scientific community is currently debating the role of these fore-storm disturbances in determining the number of storms in the current and future climate.

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

How much has climate change affected Ian?

Scientists are conducting attribution studies on individual storms to estimate how much global warming is likely to have affected them, and these studies are currently being conducted for Ian.

However, no individual attribution studies are needed to be certain that the storm occurred in an environment made more conducive to a stronger, rainier, stronger disaster due to human-caused climate change. Human activity will increase the chances of even worse storms year after year unless rapid and dramatic reductions in greenhouse gas emissions are made.

Mathew Barlow is Professor of Climate Science at UMass Lowell.

Suzana J. Camargo is the Lamont Research Professor of Ocean and Climate Physics at Columbia University.

This article appears courtesy of The Conversation and can be found in its original form here.

The opinions expressed herein are those of the author and not necessarily those of The Maritime Executive.