Observed increases in North Atlantic tropical cyclone peak intensification rates

This new paper in Nature Scientific Reports claims to identify a trend in hurricane intensification so significant that it’s utterly absurd that hurricane forecasters and modelers wouldn’t have noticed and identified it previously. This triggers an intense bright red bullshit detector.

As others to dig into this study we’ll likely see the flawed reasoning that was applied to tease out its conclusion. It’s outside my wheelhouse to do so. When the smoke clears it will be just one more example of how Nature mag has flushed what little credibility it had down the toilet.

[Update since I scheduled this article. Ryan Maue has weighed in on X (formerly Twitter).]

Here is the Abstract and Introduction.

Abstract

Quickly intensifying tropical cyclones (TCs) are exceptionally hazardous for Atlantic coastlines. An analysis of observed maximum changes in wind speed for Atlantic TCs from 1971 to 2020 indicates that TC intensification rates have already changed as anthropogenic greenhouse gas emissions have warmed the planet and oceans. Mean maximum TC intensification rates are up to 28.7% greater in a modern era (2001–2020) compared to a historical era (1971–1990). In the modern era, it is about as likely for TCs to intensify by at least 50 kts in 24 h, and more likely for TCs to intensify by at least 20 kts within 24 h than it was for TCs to intensify by these amounts in 36 h in the historical era. Finally, the number of TCs that intensify from a Category 1 hurricane (or weaker) into a major hurricane within 36 h has more than doubled in the modern era relative to the historical era. Significance tests suggest that it would have been statistically impossible to observe the number of TCs that intensified in this way during the modern era if rates of intensification had not changed from the historical era.

Introduction

Tropical cyclones (TCs) are the most damaging natural hazard to regularly impact the U.S. Atlantic and Gulf coasts^1,2,3,4. From 2012 to 2022, over 160 “billion-dollar” weather and climate disasters impacted the U.S; 24 of these events were TCs, including the six costliest disasters on record during this time⁵. Many of the most damaging TCs to impact the U.S. in recent years have been notable for the speed at which they have intensified. For instance, Hurricane Maria (2017), the climate disaster with the highest death toll since 1980, and the 4th highest economic cost in the last four decades, strengthened from a tropical storm to a Category 5 hurricane on the Saffir-Simpson scale in just over 48 hours^5,6,7. Hurricanes Harvey (2017), Ian (2022), Sandy (2012), Ida (2021), and Irma (2017), the five other costliest U.S. weather and climate disasters in the last decade, all similarly strengthened rapidly, with most evolving from tropical storms to major hurricanes (Category 3 on the Saffir-Simpson scale or greater) in under three days^{5,8,9,10,11,12}.

The fastest TC intensification rates often occur in areas of unusually warm upper ocean and sea surface temperatures (SSTs)^13,14,15,16. These warm waters serve as a critical energy source for the strengthening storms which act as heat engines, transporting excess warmth from the oceans and atmosphere in the tropics to higher latitudes¹⁷. As anthropogenic emissions have warmed the planet, the world’s oceans have warmed at the surface, where average temperatures have increased ~ 0.88 °C from 1850–1900 to 2011–2020¹⁸. The rate at which ocean surfaces have warmed has also accelerated, with 0.60 °C of this warming occurring since 1980¹⁸. Considering the role of warm upper ocean water and SSTs in the fastest TC intensification rates^13,14,15,16, it is reasonable to expect that we may observe an increase in TC intensification rates that coincides with warming ocean temperatures in recent decades^{19,20,21,22,23,24}. Given the highly-damaging nature of many TCs that intensify rapidly, and the operational and forecasting challenges posed by TCs that intensify most quickly^25,26, there is an urgent need to better understand how intensification rates of TCs may already have changed in a warming climate.

Various past studies have sought to understand how rapid intensification of TCs may evolve in a warmer climate, including work focused on understanding how intensification events that occur within certain regions or fall above a certain threshold may change over time^{22,27,28,29,30,31,32,33,34}. For example, Ref.³³ examined intensification trends in landfalling TCs in East and Southeast Asia, and found that a 12–15% increase in the intensity of such storms at landfall was primarily due to an increase in the rate at which they intensified. In the Atlantic basin, multiple studies have sought to understand how TC intensification rates have changed near major coastlines. For instance, Ref.²² found that there was an increased likelihood for TCs to intensify quickly near the U.S. coast during times when basin-wide conditions were generally less favorable for such intensification events. Also focusing on intensification near U.S. coastlines, Ref.²⁸ found that although the mean 24-h intensification rate of TCs increased by 1.2 kts/6 h near the U.S. Atlantic coast from 1979 to 2018, no similar increase was observed along the U.S. Gulf coast. Using a similar focus region, Ref.³² found that, when considering U.S. landfalling TCs, there was a tendency for TCs that intensified rapidly in the 24 h prior to landfall to decay more slowly after landfall.

Elsewhere in the Atlantic, Ref.²⁷ notes that in the central and eastern tropical Atlantic, the 95th percentile of 24-h TC intensity changes increased at 3.8 kts per decade from 1986 to 2015. Using the same threshold of the 95th percentile of 24-h intensity changes to define rapid intensification, Ref.³⁰ suggest that it is possible to detect an anthropogenic-related increase in Atlantic TC rapid intensification rates. Adopting a slightly different threshold of 30 kts/24 h to define rapid intensification, Ref.²⁹ identify no trend in TC rapid intensification tied to warming from 1950 to 2014, but do note key spatial and temporal patterns in rapid intensification events in the Atlantic.

This study adds to the considerable previous research efforts described above by developing a broader assessment of overall basin-wide changes in the magnitude of peak Atlantic TC intensification rates. This work focuses on the Atlantic basin as a whole, rather than a subset of storms that occur in a specific portion of the basin. Furthermore, no arbitrary thresholds of intensification are used in this study to classify a TC rapid intensification event—instead, the work fills a key knowledge gap by assessing overall changes to the peak intensification rates achieved by all TCs across 12-, 24- and 36-h windows during the 5 decades spanning from 1971 to 2020. Results indicate broad increases to observed TC intensification rates over the past 50 years. These findings illustrate a vital need to not only work towards climate mitigation to limit future warming and thus additional changes in TC intensification rates, but also for emergency preparedness plans and resilience measures that will allow our coastlines to adapt to TCs that have already begun to exhibit increased rates of strengthening.

Source: https://www.nature.com/articles/s41598-023-42669-y